MnO2 Motor: A Prospective Cancer-Starving Therapy Promoter.

PubMed

Zhang, Yao-Hui; Qiu, Wen-Xiu; Zhang, Mingkang; Zhang, Lu; Zhang, Xian-Zheng

2018-05-02

Here, a tumor-targeted MnO 2 motor nanosystem (designed as MG/HA) was constructed by the assembly of glucose oxidase (GOD), manganese dioxide (MnO 2 ), and glycoprotein CD44-targeting polymer hyaluronic acid (HA) to elevate cancer-starving therapy efficacy in solid tumor. Upon the specific uptake of MG/HA by CD44 overexpressed cancer cells, GOD catalyzed the oxidation of glucose into gluconic acid and hydrogen peroxide (H 2 O 2 ) accompanying the consumption of oxygen (O 2 ). Meanwhile, MnO 2 would react with H 2 O 2 and acid to generate O 2 , which is in turn supplied to the glucose-depletion process, running like a loop. As a result, MnO 2 is displayed as a motor to promote the rate of glucose depletion that contributed to the starving therapy. In contrast to G/HA, MG/HA could not only achieve effective glucose consumption to depress cancer progression, but also alleviate hypoxia and reduce the expression of Glut1 to inhibit the metabolism for further restraining the tumor aggressiveness and metastasis. The concept of MnO 2 motor shows a promising prospect to overcome the restriction of the starving therapy.

MnO2/carbon nanowalls composite electrode for supercapacitor application

NASA Astrophysics Data System (ADS)

Hassan, Sameh; Suzuki, Masaaki; Mori, Shinsuke; El-Moneim, Ahmed Abd

2014-03-01

Amorphous MnO2/carbon nanowalls composite films are developed for the supercapacitor applications. Synthesis of carbon nanowalls template is performed by plasma-enhanced chemical vapor deposition in a CO/H2 microwave discharge system. A well dispersion of amorphous MnO2 domains throughout carbon nanowalls template is obtained by potentiostatic anodic deposition technique. Carbon nanowalls enable to improve the capacitive behavior and rate capability of MnO2, a specific capacitance of 851 F g-1 at a current density of 1 mA cm-2 and charge transfer resistance of 1.02 Ω are obtained. MnO2/carbon nanowalls composite film exhibits energy density of 118 wh kg-1, power density of 783 wh kg-1, and capacitance retention of 92% after long cycle life of 2000 cycles by charging and discharging at 3 mA cm-2. The high density of atomic scale graphitic edges and large surface area of carbon nanowalls in conjunction with the presence of amorphous MnO2 domains facilitate rapid electron and ion transport and hence offering the potential of the improved capacitive behavior.

Enhanced specific capacitance of an electrophoretic deposited MnO2-carbon nanotube supercapacitor

NASA Astrophysics Data System (ADS)

Tagsin, Patin; Klangtakai, Pawinee; Harnchana, Viyada; Amornkitbamrung, Vittaya; Pimanpang, Samuk; Kumnorkaew, Pisist

2017-12-01

MnO2 and MnO2-carbon nanotubes (CNT) composite films were grown directly on stainless- steel substrates using an electrophoretic process employing supercapacitor electrodes. An electrophoretic MnO2 film with a nanoplate-like structure was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Supercapacitor performance was studied using cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS). The specific capacitance (SC) of the electrophoretic MnO2 film was 60 F/g at 1 A/g, with a 38.33% retention of the initial SC values after 1000 cycles. The low SC value of the MnO2 films was attributed to the high series and charge-transfer resistances of 1.70 Ω and 3.20, respectively. The MnO2-CNT composites with the addition of 0.04, 0.06 and 0.08 g CNT to the electrophoretic MnO2 film were found to greatly increase the SC to 300, 206 and 169 F/g at 1 A/g, respectively. The series and charge-transferred resistances of MnO2-CNT composite films decreased to 1.38 - 1.52 Ω and 2.62 - 2.86 Ω, respectively. The SC improvement of the composite electrodes was attributed to presence of two active storage materials (MnO2 and CNT), a high film specific surface area and electrical conductivity.

Oxidation-etching preparation of MnO2 tubular nanostructures for high-performance supercapacitors.

PubMed

Zhu, Jixin; Shi, Wenhui; Xiao, Ni; Rui, Xianhong; Tan, Huiteng; Lu, Xuehong; Hng, Huey Hoon; Ma, Jan; Yan, Qingyu

2012-05-01

1D hierarchical tubular MnO(2) nanostructures have been prepared through a facile hydrothermal method using carbon nanofibres (CNFs) as sacrificial template. The morphology of MnO(2) nanostructures can be adjusted by changing the reaction time or annealing process. Polycrystalline MnO(2) nanotubes are formed with a short reaction time (e.g., 10 min) while hierarchical tubular MnO(2) nanostructures composed of assembled nanosheets are obtained at longer reaction times (>45 min). The polycrystalline MnO(2) nanotubes can be further converted to porous nanobelts and sponge-like nanowires by annealing in air. Among all the types of MnO(2) nanostructures prepared, tubular MnO(2) nanostructures composed of assembled nanosheets show optimized charge storage performance when tested as supercapacitor electrodes, for example, delivering an power density of 13.33 kW·kg(-1) and a energy density of 21.1 Wh·kg(-1) with a long cycling life over 3000 cycles, which is mainly related to their features of large specific surface area and optimized charge transfer pathway.

Enhanced Cycleability of Amorphous MnO2 by Covering on α-MnO2 Needles in an Electrochemical Capacitor

PubMed Central

Liu, Quanbing; Yang, Juan; Wang, Hui; Pollet, Bruno G.; Wang, Rongfang

2017-01-01

An allomorph MnO2@MnO2 core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N2 adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO2 nano-sheets which were well grown onto the surface of α-MnO2 nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaic pseudo-capacity of the MnO2@MnO2 capacitor electrode contributed to a specific capacitance of 150.3 F·g−1 at a current density of 0.1 A·g−1. Long cycle life experiments on the as-prepared MnO2@MnO2 sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g−1. This retention value was found to be significantly higher than those reported for amorphous MnO2-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO2@MnO2 was due to the supporting role of α-MnO2 nano-needle core and the outer amorphous MnO2 layer. PMID:28837099

Spatially-controlled NiCo2O4@MnO2 core–shell nanoarray with hollow NiCo2O4 cores and MnO2 flake shells: an efficient catalyst for oxygen evolution reaction

NASA Astrophysics Data System (ADS)

Xue, Hairong; Yu, Hongjie; Li, Yinghao; Deng, Kai; Xu, You; Li, Xiaonian; Wang, Hongjing; Wang, Liang

2018-07-01

Control of structures and components of the nanoarray catalysts is very important for electrochemical energy conversion. Herein, unique NiCo2O4@MnO2 core–shell nanoarray with hollow NiCo2O4 Cores and MnO2 flake shells is in situ fabricated on carbon textile via a two-step hydrothermal treatment followed by a subsequent annealing. The as-made nanoarray is highly active and durable catalyst for oxygen evolution reaction in alkaline media attribute to the synergetic effect derived from spatially separated nanoarray with favorable NiCo2O4 and MnO2 compositions.

Spatially-controlled NiCo2O4@MnO2 core-shell nanoarray with hollow NiCo2O4 cores and MnO2 flake shells: an efficient catalyst for oxygen evolution reaction.

PubMed

Xue, Hairong; Yu, Hongjie; Li, Yinghao; Deng, Kai; Xu, You; Li, Xiaonian; Wang, Hongjing; Wang, Liang

2018-07-13

Control of structures and components of the nanoarray catalysts is very important for electrochemical energy conversion. Herein, unique NiCo 2 O 4 @MnO 2 core-shell nanoarray with hollow NiCo 2 O 4 Cores and MnO 2 flake shells is in situ fabricated on carbon textile via a two-step hydrothermal treatment followed by a subsequent annealing. The as-made nanoarray is highly active and durable catalyst for oxygen evolution reaction in alkaline media attribute to the synergetic effect derived from spatially separated nanoarray with favorable NiCo 2 O 4 and MnO 2 compositions.

Porous MnO2 prepared by sol-gel method for electrochemical supercapacitor

NASA Astrophysics Data System (ADS)

Bazzi, K.; Kumar, A.; Jayakumar, O. D.; Nazri, G. A.; Naik, V. M.; Naik, R.

2015-03-01

MnO2 has attracted great attention as material for electrochemical pseudocapacitor due to its high theoretical specific faradic capacitance (~ 1370 F .g-1) , environmental friendliness and wide potential window in both aqueous and nonaqueous electrolytes. However, the MnO2 has a low surface area which depresses its electrochemical performance. The amorphous α-MnO2 composite was synthesized by sol gel method in the presence of the tri-block copolymer P123. Our aim is to investigate the role of P123 on the electrochemical performance of MnO2. The samples with and without P123 were prepared and characterized by x-ray diffraction (XRD), SEM, TEM and Brunauer-Emmett-Teller (BET) method. The electrochemical performances of the amorphous MnO2 composites as the electrode materials for supercapacitors were evaluated by cyclic voltammetry and AC impedance measurements in a 1M Na2SO4 solution. The results show that the sample prepared without P123 exhibited a relatively low specific capacitance of 28F .g-1, whereas the porous MnO2 prepared with P123 exhibited 117 F .g-1at 5 mV/s. The results of crystalline MnO2 composites will also be presented. The authors acknowledge the support from the Richard J. Barber Foundation for Interdisciplinary Research.

Hierarchical MnO2/SnO2 heterostructures for a novel free-standing ternary thermite membrane.

PubMed

Yang, Yong; Zhang, Zhi-Cheng; Wang, Peng-Peng; Zhang, Jing-Chao; Nosheen, Farhat; Zhuang, Jing; Wang, Xun

2013-08-19

We report the synthesis of a novel hierarchical MnO2/SnO2 heterostructures via a hydrothermal method. Secondary SnO2 nanostructure grows epitaxially on the surface of MnO2 backbones without any surfactant, which relies on the minimization of surface energy and interfacial lattice mismatch. Detailed investigations reveal that the cover density and morphology of the SnO2 nanostructure can be tailored by changing the experimental parameter. Moreover, we demonstrate a bottom-up method to produce energetic nanocomposites by assembling nanoaluminum (n-Al) and MnO2/SnO2 hierarchical nanostructures into a free-standing MnO2/SnO2/n-Al ternary thermite membrane. This assembled approach can significantly reduce diffusion distances and increase their intimacy between the components. Different thermite mixtures were investigated to evaluate the corresponding activation energies using DSC techniques. The energy performance of the ternary thermite membrane can be manipulated through different components of the MnO2/SnO2 heterostructures. Overall, our work may open a new route for new energetic materials.

Sonochemical assisted synthesis MnO2/RGO nanohybrid as effective electrode material for supercapacitor.

PubMed

Ghasemi, Shahram; Hosseini, Sayed Reza; Boore-Talari, Omid

2018-01-01

Manganese dioxide (MnO 2 ) needle-like nanostructures are successfully synthesized by a sonochemical method from an aqueous solution of potassium bromate and manganese sulfate. Also, hybride of MnO 2 nanoparticles wrapped with graphene oxide (GO) nanosheets are fabricated through an electrostatic coprecipitation procedure. With adjusting pH at 3.5, positive and negative charges are created on MnO 2 and on GO, respectively which can electrostatically attract to each other and coprecipitate. Then, MnO 2 /GO pasted on stainless steel mesh is electrochemically reduced by applying -1.1V to obtain MnO 2 /RGO nanohybrid. The structure and morphology of the MnO 2 and MnO 2 /RGO nanohybrid are examined by Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDX), and thermal gravimetric analysis (TGA). The capacitive behaviors of MnO 2 and MnO 2 /RGO active materials on stainless steel meshes are investigated by cyclic voltammetry (CV), galvanostatic charge/discharge test and electrochemical impedance spectroscopy (EIS) by a three-electrode experimental setup in an aqueous solution of 0.5M sodium sulfate in the potential window of 0.0-1.0V. The electrochemical investigations reveal that MnO 2 /RGO exhibits high specific capacitance (C s ) of 375Fg -1 at current density of 1Ag -1 and good cycle stability (93% capacitance retention after 500 cycles at a scan rate of 200mVs -1 ). The obtained results give good prospect about the application of electrostatic coprecipitation method to prepare graphene/metal oxides nanohybrids as effective electrode materials for supercapacitors. Copyright © 2017 Elsevier B.V. All rights reserved.

Wire-type MnO2/Multilayer graphene/Ni electrode for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Hu, Minglei; Liu, Yuhao; Zhang, Min; Wei, Helin; Gao, Yihua

2016-12-01

Commercially available wearable energy storage devices need a wire-type electrode with high strength, conductivity and electrochemical performance, as well as stable structure under deformation. Herein, we report a novel wire-type electrode of hierarchically structure MnO2 on Ni wire with multilayer graphene (MGr) as a buffer layer to enhance the electrical conductivity of the MnO2 and interface contact between the MnO2 and Ni wire. Thus, the wire-type MnO2/MGr/Ni electrode has a stable and high quality interface. The wire-type supercapacitor (WSC) based on wire-type MnO2/MGr/Ni electrode exhibits good electrochemical performance, high rate capability, extraordinary flexibility, and superior cycle lifetime. Length (area, volumetric) specific capacitance of the WSC reaches 6.9 mF cm-1 (73.2 mF cm-2, 9.8 F cm-3). Maximum length (volumetric) energy density of the WSC based on MnO2/MGr/Ni reaches 0.62 μWh cm-1 (0.88 mWh cm-3). Furthermore, the WSC has a short time constant (0.5-400 ms) and exhibits minimal change in capacitance under different bending shapes.

Hierarchical MnO2 nanosheets synthesized via electrodeposition-hydrothermal method for supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Zheng, Dongdong; Qiang, Yujie; Xu, Shenying; Li, Wenpo; Yu, Shanshan; Zhang, Shengtao

2017-02-01

Metal oxides have emerged as one kind of important supercapacitor electrode materials. Herein, we report hierarchical MnO2 nanosheets prepared of indium tin oxide (ITO) coated glass substrates via a hybrid two-step protocol, including a cathodic electrodeposition technique and a hydrothermal process. The samples are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX), and transmission electron microscope (TEM). SEM and TEM images show that the as-synthesized MnO2 nanosheets are hierarchical and porous, which could increase the active surface and short paths for fast ion diffusion. The results of nitrogen adsorption-desorption analysis indicate that the BET surface area of the MnO2 nanosheets is 53.031 m2 g-1. Furthermore, the electrochemical properties of the MnO2 are elucidated by cyclic voltammograms (CV), galvanostatic charge-discharge (GCD) tests, and electrochemical impedance spectroscopy (EIS) in 0.1 M Na2SO4 electrolyte. The electrochemical results demonstrate that the as-grown MnO2 nanosheet exhibits an excellent specific capacitance of 335 F g-1 at 0.5 A g-1 when it is applied as a potential electrode material for an electrochemical supercapacitor. Additionally, the MnO2 nanosheet electrode also presents high rate capability and good cycling stability with 91.8% retention after 1000 cycles. These excellent properties indicate that the hierarchical MnO2 nanosheets are a potential electrode material for electrochemical supercapacitors.

Self-assembled spongy-like MnO2 electrode materials for supercapacitors

NASA Astrophysics Data System (ADS)

Dong, Meng; Zhang, Yu Xin; Song, Hong Fang; Qiu, Xin; Hao, Xiao Dong; Liu, Chuan Pu; Yuan, Yuan; Li, Xin Lu; Huang, Jia Mu

2012-08-01

Mesoporous spongy-like MnO2 has been synthesized via a facile and biphasic wet method, accompanied with tetraoctylammonium bromide (TOAB) as a soft template under ambient condition. A well-defined spongy morphology of MnO2 with uniform filament diameters 10-20 nm have been observed by FESEM, TEM, HRTEM, XRD, FT-IR,TGA-DSC studies. Further physical characterizations revealed that MnO2 sponges owned a large surface area of 155 m2 g-1 with typical mesoporous appearance. A specific capacitance value as high as 336 F g-1 was obtained. This improved capacitive behavior was attributed to the large surface area, morphology nature of nano-MnO2, and its broad pore size distribution.

Binder free MnO2/PIn electrode material for supercapacitor application

NASA Astrophysics Data System (ADS)

Purty, B.; Choudhary, R. B.; Kandulna, R.; Singh, R.

2018-05-01

Electrochemically stable MnO2/PIn nanocomposite was synthesized via in-situ chemical oxidative polymerization process. The structural and morphological properties were studied through FTIR and FESEM characterizing techniques. Sphere like PIn and MnO2 nanorods offers interacting surface for charge transfer action. The electrochemical properties were investigated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopic (EIS) techniques. The significant enhancement in capacitance value with 95% coulombic efficiency and relatively low equivalent series resistance (ESR)˜0.4 Ω proved that MnO2/PIn nanocomposite is an excellent performer as an electrode material in the spectrum of supercapcitors and optoelectronic devices.

3D MnO2-graphene composites with large areal capacitance for high-performance asymmetric supercapacitors

NASA Astrophysics Data System (ADS)

Zhai, Teng; Wang, Fuxin; Yu, Minghao; Xie, Shilei; Liang, Chaolun; Li, Cheng; Xiao, Fangming; Tang, Renheng; Wu, Qixiu; Lu, Xihong; Tong, Yexiang

2013-07-01

In this paper, we reported an effective and simple strategy to prepare large areal mass loading of MnO2 on porous graphene gel/Ni foam (denoted as MnO2/G-gel/NF) for supercapacitors (SCs). The MnO2/G-gel/NF (MnO2 mass: 13.6 mg cm-2) delivered a large areal capacitance of 3.18 F cm-2 (234.2 F g-1) and good rate capability. The prominent electrochemical properties of MnO2/G-gel/NF are attributed to the enhanced conductivities and improved accessible area for ions in electrolytes. Moreover, an asymmetric supercapacitor (ASC) based on MnO2/G-gel/NF (MnO2 mass: 6.1 mg cm-2) as the positive electrode and G-gel/NF as the negative electrode achieved a remarkable energy density of 0.72 mW h cm-3. Additionally, the fabricated ASC device also exhibited excellent cycling stability, with less than 1.5% decay after 10 000 cycles. The ability to effectively develop SC electrodes with high mass loading should open up new opportunities for SCs with high areal capacitance and high energy density.In this paper, we reported an effective and simple strategy to prepare large areal mass loading of MnO2 on porous graphene gel/Ni foam (denoted as MnO2/G-gel/NF) for supercapacitors (SCs). The MnO2/G-gel/NF (MnO2 mass: 13.6 mg cm-2) delivered a large areal capacitance of 3.18 F cm-2 (234.2 F g-1) and good rate capability. The prominent electrochemical properties of MnO2/G-gel/NF are attributed to the enhanced conductivities and improved accessible area for ions in electrolytes. Moreover, an asymmetric supercapacitor (ASC) based on MnO2/G-gel/NF (MnO2 mass: 6.1 mg cm-2) as the positive electrode and G-gel/NF as the negative electrode achieved a remarkable energy density of 0.72 mW h cm-3. Additionally, the fabricated ASC device also exhibited excellent cycling stability, with less than 1.5% decay after 10 000 cycles. The ability to effectively develop SC electrodes with high mass loading should open up new opportunities for SCs with high areal capacitance and high energy density. Electronic

Facile preparation of MnO2 nanorods and evaluation of their supercapacitive characteristics

NASA Astrophysics Data System (ADS)

Aghazadeh, Mustafa; Asadi, Maryam; Maragheh, Mohammad Ghannadi; Ganjali, Mohammad Reza; Norouzi, Parviz; Faridbod, Farnoush

2016-02-01

The first time pulsed base (OH-) electrogeneration to the cathodic electrodeposition of MnO2 in nitrate bath was applied and MnO2 nanorods were obtained. The deposition experiments were performed under a pulse current mode with typical on-times and off-times (ton = 10 ms and toff = 50 ms) and a peak current density of 2 mA cm-2 (Ia = 2 mA cm-2). The structural characterization with XRD and FTIR revealed that the prepared MnO2 is composed of both α and γ phases. Morphological evaluations through SEM and TEM revealed that the prepared MnO2 contains nanorods of relative uniform structures (with an average diameter of 50 nm). The electrochemical measurements through cyclic voltammetry and charge-discharge techniques revealed that the prepared MnO2 nanostructures reveal an excellent capacitive behavior with specific capacitance values of 242, 167 and 98 F g-1 under the applied current densities of 2, 5 and 10 A g-1, respectively. Also, excellent long-term cycling stabilities of 94.8%, 89.1%, and 76.5% were observed after 1000 charge-discharge cycles at the current densities of 2, 5 and 10 A g-1.

Controllable synthesis of MnO2/polyaniline nanocomposite and its electrochemical capacitive property

NASA Astrophysics Data System (ADS)

Meng, Fanhui; Yan, Xiuling; Zhu, Ye; Si, Pengchao

2013-04-01

Polyaniline (PANI) and MnO2/PANI composites are simply fabricated by one-step interfacial polymerization. The morphologies and components of MnO2/PANI composites are modulated by changing the pH of the solution. Formation procedure and capacitive property of the products are investigated by XRD, FTIR, TEM, and electrochemical techniques. We demonstrate that MnO2 as an intermedia material plays a key role in the formation of sample structures. The MnO2/PANI composites exhibit good cycling stability as well as a high capacitance close to 207 F g-1. Samples fabricated with the facile one-step method are also expected to be adopted in other field such as catalysis, lithium ion battery, and biosensor.

Controllable synthesis of MnO2/polyaniline nanocomposite and its electrochemical capacitive property

PubMed Central

2013-01-01

Polyaniline (PANI) and MnO2/PANI composites are simply fabricated by one-step interfacial polymerization. The morphologies and components of MnO2/PANI composites are modulated by changing the pH of the solution. Formation procedure and capacitive property of the products are investigated by XRD, FTIR, TEM, and electrochemical techniques. We demonstrate that MnO2 as an intermedia material plays a key role in the formation of sample structures. The MnO2/PANI composites exhibit good cycling stability as well as a high capacitance close to 207 F g−1. Samples fabricated with the facile one-step method are also expected to be adopted in other field such as catalysis, lithium ion battery, and biosensor. PMID:23594724

Synthesis and characterization of different MnO2 morphologies for lithium-air batteries

NASA Astrophysics Data System (ADS)

Choi, Hyun-A.; Jang, Hyuk; Hwang, Hyein; Choi, Mincheol; Lim, Dongwook; Shim, Sang Eun; Baeck, Sung-Hyeon

2014-09-01

Manganese dioxide (MnO2) was synthesized in the forms of nanorods, nanoparticles, and mesoporous structures and the characteristics of these materials were investigated. Crystallinities were studied by x-ray diffraction and morphologies by scanning and transmission electron microscopy. Average pore sizes and specific surface areas were analyzed using the Barret-Joyner-Halenda and Brunauer-Emmett-Teller methods, respectively. Samples were also studied by cyclic voltammetry using 1M aqueous KOH solution saturated with either O2 or N2 as electrolytes to investigate their ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) activities. Of the samples produced, mesoporous MnO2 exhibited the highest ORR and OER catalytic activities. Mesoporous MnO2 supported on a gas diffusion layer was also used as a catalyst on the air electrode (cathode) of a lithium-air battery in organic electrolyte. The charge-discharge behavior of mesoporous MnO2 was investigated at a current density 0.2 mAcm-2 in a pure oxygen environment. Mesoporous MnO2 electrodes showed stable cycleability up to 65 cycles at a cell capacity of 700 mAhg-1.

Morphology controlled MnO2 electrodeposited on carbon fiber paper for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Ye, Zhiguo; Li, Tao; Ma, Guang; Peng, Xinyuan; Zhao, Jun

2017-05-01

Four different morphologies of nanostructured MnO2 (nanospheres, nanosheets, nanoflowers and nanonods) were fabricated on a carbon fiber paper (CFP) substrate using a facile method of anodic electrodeposition by varying the H2SO4 concentration and current density. The fabricated composite electrodes were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and electrochemical techniques. The composite electrodes with MnO2 nanosphere/CFP, MnO2 nanosheet/CFP, MnO2 nanoflower/CFP and MnO2 nanonod/CFP achieved a relatively high specific capacitance (areal capacitance) of 134.4 F g-1 (0.20 F cm-2), 226.3 F g-1 (0.33 F cm-2), 235.6 F g-1 (0.35 F cm-2) and 362.5 F g-1 (0.54 F cm-2) at 0.5 A g-1, respectively. When the GV charging-discharging rate increased from 0.5 to 5 A g-1, the MnO2 nanorod/CFP composite decreased from 362.5 F g-1 (0.54 F cm-2) to 160.0 F g-1 (0.24 F cm-2), which is a relatively high retention of the original capacitance (i.e., 44.1%). All the composite electrodes with various nanostructured MnO2 morphologies under flat and bent states retained more than 95% and 90% of the initial capacitance after 5000 cycles at 5 A g-1, respectively, which demonstrates outstanding cycling stability. This study provides a novel approach for high-performance, morphology-controllable metal oxide electrodes for supercapacitors.

Synthesis and property of novel MnO2@polypyrrole coaxial nanotubes as electrode material for supercapacitors

NASA Astrophysics Data System (ADS)

Yao, Wei; Zhou, Hui; Lu, Yun

2013-11-01

Novel MnO2@polypyrrole (PPy) coaxial nanotubes have been prepared via a simple and green approach without any surfactant and additional oxidant. Under the acidic condition, MnO2 nanotubes act as both template and oxidant to initiate the polymerization of pyrrole monomers on its fresh-activated surface. Fourier transform infrared spectra (FT-IR), X-ray diffraction patterns (XRD), thermo-gravimetric analysis data (TG) and X-ray photoelectron spectra (XPS) suggest the formation of composite structure of MnO2@PPy. Also, FESEM and TEM images intuitively confirm that the PPy shell is coated uniformly on the surface of MnO2 nanotubes. Adjusting the concentrations of sulfuric acid or adding oxidant can modulate the morphology of the products accordingly. Due to the synergic effect between MnO2 core and PPy shell, the MnO2@PPy coaxial nanotubes possess better rate capability, larger specific capacitance of 380 F g-1, doubling the specific capacitance of MnO2 nanotubes, and good capacitance retention of 90% for its initial capacitance after 1000 cycles.

Synthesis and characterization of reduced graphene oxide decorated with CeO2-doped MnO2 nanorods for supercapacitor applications.

PubMed

Ojha, Gunendra Prasad; Pant, Bishweshwar; Park, Soo-Jin; Park, Mira; Kim, Hak-Yong

2017-05-15

A novel and efficient CeO 2 -doped MnO 2 nanorods decorated reduced graphene oxide (CeO 2 -MnO 2 /RGO) nanocomposite was successfully synthesized via hydrothermal method. The growth of the CeO 2 doped MnO 2 nanorods over GO sheets and reduction of GO were simultaneously carried out under hydrothermal treatment. The morphology and structure of as-synthesized nanocomposite were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, which revealed the formation of CeO 2 -MnO 2 decorated RGO nanocomposites. The electrochemical performance of as-prepared CeO 2 -MnO 2 /RGO nanocomposites as an active electrode material for supercapacitor was evaluated by cyclic voltammetry, charge-discharge, and electrochemical impedance spectroscopy (EIS) methods in 2M alkaline medium. The obtained results revealed that as-synthesized CeO 2 -MnO 2 /RGO nanocomposite exhibited higher specific capacitance (648F/g) as compared to other formulations (MnO 2 /RGO nanocomposites: 315.13 F/g and MnO 2 nanorods: 228.5 F/g) at the scan rate of 5mV/s. After 1000 cycles, it retained ∼90.4%, exhibiting a good stability. The high surface area, enhanced electrical conductivity, and good stability possess by the nanocomposite make this material a promising candidate to be applied as a supercapacitor electrode. Copyright © 2017 Elsevier Inc. All rights reserved.

3D MnO2-graphene composites with large areal capacitance for high-performance asymmetric supercapacitors.

PubMed

Zhai, Teng; Wang, Fuxin; Yu, Minghao; Xie, Shilei; Liang, Chaolun; Li, Cheng; Xiao, Fangming; Tang, Renheng; Wu, Qixiu; Lu, Xihong; Tong, Yexiang

2013-08-07

In this paper, we reported an effective and simple strategy to prepare large areal mass loading of MnO2 on porous graphene gel/Ni foam (denoted as MnO2/G-gel/NF) for supercapacitors (SCs). The MnO2/G-gel/NF (MnO2 mass: 13.6 mg cm(-2)) delivered a large areal capacitance of 3.18 F cm(-2) (234.2 F g(-1)) and good rate capability. The prominent electrochemical properties of MnO2/G-gel/NF are attributed to the enhanced conductivities and improved accessible area for ions in electrolytes. Moreover, an asymmetric supercapacitor (ASC) based on MnO2/G-gel/NF (MnO2 mass: 6.1 mg cm(-2)) as the positive electrode and G-gel/NF as the negative electrode achieved a remarkable energy density of 0.72 mW h cm(-3). Additionally, the fabricated ASC device also exhibited excellent cycling stability, with less than 1.5% decay after 10,000 cycles. The ability to effectively develop SC electrodes with high mass loading should open up new opportunities for SCs with high areal capacitance and high energy density.

Research Progress in MnO2 -Carbon Based Supercapacitor Electrode Materials.

PubMed

Zhang, Qun-Zheng; Zhang, Dian; Miao, Zong-Cheng; Zhang, Xun-Li; Chou, Shu-Lei

2018-04-30

With the serious impact of fossil fuels on the environment and the rapid development of the global economy, the development of clean and usable energy storage devices has become one of the most important themes of sustainable development in the world today. Supercapacitors are a new type of green energy storage device, with high power density, long cycle life, wide temperature range, and both economic and environmental advantages. In many industries, they have enormous application prospects. Electrode materials are an important factor affecting the performance of supercapacitors. MnO 2 -based materials are widely investigated for supercapacitors because of their high theoretical capacitance, good chemical stability, low cost, and environmental friendliness. To achieve high specific capacitance and high rate capability, the current best solution is to use MnO 2 and carbon composite materials. Herein, MnO 2 -carbon composite as supercapacitor electrode materials is reviewed including the synthesis method and research status in recent years. Finally, the challenges and future development directions of an MnO 2 -carbon based supercapacitor are summarized. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dissimilatory perchlorate reduction linked to aerobic methane oxidation via chlorite dismutase

NASA Astrophysics Data System (ADS)

Oremland, R. S.; Baesman, S. M.; Miller, L. G.

2013-12-01

The presence of methane (CH4) in the atmosphere of Mars is controversial yet the evidence has aroused scientific interest, as CH4 could be a harbinger of extant or extinct microbial life. There are various oxidized compounds present on the surface of Mars that could serve as electron acceptors for the anaerobic oxidation of CH4, including perchlorate (ClO4-). We examined the role of perchlorate, chlorate (ClO3-) and chlorite (ClO2-) as oxidants linked to CH4 oxidation. Dissimilatory perchlorate reduction begins with reduction of ClO4- to ClO2- and ends with dismutation of chlorite to yield chloride (Cl-) and molecular oxygen (O2). We explored the potential for aerobic CH4 oxidizing bacteria to couple with oxygen derived from chlorite dismutation during dissimilatory perchlorate reduction. Methane (0.2 kPa) was completely removed within several days from the N2-flushed headspace above cell suspensions of methanotrophs (Methylobacter albus strain BG8) and perchlorate reducing bacteria (Dechloromonas agitata strain CKB) in the presence of 5 mM ClO2-. Similar rates of CH4 consumption were observed for these mixed cultures whether they were co-mingled or segregated under a common headspace, indicating that direct contact of cells was not required for methane consumption to occur. We also observed complete removal of 0.2 kPa CH4 in bottles containing dried soil (enriched in methanotrophs by CH4 additions over several weeks) and D. agitata CKB and in the presence of 10 mM ClO2-. This soil (seasonally exposed sediment) collected from the shoreline of a freshwater lake (Searsville Lake, CA) demonstrated endogenous CH4 uptake as well as perchlorate, chlorate and chlorite reduction/dismutation. However, these experiments required physical separation of soil from the aqueous bacterial culture to allow for the partitioning of O2 liberated from chlorite dismutation into the shared headspace. Although dissimilatory reduction of ClO4- and ClO3- could be inferred from the

MnO2 nanorods/SiO2 sphere coated on single-wall carbon nanotubes as supercapacitor electrode for high energy storage applications

NASA Astrophysics Data System (ADS)

Iro, Zaharaddeen S.; Subramani, C.; Kesavan, T.; Dash, S. S.; Sasidharan, M.; Sundramoorthy, Ashok K.

2017-12-01

A composite of MnO2/SiO2 sphere was coated on single-wall carbon nanotubes (MnO2/SiO2/SWCNT) using one-pot hydrothermal synthesis method. KMnO4 was used as an oxidizing agent for mild functionalization of single-wall carbon nanotubes (SWCNT), and also as a precursor of MnO2. A comparative study in the presence of SiO2 and SWCNT was carried out using bare MnO2 as a reference. After addition of SiO2, the composite obtained showed an increase in both the specific capacitance and cycle life which can be associated with spherical shape of SiO2 which offered reduction sites for MnO2. With the addition of SWCNT less than 5%, the composite further showed an increase in capacitance and cycle life, this is because of the good conductive nature, excellent mechanical property and chemical stability of SWCNT. The electrochemical behaviour was studied using cyclic voltammetry and galvanostatic charge/discharge method in 1 M Na2SO4 electrolyte. The specific capacitance of MnO2, MnO2/SiO2 and MnO2/SiO2/SWCNT composite is 73.6 F g-1, 108.7 F g-1 and 136 F g-1 at a current density of 1 A g-1, respectively. The MnO2/SiO2/SWCNT energy density was 68 Wh kg-1 with power density of 444.4 W kg-1. The MnO2/SiO2/SWCNT composite retained 88% of its specific capacitance after 500 cycles. We envisage that this hybrid material could be applied for preparation of supercapacitor electrode.

Electrical Characteristics of MnO2 Doped Bismuth Borate Glass Systems

NASA Astrophysics Data System (ADS)

Nissar, Umair; Ahmad, Javed; Rana, Anwar Manzoor; Bukhari, S. H.; Jamil, M. T.; Khan, J. Alam; Shakeel, R.; Nadeem, M. Y.

2018-02-01

Transparent glasses have a large number of applications in the industry of electronics as well as optical devices. xMnO2-(25- x) Bi2O3-75H3BO3 (0 ≤ x ≤ 1.5 mol.%) transparent glasses have been prepared via melt-quench technique and characterized using dc electrical measurements, and by analyzing x-ray diffraction and Fourier transform infrared (FTIR) spectra. These characteristics were examined to understand the role of modifier oxides, i.e., Bi2O3 and MnO2 in the B2O3 glass network. Adding MnO2 into a glass network causes structural changes, which are responsible for any variations in electrical characteristics of bismuth borate glasses. Manganese bismuth borate glasses (MBBG) show Ohmic conduction at low fields; however, glasses with higher manganese content seem to conduct through bulk limited Poole-Frenkel mechanism. FTIR spectroscopy analyses depict the presence of BO3 and BO4 groups along with B-O-B and Bi-O-Bi bonding vibrations. Glasses with higher MnO2 content also show Mn-O bond vibrations. The reduction of BO4 groups and increase of BO3 units lead to the formation of non-bridging oxygens (NBOs) which are responsible for the variations in the electrical properties of these glasses.

Nanostructured MnO2 as Electrode Materials for Energy Storage

PubMed Central

Mauger, Alain

2017-01-01

Manganese dioxides, inorganic materials which have been used in industry for more than a century, now find great renewal of interest for storage and conversion of energy applications. In this review article, we report the properties of MnO2 nanomaterials with different morphologies. Techniques used for the synthesis, structural, physical properties, and electrochemical performances of periodic and aperiodic frameworks are discussed. The effect of the morphology of nanosized MnO2 particles on their fundamental features is evidenced. Applications as electrodes in lithium batteries and supercapacitors are examined. PMID:29149066

Nucleation/Growth Mechanisms and Morphological Evolution of Porous MnO2 Coating Deposited on Graphite for Supercapacitor

PubMed Central

Huang, Wenxin; Xu, Yunhe

2017-01-01

The nucleation and growth mechanisms of porous MnO2 coating deposited on graphite in MnSO4 solution were investigated in detail by cyclic voltammetry, chronoamperometry and scanning electron microscopy. The electrochemical properties of honeycomb-like MnO2 were evaluated by cycle voltammetry and galvanostatic charge-discharge. Results indicated that MnO2 was synthesized by the following steps: Mn2+→Mn3++e−, Mn3++2H2O→MnOOH+3H+, and MnOOH→MnO2+H++e−. The deposition of MnO2 was divided into four stages. A short incubation period (approximately 1.5 s) was observed, prior to nucleation. The decreasing trend of the current slowed as time increased due to nucleation and MnO2 growth in the second stage. A huge number of nuclei were formed by instantaneous nucleation, and these nuclei grew and connected with one another at an exceedingly short time (0.5 s). In the third stage, the gaps in-between initial graphite flakes were filled with MnO2 until the morphology of the flakes gradually became similar to that of the MnO2-deposited layer. In the fourth stage, the graphite electrode was covered completely with a thick and dense layer of MnO2 deposits. All MnO2 electrodes at different deposition times obtained nearly the same specific capacitance of approximately 186 F/g, thus indicating that the specific capacitance of the electrodes is not related with deposition time. PMID:29048377

Functionalization of biomass carbonaceous aerogels: selective preparation of MnO2@CA composites for supercapacitors.

PubMed

Ren, Yumei; Xu, Qun; Zhang, Jianmin; Yang, Hongxia; Wang, Bo; Yang, Daoyuan; Hu, Junhua; Liu, Zhimin

2014-06-25

Functionalized porous carbon materials with hierarchical structure and developed porosity coming from natural and renewable biomass have been attracting tremendous attention recently. In this work, we present a facile and scalable method to synthesize MnO2 loaded carbonaceous aerogel (MnO2@CA) composites via the hydrothermal carbonaceous (HTC) process. We employ two reaction systems of the mixed metal ion precursors to study the optimal selective adsorption and further reaction of MnO2 precursor on CA. Our experimental results show that the system containing KMnO4 and Na2S2O3·5H2O exhibits better electrochemical properties compared with the reaction system of MnSO4·H2O and (NH4)2S2O8. For the former, the obtained MnO2@CA displays the specific capacitance of 123.5 F·g(-1). The enhanced supercapacitance of MnO2@CA nanocomposites could be ascribed to both electrochemical contributions of the loaded MnO2 nanoparticles and the porous structure of three-dimensional carbonaceous aerogels. This study not only indicates that it is vital for the reaction systems to match with porous carbonaceous materials, but also offers a new fabrication strategy to prepare lightweight and high-performance materials that can be used in energy storage devices.

Synthesis of honeycomb MnO2 nanospheres/carbon nanoparticles/graphene composites as electrode materials for supercapacitors

NASA Astrophysics Data System (ADS)

Xiong, Yachao; Zhou, Min; Chen, Hao; Feng, Lei; Wang, Zhao; Yan, Xinzhu; Guan, Shiyou

2015-12-01

Improving the electrochemical performance of manganese dioxide (MnO2) electrodes is of great significance for supercapacitors. In this study, a novel honeycomb MnO2 nanospheres/carbon nanoparticles/graphene composites has been fabricated through freeze-drying method. The honeycomb MnO2 nanospheres are well inserted and dispersed on the graphene. Carbon nanoparticles in the composites act as spacers to effectively prevent graphene from restacking and agglomeration, construct efficient 3D conducting architecture with graphene for honeycomb MnO2 nanospheres, and alleviate the aggregation of honeycomb MnO2 nanospheres by separating them from each other. As a result, such honeycomb MnO2 nanospheres/carbon nanoparticles/graphene composites display much improved electrochemical capacitive performance of 255 F g-1 at a current density of 0.5 A g-1, outstanding rate capability (150 F g-1 remained at a current density of 20 A g-1) and good cycling stability (83% of the initial capacitance retained after 1000 charge/discharge cycles). The strategy for the synthesis of these composites is very effective.

MnO2 Nanorods Intercalating Graphene Oxide/Polyaniline Ternary Composites for Robust High-Performance Supercapacitors

NASA Astrophysics Data System (ADS)

Han, Guangqiang; Liu, Yun; Zhang, Lingling; Kan, Erjun; Zhang, Shaopeng; Tang, Jian; Tang, Weihua

2014-04-01

New ternary composites of MnO2 nanorods, polyaniline (PANI) and graphene oxide (GO) have been prepared by a two-step process. The 100 nm-long MnO2 nanorods with a diameter ~20 nm are conformably coated with PANI layers and fastened between GO layers. The MnO2 nanorods incorporated ternary composites electrode exhibits significantly increased specific capacitance than PANI/GO binary composite in supercapacitors. The ternary composite with 70% MnO2 exhibits a highest specific capacitance reaching 512 F/g and outstanding cycling performance, with ~97% capacitance retained over 5000 cycles. The ternary composite approach offers an effective solution to enhance the device performance of metal-oxide based supercapacitors for long cycling applications.

FeOOH-loaded MnO2 nano-composite: An efficient emergency material for thallium pollution incident.

PubMed

Chen, Meiqing; Wu, Pingxiao; Yu, Langfeng; Liu, Shuai; Ruan, Bo; Hu, Haihui; Zhu, Nengwu; Lin, Zhang

2017-05-01

A FeOOH-loaded MnO 2 nano-composite was developed as an emergency material for Tl(I) pollution incident. Structural characterizations showed that FeOOH successfully loaded onto MnO 2 , the nanosheet-flower structure and high surface area (191 m 2  g -1 ) of material contributed to the excellent performance for Tl(I) removal. FeOOH-loaded MnO 2 with a Fe/Mn molar ratio of 1:2 exhibited a noticeable enhanced capacity for Tl(I) removal compared to that of pure MnO 2 . The outstanding performance for Tl(I) removal involves in extremely high efficiency (achieved equilibrium and drinking water standard within 4 min) and the large maximum adsorption capacity (450 mg g -1 ). Both the control-experiment and XPS characterization proved that the removal mechanism of Tl(I) on FeOOH-loaded MnO 2 included adsorption and oxidation: the oxidation of MnO 2 played an important role for Tl(I) removal, and the adsorption of FeOOH loaded on MnO 2 enhanced Tl(I) purification at the same time. In-depth purification of Tl(I) had reach drinking water standards (0.1 μg L -1 ) at pH above 7, and there wasn't security risk produced from the dissolution of Mn 2+ and Fe 2+ . Moreover, the as-prepared material could be utilized as a recyclable adsorbent regenerated by using NaOH-NaClO binary solution. Therefore, the synthesized FeOOH-loaded MnO 2 in this study has the potential to be applied as an emergency material for thallium pollution incident. Copyright © 2017 Elsevier Ltd. All rights reserved.

Materials and fabrication of electrode scaffolds for deposition of MnO2 and their true performance in supercapacitors

NASA Astrophysics Data System (ADS)

Cao, Jianyun; Li, Xiaohong; Wang, Yaming; Walsh, Frank C.; Ouyang, Jia-Hu; Jia, Dechang; Zhou, Yu

2015-10-01

MnO2 is a promising electrode material for high energy supercapacitors because of its large pseudo-capacitance. However, MnO2 suffers from low electronic conductivity and poor cation diffusivity, which results in poor utilization and limited rate performance of traditional MnO2 powder electrodes, obtained by pressing a mixed paste of MnO2 powder, conductive additive and polymer binder onto metallic current collectors. Developing binder-free MnO2 electrodes by loading nanoscale MnO2 deposits on pre-fabricated device-ready electrode scaffolds is an effective way to achieve both high power and energy performance. These electrode scaffolds, with interconnected skeletons and pore structures, will not only provide mechanical support and electron collection as traditional current collectors but also fast ion transfer tunnels, leading to high MnO2 utilization and rate performance. This review covers design strategies, materials and fabrication methods for the electrode scaffolds. Rational evaluation of the true performance of these electrodes is carried out, which clarifies that some of the electrodes with as-claimed exceptional performances lack potential in practical applications due to poor mass loading of MnO2 and large dead volume of inert scaffold materials/void spaces in the electrode structure. Possible ways to meet this challenge and bring MnO2 electrodes from laboratory studies to real-world applications are considered.

High Mass Loading MnO2 with Hierarchical Nanostructures for Supercapacitors.

PubMed

Huang, Zi-Hang; Song, Yu; Feng, Dong-Yang; Sun, Zhen; Sun, Xiaoqi; Liu, Xiao-Xia

2018-04-24

Metal oxides have attracted renewed interest as promising electrode materials for high energy density supercapacitors. However, the electrochemical performance of metal oxide materials deteriorates significantly with the increase of mass loading due to their moderate electronic and ionic conductivities. This limits their practical energy. Herein, we perform a morphology and phase-controlled electrodeposition of MnO 2 with ultrahigh mass loading of 10 mg cm -2 on a carbon cloth substrate to achieve high overall capacitance without sacrificing the electrochemical performance. Under optimum conditions, a hierarchical nanostructured architecture was constructed by interconnection of primary two-dimensional ε-MnO 2 nanosheets and secondary one-dimensional α-MnO 2 nanorod arrays. The specific hetero-nanostructures ensure facile ionic and electric transport in the entire electrode and maintain the structure stability during cycling. The hierarchically structured MnO 2 electrode with high mass loading yields an outstanding areal capacitance of 3.04 F cm -2 (or a specific capacitance of 304 F g -1 ) at 3 mA cm -2 and an excellent rate capability comparable to those of low mass loading MnO 2 electrodes. Finally, the aqueous and all-solid asymmetric supercapacitors (ASCs) assembled with our MnO 2 cathode exhibit extremely high volumetric energy densities (8.3 mWh cm -3 at the power density of 0.28 W cm -3 for aqueous ASC and 8.0 mWh cm -3 at 0.65 W cm -3 for all-solid ASC), superior to most state-of-the-art supercapacitors.

MnO2 Nanorods Intercalating Graphene Oxide/Polyaniline Ternary Composites for Robust High-Performance Supercapacitors

PubMed Central

Han, Guangqiang; Liu, Yun; Zhang, Lingling; Kan, Erjun; Zhang, Shaopeng; Tang, Jian; Tang, Weihua

2014-01-01

New ternary composites of MnO2 nanorods, polyaniline (PANI) and graphene oxide (GO) have been prepared by a two-step process. The 100 nm-long MnO2 nanorods with a diameter ~20 nm are conformably coated with PANI layers and fastened between GO layers. The MnO2 nanorods incorporated ternary composites electrode exhibits significantly increased specific capacitance than PANI/GO binary composite in supercapacitors. The ternary composite with 70% MnO2 exhibits a highest specific capacitance reaching 512 F/g and outstanding cycling performance, with ~97% capacitance retained over 5000 cycles. The ternary composite approach offers an effective solution to enhance the device performance of metal-oxide based supercapacitors for long cycling applications. PMID:24769835

Engineering birnessite-type MnO2 nanosheets on fiberglass for pH-dependent degradation of methylene blue

NASA Astrophysics Data System (ADS)

Xin Zhang, Yu; Long Guo, Xiao; Huang, Ming; Dong Hao, Xiao; Yuan, Yuan; Hua, Chao

2015-08-01

We construct hierarchical MnO2 nanosheets @ fiberglass nanostructures via one-pot hydrothermal method without any surfactants. The morphology and structure of MnO2-modified fiberglass composites are examined by focus ion beam scanning electron microscopy (FIB/SEM), X-Ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The birnessite-type MnO2 nanosheets are observed to grow vertically on the surface of fiberglass. Furthermore, the birnessite-type MnO2-fiberglass composites exhibit good ability for degradation of methylene blue (MB) in different pH levels. In neutral solution (pH 6.5-7.0), it achieves a high removal rate of 96.1% (2 h, at 60 °C) in the presence of H2O2; and in acidic environment (pH 1.5), 96.8% of MB solution (20 mg/L, 100 mL) is decomposed by oxidation within only 5 min. In principles, the rational design of MnO2 nanosheets-decorated fiberglass architectures demonstrated the suitability of the low-cost MnO2-modified fiberglass nanostructure for water treatment.

Preparation and the Electrochemical Performance of MnO2/PANI@CNT Composite for Supercapacitors.

PubMed

Wang, Hongjuan; Wang, Xiaohui; Peng, Cheng; Peng, Feng; Yu, Hao

2015-01-01

Polyaniline (PANI) was settled on the surface of CNTs in advance and then used as self-sacrifice reducing agent that would react with KMnO4 to prepare MnO2/PANI@CNT supercapacitor material. With PANI substituting for CNTs to participant the redox reaction, CNTs was protected from being destroyed and could maintain its original morphology and conductivity. The results of cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) show that the optimal capacitive performance can be reached at the MnO2 loading of 64.4 wt% and the pH of 1 during the deposition of MnO2. With the protective PANI, MnO2/PANI@CNT composite exhibits the superior specific capacitance of 215.8 F/g at a current density of 200 mA/g and remains 86.5% of its maximal specific capacitance at a current density of 1000 mA/g.

The Intrinsic Ferromagnetism in a MnO2 Monolayer.

PubMed

Kan, M; Zhou, J; Sun, Q; Kawazoe, Y; Jena, P

2013-10-17

The Mn atom, because of its special electronic configuration of 3d(5)4s(2), has been widely used as a dopant in various two-dimensional (2D) monolayers such as graphene, BN, silicene and transition metal dichalcogenides (TMDs). The distributions of doped Mn atoms in these systems are highly sensitive to the synthesis process and conditions, thus suffering from problems of low solubility and surface clustering. Here we show for the first time that the MnO2 monolayer, synthetized 10 years ago, where Mn ions are individually held at specific sites, exhibits intrinsic ferromagnetism with a Curie temperature of 140 K, comparable to the highest TC value achieved experimentally for Mn-doped GaAs. The well-defined atomic configuration and the intrinsic ferromagnetism of the MnO2 monolayer suggest that it is superior to other magnetic monolayer materials.

Facile synthesis of graphene-wrapped honeycomb MnO2 nanospheres and their application in supercapacitors.

PubMed

Zhu, Jiayi; He, Junhui

2012-03-01

Graphene-wrapped MnO(2) nanocomposites were first fabricated by coassembly between honeycomb MnO(2) nanospheres and graphene sheets via electrostatic interaction. The materials were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and thermogravimetric analysis. The novel MnO(2)/graphene hybrid materials were used for investigation of electrochemical capacitive behaviors. The hybrid materials displayed enhanced capacitive performance (210 F/g at 0.5 A/g). Additionally, over 82.4% of the initial capacitance was retained after repeating the cyclic voltammetry test for 1000 cycles. The improved electrochemical performance might be attributed to the combination of the pesudocapacitance of MnO(2) nanospheres with the honeycomb-like "opened" structure and good electrical conductivity of graphene sheets. © 2012 American Chemical Society

Dissimilatory Arsenate Reduction and In Situ Microbial Activities and Diversity in Arsenic-rich Groundwater of Chianan Plain, Southwestern Taiwan.

PubMed

Das, Suvendu; Liu, Chia-Chuan; Jean, Jiin-Shuh; Liu, Tsunglin

2016-02-01

Although dissimilatory arsenic reduction (DAsR) has been recognized as an important process for groundwater arsenic (As) enrichment, its characterization and association with in situ microbial activities and diversity in As-rich groundwater is barely studied. In this work, we collected As-rich groundwater at depths of 23, 300, and 313 m, respectively, from Yenshui-3, Budai-Shinwen, and Budai-4 of Chianan plain, southwestern Taiwan, and conducted incubation experiments using different electron donors, acceptors, and sulfate-reducing bacterial inhibitor (tungstate) to characterize DAsR. Moreover, bacterial diversity was evaluated using 454-pyrosequencing targeting bacterial 16S rRNAs. MPN technique was used to enumerate microorganisms with different in situ metabolic functions. The results revealed that DAsR in groundwater of Chianan plain was a biotic phenomenon (as DAsR was totally inhibited by filter sterilization), enhanced by the type of electron donor (in this case, lactate enhanced DAsR but acetate and succinate did not), and limited by the availability of arsenate. In addition to oxidative recycling of As(III), dissolution of As(V)-saturated manganese and iron minerals by indigenous dissimilatory Mn(IV)- and Fe(III)-reducing bacteria, and abiotic oxidation of As(III) with Mn(IV) regenerated As(V) in the groundwater. Sulfate-respiring bacteria contributed 7.4 and 28.2 % to the observed DAsR in groundwater of Yinshui-3 and Budai-Shinwen, respectively, whereas their contribution was negligible in groundwater of Budai-4. A noticeable variation in dominant genera Acinetobacter and Bacillus was observed within the groundwater. Firmicutes dominated in highly As-rich groundwater of Yenshui-3, whereas Proteobacteria dominated in comparatively less As-rich groundwater of Budai-Shinwen and Budai 4.

Redox exchange induced MnO2 nanoparticle enrichment in poly(3,4-ethylenedioxythiophene) nanowires for electrochemical energy storage.

PubMed

Liu, Ran; Duay, Jonathon; Lee, Sang Bok

2010-07-27

MnO2 nanoparticle enriched poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires are fabricated by simply soaking the PEDOT nanowires in potassium permanganate (KMnO4) solution. The structures of these MnO2 nanoparticle enriched PEDOT nanowires are characterized by SEM and TEM, which show that the MnO2 nanoparticles have uniform sizes and are finely dispersed in the PEDOT matrix. The chemical constituents and bonding of these composite nanowires are characterized by energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and infrared spectroscopy, which indicate that the formation and dispersion of these MnO2 nanoparticles into the nanoscale pores of the PEDOT nanowires are most likely triggered by the reduction of KMnO4 via the redox exchange of permanganate ions with the functional group on PEDOT. Varying the concentrations of KMnO4 and the reaction time controls the loading amount and size of the MnO2 nanoparticles. Cyclic voltammetry and galvanostatic charge-discharge are used to characterize the electrochemical properties of these MnO2 nanoparticle loaded PEDOT nanowires. Due to their extremely high exposed surface area with nanosizes, the pristine MnO2 nanoparticles in these MnO2 nanoparticle enriched PEDOT nanowires show very high specific capacitance (410 F/g) as the supercapacitor electrode materials as well as high Li+ storage capacity (300 mAh/g) as cathode materials of Li ion battery, which boost the energy storage capacity of PEDOT nanowires to 4 times without causing excessive volume expansion in the polymer. The highly conductive and porous PEDOT matrix facilitates fast charge/discharge of the MnO2 nanoparticles and prevents them from agglomerating. These synergic properties enable the MnO2 nanoparticle enriched PEDOT nanowires to be promising electrode materials for supercapacitors and lithium ion batteries.

MnO2-deposited lignin-based carbon nanofiber mats for application as electrodes in symmetric pseudocapacitors.

PubMed

Youe, Won-Jae; Kim, Seok Ju; Lee, Soo-Min; Chun, Sang-Jin; Kang, Juwon; Kim, Yong Sik

2018-06-01

Low-cost, high-performance electrodes are highly attractive for practical supercapacitor applications. MnO 2 -deposited carbon nanofiber mats (MnO 2 -CNFMs) are prepared for use as binder-free supercapacitor electrodes. MnO 2 is deposited on the mats in situ by hydrothermally decomposing aqueous KMnO 4 , leading to the formation of nanocrystals of MnO 2 . The MnO 2 -CNFM electrode produced with 38.0μmol KMnO 4 (this electrode) shows a high specific capacitance of ~171.6F·g -1 at a scan rate of 5mV·s -1 . Moreover, a symmetric supercapacitor with the electrode exhibits a specific capacitance of 67.0F·g -1 , an energy density of 6.0Wh·kg -1 and a power density of 160W·kg -1 at a special current of 0.1A·g -1 . Further, the symmetric supercapacitor displays excellent cycling stability, retains approximately 99% of the capacitance after 1000cycles. The simplicity and ease of preparation of the MnO 2 -CNFMs as well as their suitability for use in coin-type supercapacitor cells make them ideal for application in cost-effective and high-performance electrodes for supercapacitors. Copyright © 2018 Elsevier B.V. All rights reserved.

MnO2/multiwall carbon nanotube/Ni-foam hybrid electrode for electrochemical capacitor

NASA Astrophysics Data System (ADS)

Chen, L. H.; Li, L.; Qian, W. J.; Dong, C. K.

2018-01-01

The ternary composites of manganese dioxide/multiwall carbon nanotube/Ni-foam (MnO2/MWNT/Ni-foam) for supercapacitors were fabricated via a hydrothermal method after direct growth of MWNTs on the Ni-foam. The structural properties of the electrodes were characterized by SEM and TEM. The electrode exhibited excellent electrochemical properties from the investigation based on the three-electrode setup. Low contact resistance Rs of about 0.291 Ω between MnO2/MWNT and Ni-foam was reached benefited from the direct growth structure. High capacitance of 355.1 F/g at the current density of 2 A/g was achieved, with good capacitive response at high current density. The MnO2/MWNT/Ni-foam electrode exhibits good stability performance after 2000 cycles at a current of 40 mA.

Thermoelectric properties of Ca0.8Dy0.2MnO3 synthesized by solution combustion process

NASA Astrophysics Data System (ADS)

Park, Kyeongsoon; Lee, Ga Won

2011-10-01

High-quality Ca0.8Dy0.2MnO3 nano-powders were synthesized by the solution combustion process. The size of the synthesized Ca0.8Dy0.2MnO3 powders was approximately 23 nm. The green pellets were sintered at 1150-1300°C at a step size of 50°C. Sintered Ca0.8Dy0.2MnO3 bodies crystallized in the perovskite structure with an orthorhombic symmetry. The sintering temperature did not affect the Seebeck coefficient, but significantly affected the electrical conductivity. The electrical conductivity of Ca0.8Dy0.2MnO3 increased with increasing temperature, indicating a semiconducting behavior. The absolute value of the Seebeck coefficient gradually increased with an increase in temperature. The highest power factor (3.7 × 10-5 Wm-1 K-2 at 800°C) was obtained for Ca0.8Dy0.2MnO3 sintered at 1,250°C. In this study, we investigated the microstructure and thermoelectric properties of Ca0.8Dy0.2MnO3, depending on sintering temperature.

Thermoelectric properties of Ca0.8Dy0.2MnO3 synthesized by solution combustion process

PubMed Central

2011-01-01

High-quality Ca0.8Dy0.2MnO3 nano-powders were synthesized by the solution combustion process. The size of the synthesized Ca0.8Dy0.2MnO3 powders was approximately 23 nm. The green pellets were sintered at 1150-1300°C at a step size of 50°C. Sintered Ca0.8Dy0.2MnO3 bodies crystallized in the perovskite structure with an orthorhombic symmetry. The sintering temperature did not affect the Seebeck coefficient, but significantly affected the electrical conductivity. The electrical conductivity of Ca0.8Dy0.2MnO3 increased with increasing temperature, indicating a semiconducting behavior. The absolute value of the Seebeck coefficient gradually increased with an increase in temperature. The highest power factor (3.7 × 10-5 Wm-1 K-2 at 800°C) was obtained for Ca0.8Dy0.2MnO3 sintered at 1,250°C. In this study, we investigated the microstructure and thermoelectric properties of Ca0.8Dy0.2MnO3, depending on sintering temperature. PMID:21974984

Thermoelectric properties of Ca0.8Dy0.2MnO3 synthesized by solution combustion process.

PubMed

Park, Kyeongsoon; Lee, Ga Won

2011-10-05

High-quality Ca0.8Dy0.2MnO3 nano-powders were synthesized by the solution combustion process. The size of the synthesized Ca0.8Dy0.2MnO3 powders was approximately 23 nm. The green pellets were sintered at 1150-1300°C at a step size of 50°C. Sintered Ca0.8Dy0.2MnO3 bodies crystallized in the perovskite structure with an orthorhombic symmetry. The sintering temperature did not affect the Seebeck coefficient, but significantly affected the electrical conductivity. The electrical conductivity of Ca0.8Dy0.2MnO3 increased with increasing temperature, indicating a semiconducting behavior. The absolute value of the Seebeck coefficient gradually increased with an increase in temperature. The highest power factor (3.7 × 10-5 Wm-1 K-2 at 800°C) was obtained for Ca0.8Dy0.2MnO3 sintered at 1,250°C. In this study, we investigated the microstructure and thermoelectric properties of Ca0.8Dy0.2MnO3, depending on sintering temperature.

One-pot synthesis of MnO2-chitin hybrids for effective removal of methylene blue.

PubMed

Dassanayake, Rohan S; Rajakaruna, Erandathi; Moussa, Hanna; Abidi, Noureddine

2016-12-01

Manganese dioxide (MnO 2 )-chitin-hybrid material was prepared by a facile "one-pot" synthesis method. MnO 2 -chitin hybrid was used for the effective removal of methylene blue (MB) from liquid solution as model for wastewater treatment. The hybrid obtained was characterized by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. The effect of pH and temperature were studied. MnO 2 -chitin hybrid showed high performance for oxidative decolorization and removal of MB. Typically, 25mL of MB (20mg/L) can be completely decolorized in 2.5min with 8.5mg of the MnO 2 -chitin hybrid. The hybrid material exhibited excellent recyclability and durability with the degradation value of 99% for MB after ten consecutive cycles. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of Fe doping on the electrochemical capacitor behavior of MnO2 nanocrystals

NASA Astrophysics Data System (ADS)

Poonguzhali, R.; Shanmugam, N.; Gobi, R.; Senthilkumar, A.; Viruthagiri, G.; Kannadasan, N.

2015-10-01

In this work, the influence of Fe doping on the capacitance behavior of MnO2 nanoparticles synthesized by chemical precipitation was investigated. During the doping process the concentration of Fe was increased from 0.025 M to 0.125 M in steps of 0.025 M. The products obtained were characterized by X-ray diffraction, Fourier infrared spectroscopy, scanning electron microscopy and N2 adsorption-desorption isotherms. To demonstrate the suitability of Fe-doped MnO2 for capacitor applications, cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance were recorded. Among the different levels of doping, the specific capacitance of 912 F/g was delivered by 0.075 M of Fe-doped MnO2 at a scan rate of 10 mV/s, which is almost more than fourfold that of the bare MnO2 electrode (210 F/g). Moreover, for the same concentration the charge, discharge studies revealed the highest specific capacitance of 1084 F/g at a current density of 10 A/g.

Dual-Readout Immunochromatographic Assay by Utilizing MnO2 Nanoflowers as the Unique Colorimetric/Chemiluminescent Probe.

PubMed

Ouyang, Hui; Lu, Qian; Wang, Wenwen; Song, Yang; Tu, Xinman; Zhu, Chengzhou; Smith, Jordan N; Du, Dan; Fu, Zhifeng; Lin, Yuehe

2018-04-17

Manganese dioxide nanoflowers (MnO 2 NFs) were synthesized and used as a dual readout probe to develop a novel immunochromatographic test strip (ITS) for detecting pesticide residues using chlorpyrifos as the model analyte. MnO 2 NFs-labeled antibody for chlorpyrifos was employed as the signal tracer for conducting the ITS. After 10 min competitive immunoreaction, the tracer antibody was captured by the immobilized immunogen in the test strip, resulting in the captured MnO 2 NFs on test line. The captured MnO 2 NFs led to the appearance of brown color on the test line, which could be easily observed by the naked eye as a qualitative readout. Due to the very slight colorimetric difference of chlorpyrifos at trace concentrations, the semiquantitative readout by naked eyes could not meet the demand of quantitative analysis. MnO 2 NFs showed a significant effect on the luminol-H 2 O 2 chemiluminescent (CL) system, and the CL signal driven by MnO 2 NFs were used to detect the trace concentration of chlorpyrifos quantitatively. 1,3-Diphenylisobenzofuran quenching studies and TMB-H 2 O 2 coloration assays were conducted for studying the enhancing mechanism of MnO 2 NFs, which was based on the oxidant activity to decompose H 2 O 2 for forming reactive oxygen species. Under optimal conditions, the linear range of chlorpyrifos was 0.1-50 ng/mL with a low detection limit of 0.033 ng/mL (S/N = 3). The reliability of the dual-readout ITS was successfully demonstrated by the application on traditional Chinese medicine and environmental water samples. Due to the simultaneous rapid-qualitative and sensitive-quantitative detection, the dual-readout protocol provides a promising strategy for rapid screening and field assay on various areas such as environmental monitoring and food safety.

Identification of a c-Type Cytochrome Specific for Manganese Dioxide (MnO2) Reduction in Anaeromyxobacter dehalogenans Strain 2CP-C

NASA Astrophysics Data System (ADS)

Pfiffner, S. M.; Nissen, S.; Liu, X.; Chourey, K.; Vishnivetskaya, T. A.; Hettich, R.; Loeffler, F.

2014-12-01

Anaeromyxobacter dehalogenans is a metabolically versatile Deltaproteobacterium and conserves energy from the reduction of various electron acceptors, including insoluble MnO2 and ferric oxides/oxyhydroxides (FeOOH). The goal of this study was to identify c-type cytochromes involved in electron transfer to MnO2. The characterization of deletion mutants has revealed a number of c-type cytochromes involved in electron transfer to solid metal oxides in Shewanella spp. and Geobacter spp; however, a genetic system for Anaeromyxobacter is not available. The A. dehalogenans str. 2CP-C genome encodes 68 putative c-type cytochromes, which all lack functional assignments. To identify c-type cytochromes involved in electron transfer to solid MnO2, protein expression profiles of A. dehalogenans str. 2CP-C cells grown with acetate as electron donor and MnO2, ferric citrate, FeOOH, nitrate or fumarate as electron acceptors were compared. Whole cell proteomes were analyzed after trypsin proteolysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Distinct c-type cytochrome expression patterns were observed with cells grown with different electron acceptors. A. dehalogenans str. 2CP-C grown with MnO2 expressed 25 out of the 68 c-type cytochromes encoded on the genome. The c-type cytochrome Adeh_1278 was only expressed in strain 2CP-C grown with MnO2. Reverse transcription PCR confirmed that the Adeh_1278 gene was transcribed in MnO2-grown cells but not in cells grown with other terminal electron acceptors. The expression of the Adeh_1278 gene correlated with Mn(IV) reduction activity. Adeh_1278 has three heme binding motifs and is predicted to be located in the periplasm. The identification of Adeh_1278 as a protein uniquely expressed when MnO2 serves as electron acceptor suggests its utility as a biomarker for MnO2 reduction. This example demonstrates the value of the LC-MS/MS approach for identifying specific proteins of interest and making functional assignments

Scalable Synthesis of Triple-Core-Shell Nanostructures of TiO2 @MnO2 @C for High Performance Supercapacitors Using Structure-Guided Combustion Waves.

PubMed

Shin, Dongjoon; Shin, Jungho; Yeo, Taehan; Hwang, Hayoung; Park, Seonghyun; Choi, Wonjoon

2018-03-01

Core-shell nanostructures of metal oxides and carbon-based materials have emerged as outstanding electrode materials for supercapacitors and batteries. However, their synthesis requires complex procedures that incur high costs and long processing times. Herein, a new route is proposed for synthesizing triple-core-shell nanoparticles of TiO 2 @MnO 2 @C using structure-guided combustion waves (SGCWs), which originate from incomplete combustion inside chemical-fuel-wrapped nanostructures, and their application in supercapacitor electrodes. SGCWs transform TiO 2 to TiO 2 @C and TiO 2 @MnO 2 to TiO 2 @MnO 2 @C via the incompletely combusted carbonaceous fuels under an open-air atmosphere, in seconds. The synthesized carbon layers act as templates for MnO 2 shells in TiO 2 @C and organic shells of TiO 2 @MnO 2 @C. The TiO 2 @MnO 2 @C-based electrodes exhibit a greater specific capacitance (488 F g -1 at 5 mV s -1 ) and capacitance retention (97.4% after 10 000 cycles at 1.0 V s -1 ), while the absence of MnO 2 and carbon shells reveals a severe degradation in the specific capacitance and capacitance retention. Because the core-TiO 2 nanoparticles and carbon shell prevent the deformation of the inner and outer sides of the MnO 2 shell, the nanostructures of the TiO 2 @MnO 2 @C are preserved despite the long-term cycling, giving the superior performance. This SGCW-driven fabrication enables the scalable synthesis of multiple-core-shell structures applicable to diverse electrochemical applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-supported supercapacitor membrane through incorporating MnO2 nanowires into carbon nanotube networks.

PubMed

Fang, Yueping; Liu, Jianwei; Li, Jun

2010-08-01

We report on a study on the development of a self-supported membrane of carbon nanotube (CNT) mixed with MnO2 nanowires as supercapacitors. Both single-walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs) have been explored to serve as the electrically conductive networks to connect redox active MnO2 nanowires. High-quality alpha-MnO2 nanowires were synthesized using bulk alpha-MnO2 crystals as the precursor by a facile hydrothermal method. The morphology and structure of the as-prepared alpha-MnO2 nanowires were characterized by X-ray and electron diffraction, transmission electron microscopy, and scanning electron microscopy. Supercapacitor membranes were prepared by filtration of mixture solutions of MnO2 nanowires and CNTs at various ratios, forming entangled networks which are self-supported and directly used as supercapacitor electrodes without binders or backing metals. Cyclic voltammetry at various scan rates and charge--discharging measurements are used to characterize the supercapacitance of the CNT-MnO2 nanowire membranes. The specific capacitance has been found to be increased by several times over that of pure CNT membranes after incorporation of MnO2 nanowires.

The Influence of Layer Thickness-Ratio on Magnetoresistance in La2/3Ca1/3MnO3/La1/3Ca2/3MnO3 Exchange Biased System

NASA Astrophysics Data System (ADS)

Gomez, Maria Elena; Milena Diez, Sandra; Cuartas, Lina Maria; Marin, Lorena; Prieto, Pedro

2012-02-01

Isothermal magnetic field dependence of the resistance in La2/3Ca1/3MnO3 (F-LCMO)/ La1/3Ca2/3MnO3(AF-LCMO) bilayer and AF-LCMO/F-LCMO/AF-LCMO trilayer at temperatures below N'eel temperature of the antiferromagnetic layer were carried out to study the thickness layers influence on magneto transport properties. We grew multilayers using a high oxygen pressure sputtering technique. We systematically varied the thickness of the F-LCMO layer, tF, maintaining constant the thickness of the AF-LCMO layer, tAF. We studied the influence of the thickness ratio tF/tAF on the ZFC and FC magnetoresistance (MR) loops. HFC was varied from 100 Oe to 400 Oe. We found that MR has hysteretic behavior as observed in [La2/3Ca1/3MnO3/La1/3Ca2/3MnO3]N superlattices, where MR increases with the increasing field from H=0 to a maximum and then it decreases continuously. The position and magnitude of the maximum is not symmetric with respect to the axis H=0 for both FC and ZFC loops. We found that magnetoresistance behavior of the bilayer and trilayer is thickness-ratio dependent for both ZFC and FC loops.

Study of electrochemical reduced graphene oxide and MnO2 heterostructure for supercapacitor application

NASA Astrophysics Data System (ADS)

Jana, S. K.; Rao, V. P.; Banerjee, S.

2013-02-01

In this paper we have shown enhanced supercapacitive property of electrochemically reduced graphene oxide (ERGO) and manganese dioxide (MnO2) based heterostructure over single MnO2 thin film grown by electrochemical deposition on indium tin oxide (ITO). ERGO improves the electrical conduction leading to decrease of the internal resistance of the heterostructure.

A highly sensitive hydrogen peroxide amperometric sensor based on MnO2-modified vertically aligned multiwalled carbon nanotubes.

PubMed

Xu, Bin; Ye, Min-Ling; Yu, Yu-Xiang; Zhang, Wei-De

2010-07-26

In this report, a highly sensitive amperometric sensor based on MnO(2)-modified vertically aligned multiwalled carbon nanotubes (MnO(2)/VACNTs) for determination of hydrogen peroxide (H(2)O(2)) was fabricated by electrodeposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometer and X-ray diffraction. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were applied to investigate the electrochemical properties of the MnO(2)/VACNTs nanocomposite electrode. The mechanism for the electrochemical reaction of H(2)O(2) at the MnO(2)/VACNTs nanocomposite electrode was also discussed. In borate buffer (pH 7.8, 0.20 M), the MnO(2)/VACNTs nanocomposite electrode exhibits a linear dependence (R=0.998) on the concentration of H(2)O(2) from 1.2 x 10(-6)M to 1.8 x 10(-3)M, a high sensitivity of 1.08 x 10(6) microA M(-1) cm(-2) and a detection limit of 8.0 x 10(-7) M (signal/noise=3). Meanwhile, the MnO(2)/VACNTs nanocomposite electrode is also highly resistant towards typical inorganic salts and some biomolecules such as acetic acid, citric acid, uric acid and D-(+)-glucose, etc. In addition, the sensor based on the MnO(2)/VACNTs nanocomposite electrode was applied for the determination of trace of H(2)O(2) in milk with high accuracy, demonstrating its potential for practical application. Copyright 2010 Elsevier B.V. All rights reserved.

Capture and release of cancer cells using electrospun etchable MnO2 nanofibers integrated in microchannels

NASA Astrophysics Data System (ADS)

Liu, Hui-qin; Yu, Xiao-lei; Cai, Bo; You, Su-jian; He, Zhao-bo; Huang, Qin-qin; Rao, Lang; Li, Sha-sha; Liu, Chang; Sun, Wei-wei; Liu, Wei; Guo, Shi-shang; Zhao, Xing-zhong

2015-03-01

This paper introduces a cancer cell capture/release microchip based on the self-sacrificed MnO2 nanofibers. Through electrospinning, lift-off and soft-lithography procedures, MnO2 nanofibers are tactfully fabricated in microchannels to implement enrichment and release of cancer cells in liquid samples. The MnO2 nanofiber net which mimics the extra cellular matrix can lead to high capture ability with the help of a cancer cell-specific antibody bio-conjugation. Subsequently, an effective and friendly release method is carried out by using low concentration of oxalic acid to dissolve the MnO2 nanofiber substrate while keeping high viability of those released cancer cells at the same time. It is conceivable that our microchip may have potentials in realizing biomedical analysis of circulating tumor cells for biological and clinical researches in oncology.

Synthesis, structural, dielectric and magnetic properties of CuFe2O4/MnO2 nanocomposites

NASA Astrophysics Data System (ADS)

Ali, Kashif; Bahadur, Ali; Jabbar, Abdul; Iqbal, Shahid; Ahmad, Ijaz; Bashir, Muhammad Imran

2017-07-01

Novel nanocomposite of (1-x)CuFe2O4/xMnO2 [x=10% to 50 wt%] has been synthesized by two step wet chemical route without impurity. The x-ray diffraction analysis shows the formation of both phases with crystallite size 40-100 nm which is consist ant with estimated size of SEM.The FTIR spectra confirms the characteristics vibration of ferrites atoms at tetrahedral and octahedral sites along with Mn-O vibration mode, which also confirms the coexistence of both phases. The dielectric properties studied by LCR meter in frequency range of 1 K Hz to 2 MHz.The dielectric constant and tangent loss shows same dispersion of ferrites while a.c. conductivity decreases with increase in MnO2 contents. The real and imaginary part of impedance also calculated which shows decreasing trend at higher frequency. The magnetic characterization performed by vibrating sample magnetometer (VSM) at room temperature, which shows normal ferromagnetic behavior of ferrites but saturation magnetization and coercivity decreases with incorporation of MnO2 contents.

Fabrication of Na0.7MnO2/C composite cathode material by simple heat treatment for high-power na-ion batteries

NASA Astrophysics Data System (ADS)

Sohn, DongRak; Lim, Sung-Jin; Nam, Do-Hwan; Hong, Kyung-Sik; Kim, Tae-Hee; Oh, SeKwon; Eom, Ji-Yong; Cho, EunAe; Kwon, HyukSang

2018-01-01

A Na0.7MnO2/C composite cathode material is synthesized by simple and costeffective two-step heat treatment for an improvement in the rate capability of Na0.7MnO2. The first heat treatment is to synthesize Na0.7MnO2, and the second one is a low temperature annealing at 350 °C for 1 h in air, which is necessary to suppress an interfacial reaction between the Na0.7MnO2 and C in the synthesis process of Na0.7MnO2/C composite. Structural analyses by XRD and XPS reveal that the Na0.7MnO2/C shows the same structural properties as that of the pristine Na0.7MnO2, and hence they exhibit the same initial discharge capacity of 175 mAh g-1 at 20 mA g-1. At a current density of 400 mA g-1, the discharge capacity of Na0.7MnO2 reduces to 50 mAh g-1 (28% of the initial discharge capacity), whereas that of Na0.7MnO2/C reduces to 108 mAh g-1 (61% of the initial discharge capacity). The enhanced rate capability of the Na0.7MnO2/C is attributed to the conductive carbon layer formed on the surface of Na0.7MnO2 particles, enabling the facile transport of electrons from the current collector to the surface of the Na0.7MnO2 particles. [Figure not available: see fulltext.

MnO2 prepared by hydrothermal method and electrochemical performance as anode for lithium-ion battery.

PubMed

Feng, Lili; Xuan, Zhewen; Zhao, Hongbo; Bai, Yang; Guo, Junming; Su, Chang-Wei; Chen, Xiaokai

2014-01-01

Two α-MnO2 crystals with caddice-clew-like and urchin-like morphologies are prepared by the hydrothermal method, and their structure and electrochemical performance are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), galvanostatic cell cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The morphology of the MnO2 prepared under acidic condition is urchin-like, while the one prepared under neutral condition is caddice-clew-like. The identical crystalline phase of MnO2 crystals is essential to evaluate the relationship between electrochemical performances and morphologies for lithium-ion battery application. In this study, urchin-like α-MnO2 crystals with compact structure have better electrochemical performance due to the higher specific capacity and lower impedance. We find that the relationship between electrochemical performance and morphology is different when MnO2 material used as electrochemical supercapacitor or as anode of lithium-ion battery. For lithium-ion battery application, urchin-like MnO2 material has better electrochemical performance.

Nucleation and Growth of Porous MnO2 Coatings Prepared on Nickel Foam and Evaluation of Their Electrochemical Performance

PubMed Central

Huang, Wenxin; Li, Jun; Xu, Yunhe

2018-01-01

Porous MnO2 was uniformly electrodeposited on nickel foam in MnSO4 solution, which was applied as the electrode of supercapacitors. The nucleation/growth mechanisms of porous MnO2 were investigated firstly. Then two kinds of electrochemical measuring technologies, corresponding to the cycle voltammetry (CV) and galvanostatic charge-discharge, were adopted to assess the electrochemical performance of MnO2 electrodes. The results demonstrated that the deposition of MnO2 on nickel foam included four stages. Prior to the deposition, an extremely short incubation period of about 2 s was observed (the first stage). Then the exposed nickel foam was instantly covered by a large number of MnO2 crystal nuclei and crystal nuclei connected with each other in a very short time of about 3 s (the second stage). Nucleation predominated in the second stage. The sharply rise of current was caused by the increase in substrate surface area which due to nucleation of MnO2. Grain boundaries grew preferentially due to their high energy, accompanied with a honeycomb-like structure with the higher surface area was formed. However, accompanied with the electrochemical reactions gradually diffusion-controlled, the current presented the decline trend with increasing the time (the third stage). When the electrochemical reactions were completely diffusion-controlled, the porous MnO2 coating with an approximately constant surface area was formed (the fourth stage). MnO2 coatings deposited for different time (30, 60, 120, 300 s) exhibited a similar specific capacitance (CV: about 224 F/g; galvanostatic charge-discharge: about 264 F/g). Comparatively speaking, the value of MnO2 deposited for 600 s was highest (CV: 270 F/g; galvanostatic charge-discharge: 400 F/g). PMID:29724063

Self-Assembly of Mesoporous Nanotubes Assembled from Interwoven Ultrathin Birnessite-type MnO2 Nanosheets for Asymmetric Supercapacitors

PubMed Central

Huang, Ming; Zhang, Yuxin; Li, Fei; Zhang, Lili; Ruoff, Rodney S.; Wen, Zhiyu; Liu, Qing

2014-01-01

Porous nanotubes comprised of MnO2 nanosheets were fabricated with a one-pot hydrothermal method using polycarbonate membrane as the template. The diameter and thickness of nanotubes can be controlled by choice of the membrane pore size and the chemistry. The porous MnO2 nanotubes were used as a supercapacitor electrode. The specific capacitance in a three-electrode system was 365 F g−1 at a current density of 0.25 A g−1 with capacitance retention of 90.4% after 3000 cycles. An asymmetric supercapacitor with porous MnO2 nanotubes as the positive electrode and activated graphene as the negative electrode yielded an energy density of 22.5 Wh kg−1 and a maximum power density of 146.2 kW kg−1; these values exceeded those reported for other MnO2 nanostructures. The supercapacitor performance was correlated with the hierarchical structure of the porous MnO2 nanotubes. PMID:24464344

Dual-Readout Immunochromatographic Assay by Utilizing MnO 2 Nanoflowers as the Unique Colorimetric/Chemiluminescent Probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouyang, Hui; Lu, Qian; Wang, Wenwen

Manganese dioxide nanoflowers (MnO2 NFs) were synthesized and utilized as a dual readout probe to develop a novel immunochromatographic test strip (ITS) for detecting pesticide residues using chlorpyrifos as the model analyte. MnO2 NFs-labeled antibody for chlorpyrifos was employed as the signal tracer for conducting the ITS. After 10-min competitive immunoreaction, the tracer antibody was captured by the immobilized immunogen on test line in the test strip, resulting in the accumulation of MnO2 NFs. The accumulation of MnO2 NFs led to the appearance of brown color on the test line, which could be easily observed by the naked eye asmore » a qualitative readout. Moreover, MnO2 NFs showed a remarkably enhancing effect on the luminol-H2O2 chemiluminescent (CL) system. Unlike peroxidase-like nanomaterials, the enhancing mechanism of MnO2 NFs was based on its oxidant activity to decompose H2O2 for forming reactive oxygen species. After initiating the CL system in the test zone, strong CL signal was collected as a quantitative readout to sensitively detect chlorpyrifos. Under optimal conditions, the linear range of chlorpyrifos was 0.1–50 ng/mL with a low detection limit of 0.033 ng/mL (S/N = 3). The reliability of the dual-readout ITS was successfully demonstrated by the application on traditional Chinese medicine and environmental water samples. Due to the simultaneous rapid-qualitative and sensitive-quantitative detection, the dual-readout protocol provides a promising strategy for rapid screening and field assay on various areas such as environmental monitoring, food safety and point-of-care testing.« less

Preparation of PPy-Coated MnO2 Hybrid Micromaterials and Their Improved Cyclic Performance as Anode for Lithium-Ion Batteries

NASA Astrophysics Data System (ADS)

Feng, Lili; Zhang, Yinyin; Wang, Rui; Zhang, Yanli; Bai, Wei; Ji, Siping; Xuan, Zhewen; Yang, Jianhua; Zheng, Ziguang; Guan, Hongjin

2017-09-01

MnO2@PPy core-shell micromaterials are prepared by chemical polymerization of pyrrole on the MnO2 surface. The polypyrrole (PPy) is formed as a homogeneous organic shell on the MnO2 surface. The thickness of PPy shell can be adjusted by the usage of pyrrole. The analysis of SEM, FT-IR, X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), and XRD are used to confirm the formation of PPy shell. Galvanostatic cell cycling and electrochemical impedance spectroscopy (EIS) are used to evaluate the electrochemical performance as anode for lithium-ion batteries. The results show that after formation of MnO2@PPy core-shell micromaterials, the cyclic performance as anode for lithium-ion batteries is improved. Fifty microliters of PPy-coated caddice-clew-like MnO2 has the best cyclic performances as has 620 mAh g-1 discharge specific capacities after 300 cycles. As a comparison, the discharge specific capacity of bare MnO2 materials falls to below 200 mAh g-1 after 10 cycles. The improved lithium-storage cyclic stability of the MnO2@PPy samples attributes to the core-shell hybrid structure which can buffer the structural expansion and contraction of MnO2 caused by the repeated embedding and disengagement of Li ions and can prevent the pulverization of MnO2. This experiment provides an effective way to mitigate the problem of capacity fading of the transition metal oxide materials as anode materials for (lithium-ion batteries) LIBs.

Preparation of PPy-Coated MnO2 Hybrid Micromaterials and Their Improved Cyclic Performance as Anode for Lithium-Ion Batteries.

PubMed

Feng, Lili; Zhang, Yinyin; Wang, Rui; Zhang, Yanli; Bai, Wei; Ji, Siping; Xuan, Zhewen; Yang, Jianhua; Zheng, Ziguang; Guan, Hongjin

2017-09-02

MnO 2 @PPy core-shell micromaterials are prepared by chemical polymerization of pyrrole on the MnO 2 surface. The polypyrrole (PPy) is formed as a homogeneous organic shell on the MnO 2 surface. The thickness of PPy shell can be adjusted by the usage of pyrrole. The analysis of SEM, FT-IR, X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), and XRD are used to confirm the formation of PPy shell. Galvanostatic cell cycling and electrochemical impedance spectroscopy (EIS) are used to evaluate the electrochemical performance as anode for lithium-ion batteries. The results show that after formation of MnO 2 @PPy core-shell micromaterials, the cyclic performance as anode for lithium-ion batteries is improved. Fifty microliters of PPy-coated caddice-clew-like MnO 2 has the best cyclic performances as has 620 mAh g -1 discharge specific capacities after 300 cycles. As a comparison, the discharge specific capacity of bare MnO 2 materials falls to below 200 mAh g -1 after 10 cycles. The improved lithium-storage cyclic stability of the MnO 2 @PPy samples attributes to the core-shell hybrid structure which can buffer the structural expansion and contraction of MnO 2 caused by the repeated embedding and disengagement of Li ions and can prevent the pulverization of MnO 2 . This experiment provides an effective way to mitigate the problem of capacity fading of the transition metal oxide materials as anode materials for (lithium-ion batteries) LIBs.

Encapsulation of superparamagnetic Fe 3 O 4 @SiO 2 core/shell nanoparticles in MnO 2 microflowers with high surface areas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yu-Gang; Truong, Tu T.; Liu, Yu-Zi

2015-02-01

Microflowers made of interconnected MnO2 nanosheets have been successfully synthesized in a microwave reactor through a hydrothermal reduction of KMnO4 with aqueous HCl at elevated temperatures in the presence of superparamagnetic Fe3O4@SiO2 core-shell nanoparticles. Due to the chemical compatibility between SiO2 and MnO2, the heterogeneous reaction leads to the spontaneous encapsulation of the Fe3O4@SiO2 core-shell nanoparticles in the MnO2 microflowers. The resulting hybrid particles exhibit multiple properties including high surface area associated with the MnO2 nanosheets and superparamagnetism originated from the Fe3O4@SiO2 core-shell nanoparticles, which are beneficial for applications requiring both high surface area and magnetic separation. (C) 2014 Yu-Gangmore » Sun.« less

Structural and dielectric characteristics of double perovskite La2(NiFe)1/2MnO6

NASA Astrophysics Data System (ADS)

Nasir, Mohd.; Kandasami, Asokan; Sen, Somaditya

2018-05-01

Recently, La2NiMnO6 has drawn significant interest because large magnetic field induced changes in dielectric properties makes this compound a promising material for potential spintronic device applications. In the present study, the structural and dielectric characteristics of sol-gel prepared La2(Ni1/2Fe1/2)MnO6 double perovskite ceramics were evaluated. La2(Ni1/2Fe1/2)MnO6 was crystallized in the monoclinic P21/n structure with ordered Ni2+/Fe2+ and Mn4+ cations. A giant dielectric constant with relaxor-like behavior was observed, which was attributed to the dipolar effects arising from hopping between Ni2+/Fe2+ and Mn4+ ions.

An Effective Electrodeposition Mode for Porous MnO2/Ni Foam Composite for Asymmetric Supercapacitors

PubMed Central

Tsai, Yi-Chiun; Yang, Wein-Duo; Lee, Kuan-Ching; Huang, Chao-Ming

2016-01-01

Three kinds of MnO2/Ni foam composite electrode with hierarchical meso-macroporous structures were prepared using potentiodynamic (PD), potentiostatic (PS), and a combination of PS and PD(PS + PD) modes of electrodeposition. The electrodeposition mode markedly influenced the surface morphological, textural, and supercapacitive properties of the MnO2/Ni electrodes. The supercapacitive performance of the MnO2/Ni electrode obtained via PS + PD(PS + PD(MnO2/Ni)) was found to be superior to those of MnO2/Ni electrodes obtained via PD and PS, respectively. Moreover, an asymmetric supercapacitor device, activated carbon (AC)/PS + PD(MnO2/Ni), utilizing PS + PD(MnO2/Ni) as a positive electrode and AC as a negative electrode, was fabricated. The device exhibited an energy density of 7.7 Wh·kg−1 at a power density of 600 W·kg−1 and superior cycling stability, retaining 98% of its initial capacity after 10,000 cycles. The good supercapacitive performance and excellent stability of the AC/PS + PD(MnO2/Ni) device can be ascribed to its high surface area, hierarchical structure, and interconnected three-dimensional reticular configuration of the nickel metal support, which facilitates electrolyte ion intercalation and deintercalation at the electrode/electrolyte interface and mitigates volume change during repeated charge/discharge cycling. These results demonstrate the great potential of the combination of PS and PD modes for MnO2 electrodeposition for the development of high-performance electrodes for supercapacitors. PMID:28773371

MnO2 Nanowire/Biomass-Derived Carbon from Hemp Stem for High-Performance Supercapacitors.

PubMed

Yang, MinHo; Kim, Dong Seok; Hong, Seok Bok; Sim, Jae-Wook; Kim, Jinsoo; Kim, Seung-Soo; Choi, Bong Gill

2017-05-30

Hierarchical 3D nanostructures based on waste biomass are being offered as promising materials for energy storage due to their processabilities, multifunctionalities, environmental benignities, and low cost. Here we report a facile, inexpensive, and scalable strategy for the fabrication of hierarchical porous 3D structure as electrode materials for supercapacitors based on MnO 2 nanowires and hemp-derived activated carbon (HC). Vertical MnO 2 wires are uniformly deposited onto the surface of HC using a one-step hydrothermal method to produce hierarchical porous structures with conductive interconnected 3D networks. HC acts as a near-ideal 3D current collector and anchors electroactive materials, and this confers a specific capacitance of 340 F g -1 at 1 A g -1 with a high rate capability (88% retention) of the 3D MnO 2 /HC composite because of its open-pore system, which facilitates ion and electron transports and synergistic contribution of two energy-storage materials. Moreover, asymmetric supercapacitors fabricated using 3D HC as the anode and 3D MnO 2 /HC as the cathode are able to store 33.3 Wh kg -1 of energy and have a power delivery of 14.8 kW kg -1 .

Mesoporous MnO2/carbon aerogel composites as promising electrode materials for high-performance supercapacitors.

PubMed

Li, Gao-Ren; Feng, Zhan-Ping; Ou, Yan-Nan; Wu, Dingcai; Fu, Ruowen; Tong, Ye-Xiang

2010-02-16

MnO(2) as one of the most promising candidates for electrochemical supercapacitors has attracted much attention because of its superior electrochemical performance, low cost, and environmentally benign nature. In this Letter, we explored a novel route to prepare mesoporous MnO(2)/carbon aerogel composites by electrochemical deposition assisted by gas bubbles. The products were characterized by energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The MnO(2) deposits are found to have high purity and have a mesoporous structure that will optimize the electronic and ionic conductivity to minimize the total resistance of the system and thereby maximize the performance characteristics of this material for use in supercapacitor electrodes. The results of nitrogen adsorption-desorption experiments and electrochemical measurements showed that these obtained mesoporous MnO(2)/carbon aerogel composites had a large specific surface area (120 m(2)/g), uniform pore-size distribution (around 5 nm), high specific capacitance (515.5 F/g), and good stability over 1000 cycles, which give these composites potential application as high-performance supercapacitor electrode materials.

Improved supercapacitor performance of MnO2-electrospun carbon nanofibers electrodes by mT magnetic field

NASA Astrophysics Data System (ADS)

Zeng, Zheng; Liu, Yiyang; Zhang, Wendi; Chevva, Harish; Wei, Jianjun

2017-08-01

This work reports on a finding of mT magnetic field induced energy storage enhancement of MnO2-based supercapacitance electrodes (magneto-supercapacitor). Electrodes with MnO2 electrochemically deposited at electrospun carbon nanofibers (ECNFs) film are studied by cyclic voltammetry (CV), galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS), and life cycle stability tests in the presence/absence of milli-Tesla (mT) magnetic fields derived by Helmholtz coils. In the presence of a 1.34 mT magnetic field, MnO2/ECNFs shows a magneto-enhanced capacitance of 141.7 F g-1 vs. 119.2 F g-1 (∼19% increase) with absence of magnetic field at a voltage sweeping rate of 5 mV s-1. The mechanism of the magneto-supercapacitance is discussed and found that the magnetic susceptibility of the MnO2 significantly improves the electron transfer of a pseudo-redox reaction of Mn(IV)/Mn(III) at the electrode, along with the magnetic field induced impedance effect, which may greatly enhance the interface charge density, facilitate electrolyte transportation, and improve the efficiency of cation intercalation/de-intercalation of the pseudocapacitor under mT-magnetic field exposure, resulting in enhancement of energy storage capacitance and longer charge/discharge time of the MnO2/ECNFs electrode without sacrificing its life cycle stability.

MnO2 prepared by hydrothermal method and electrochemical performance as anode for lithium-ion battery

PubMed Central

2014-01-01

Two α-MnO2 crystals with caddice-clew-like and urchin-like morphologies are prepared by the hydrothermal method, and their structure and electrochemical performance are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), galvanostatic cell cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The morphology of the MnO2 prepared under acidic condition is urchin-like, while the one prepared under neutral condition is caddice-clew-like. The identical crystalline phase of MnO2 crystals is essential to evaluate the relationship between electrochemical performances and morphologies for lithium-ion battery application. In this study, urchin-like α-MnO2 crystals with compact structure have better electrochemical performance due to the higher specific capacity and lower impedance. We find that the relationship between electrochemical performance and morphology is different when MnO2 material used as electrochemical supercapacitor or as anode of lithium-ion battery. For lithium-ion battery application, urchin-like MnO2 material has better electrochemical performance. PMID:24982603

Highly conductive three-dimensional MnO2-carbon nanotube-graphene-Ni hybrid foam as a binder-free supercapacitor electrode.

PubMed

Zhu, Guoyin; He, Zhi; Chen, Jun; Zhao, Jin; Feng, Xiaomiao; Ma, Yanwen; Fan, Quli; Wang, Lianhui; Huang, Wei

2014-01-21

Carbon nanotube (CNT)-graphene hybrids grown on porous Ni foam are used as substrates to immobilize MnO2 nanoflakes, thus forming three-dimensional (3D) MnO2-CNT-graphene-Ni hybrid foam. The as-prepared hybrid materials could be used as supercapacitor electrodes directly without any binder and conductive additives, and fully maintain the high conductivity and high surface-to-volume ratio of CNTs, large pseudocapacitance of MnO2 nanoflakes and high porosity provided by the framework of Ni foam. The conductivity of the 3D MnO2-CNT-graphene-Ni foam is as high as 117 S cm(-1) due to the seamless integration of MnO2 nanoflakes, CNTs, graphene and Ni foam among the 3D frameworks, which guarantee its low internal resistance (1.25 ohm) when compacted into supercapacitor devices. In aqueous electrolytes, the 3D MnO2-CNT-graphene-Ni based prototype supercapacitors show specific capacitances of ~251 F g(-1) with good cycling stability at a current density of 1.0 A g(-1). In addition, these 3D hybrids also demonstrate their potential in all-solid-state flexible supercapacitors.

Sulfide as a Chemoautotrophic Electron Donor for Dissimilatory Arsenate Reduction in Mono Lake, California

NASA Astrophysics Data System (ADS)

Hoeft, S. E.; Kulp, T. R.; Stolz, J. S.; Oremland, R. S.

2003-12-01

In aqueous systems, arsenic occurs as arsenate [As(V)] or as arsenite [As(III)], with the latter form being more toxic and mobile. Mono Lake, California is a meromictic soda lake (pH = 9.8; salinity = 70-90 g/L) with exceptionally high arsenic content ( ˜200 μ M), a consequence of hydrothermal inputs combined with evaporative concentration. Previous work has shown that arsenic speciation changes from As(V) to the more reduced As(III) with vertical transition from the lake's surface oxic waters to its unmixed, anoxic bottom waters and that dissimilatory reduction is responsible for the observed change in arsenic speciation. Rates of in situ dissimilatory As(V) reduction measured by radiotracer ( ˜1- 6 μ mol/L/d) were estimated to be significant enough to mineralize up to 14% of annual primary productivity. Subsequent lab-based investigations with As(V)-amended ( ˜1-2 mM) bottom water displayed significantly higher rates (150-260 μ mol/L/d) of As(V) reduction and were not limited by the availability of organic electron donors such as acetate, lactate, malate and glucose. The focus of this study was to identify a natural source of electrons for As(V) reduction in Mono Lake. While Mono Lake contains plentiful dissolved organic carbon ( ˜7 mM) this material is usually refractory and resistant to bacterial oxidation. Alternatively, the anoxic bottom waters contain high concentrations of sulfide ions ( ˜1-2 mM) that could potentially serve as an electron donor for dissimilatory As(V) reduction. In a time course experiment with As(V)-amended Mono Lake bottom water, we observed oxidation of sulfide linked to the reduction of As(V) to As(III). This reaction did not occur in filter sterilized controls and sulfide loss did not occur in samples lacking As(V). In bottom water amended with additional sulfide (total = 6 mM) and As(V), we observed a linear relationship between rates of dissimilatory As(V) reduction and As(V) concentration. The highest rate observed under

Three-dimensional ordered macroporous MnO2/carbon nanocomposites as high-performance electrodes for asymmetric supercapacitors.

PubMed

Yang, Chunzhen; Zhou, Ming; Xu, Qian

2013-12-07

MnO2/carbon composites with ultrathin MnO2 nanofibers (diameter of 5-10 nm) uniformly deposited on three dimensional ordered macroporous (3DOM) carbon frameworks were fabricated via a self-limiting redox process. The MnO2 nanofibers provide a large surface area for charge storage, whereas the 3DOM carbon serves as a desirable supporting material providing rapid ion and electron transport through the composite electrodes. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) were used to characterize the capacitive performance of these composites. Optimization of the composition results in a composite with 57 wt% MnO2 content, which gives both a high specific capacitance (234 F g(-1) at a discharge current of 0.1 A g(-1)) and good rate capability (52% retention of the capacitance at 5 A g(-1)). An asymmetric supercapacitor was fabricated by assembling the optimized MnO2/carbon composite as the positive electrode and 3DOM carbon as the negative electrode. The asymmetric supercapacitor exhibits superior electrochemical performances, which can be reversibly charged and discharged at a maximum cell voltage of 2.0 V in 1.0 M Na2SO4 aqueous electrolyte, delivering both high energy density (30.2 W h kg(-1)) and power density (14.5 kW kg(-1)). Additionally, the asymmetric supercapacitor exhibits an excellent cycle life, with 95% capacitance retained after 1000 cycles.

Asymmetric supercapacitors with high energy density based on helical hierarchical porous Na x MnO2 and MoO2.

PubMed

Lu, Xue-Feng; Huang, Zhi-Xiang; Tong, Ye-Xiang; Li, Gao-Ren

2016-01-01

Helical hierarchical porous Na x MnO 2 /CC and MoO 2 /CC, which are assembled from nanosheets and nanoparticles, respectively, are fabricated using a simple electrodeposition method. These unique helical porous structures enable electrodes to have a high capacitance and an outstanding cycling performance. Based on the helical Na x MnO 2 /CC as the positive electrodes and helical MoO 2 /CC as the negative electrodes, high performance Na x MnO 2 /CC//MoO 2 /CC asymmetric supercapacitors (ASCs) are successfully assembled, and they achieve a maximum volume C sp of 2.04 F cm -3 and a maximum energy density of 0.92 mW h cm -3 for the whole device and an excellent cycling stability with 97.22% C sp retention after 6000 cycles.

Graphene oxide-dispersed pristine CNTs support for MnO2 nanorods as high performance supercapacitor electrodes.

PubMed

You, Bo; Li, Na; Zhu, Hongying; Zhu, Xiaolan; Yang, Jun

2013-03-01

A MnO2 -CNT-graphene oxide (MCGO) nanocomposite is fabricated using graphene oxide (GO) as a surfactant to directly disperse pristine carbon nanotubes (CNTs) for the subsequent deposition of MnO2 nanorods. The resulting MCGO nanocomposite is used as a supercapacitor electrode that shows ideal capacitive behavior (i.e., rectangular-shaped cyclic voltammograms), large specific capacitance (4.7 times higher than that of free MnO2 ) even at high mass loading (3.0 mg cm(-2) ), high energy density (30.4-14.2 Wh kg(-1) ), large power density (2.6-50.5 kW kg(-1) ), and still retains approximately 94 % of the initial specific capacitance after 1000 cycles. The advanced capacity, rate capability, and cycling stability may be attributed to the unique architecture, excellent ion wettability of GO with enriched oxygen-containing functional groups, high conductivity of CNTs, and their synergistic effects when combined with the other components. The results suggest that the MnO2 -CNT-GO hybrid nanocomposite architecture is very promising for next generation high-performance energy storage devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrochemical preparation of MnO2 nanobelts through pulse base-electrogeneration and evaluation of their electrochemical performance

NASA Astrophysics Data System (ADS)

Aghazadeh, Mustafa; Maragheh, Mohammad Ghannadi; Ganjali, Mohammad Reza; Norouzi, Parviz; Faridbod, Farnoush

2016-02-01

Cathodic electrodeposition of MnO2 from a nitrate solution, via pulsed base (OH-) electrogeneration was performed for the first time. The deposition experiments were performed in a pulse current mode in typical on-times and off-times (i.e. ton = 1 s and toff = 1 s) with a peak current density of 2 mA cm-2 (Ia = 2 mA cm-2). The structural characterizations conducted by XRD and FTIR techniques revealed that the prepared MnO2 is composed of both α and γ phases. Morphological observation by SEM and TEM showed that the prepared MnO2 is made up of nanobelts with uniform shapes (an average diameter and length of 50 nm and 1 μm, respectively). Further electrochemical measurements by cyclic voltammetry and charge-discharge techniques revealed that the prepared MnO2 nanostructures have excellent capacitive behaviors, like a specific capacitance of 235.5 F g-1 and capacity retention of 91.3% after 1000 cycling at the scan rate of 25 mV s-1.

Matrix composition and community structure analysis of a novel bacterial pyrite leaching community.

PubMed

Ziegler, Sibylle; Ackermann, Sonia; Majzlan, Juraj; Gescher, Johannes

2009-09-01

Here we describe a novel bacterial community that is embedded in a matrix of carbohydrates and bio/geochemical products of pyrite (FeS(2)) oxidation. This community grows in stalactite-like structures--snottites--on the ceiling of an abandoned pyrite mine at pH values of 2.2-2.6. The aqueous phase in the matrix contains 200 mM of sulfate and total iron concentrations of 60 mM. Micro-X-ray diffraction analysis showed that jarosite [(K,Na,H(3)O)Fe(3)(SO(4))(2)(OH)(6)] is the major mineral embedded in the snottites. X-ray absorption near-edge structure experiments revealed three different sulfur species. The major signal can be ascribed to sulfate, and the other two features may correspond to thiols and sulfoxides. Arabinose was detected as the major sugar component in the extracellular polymeric substance. Via restriction fragment length polymorphism analysis, a community was found that mainly consists of iron oxidizing Leptospirillum and Ferrovum species but also of bacteria that could be involved in dissimilatory sulfate and dissimilatory iron reduction. Each snottite can be regarded as a complex, self-contained consortium of bacterial species fuelled by the decomposition of pyrite.

Chemistry of [Et4N][MoIV(SPh)(PPh3)(mnt)2] as an analogue of dissimilatory nitrate reductase with its inactivation on substitution of thiolate by chloride.

PubMed

Majumdar, Amit; Pal, Kuntal; Sarkar, Sabyasachi

2006-04-05

Structural-functional analogue of the reduced site of dissimilatory nitrate reductase is synthesized as [Et4N][MoIV(SPh)(PPh3)(mnt)2].CH2Cl2 (1). PPh3 in 1 is readily dissociated in solution to generate the active site of the reduced site of dissimilatory nitrate reductase. This readily reacts with nitrate. The nitrate reducing system is characterized by substrate saturation kinetics. Oxotransfer to and from substrate has been coupled to produce a catalytic system, NO3- + PPh3 --> NO2- + OPPh3, where NO3- is the substrate for dissimilatory nitrate reductase. The corresponding chloro complex, [Et4N][MoIV(Cl)(PPh3)(mnt)2].CH2Cl2 (2), responds to similar PPh3 dissociation but is unable to react with nitrate, showing the indispensable role of thiolate coordination for such oxotransfer reaction. This investigation provides the initial demonstration of the ligand specificity in a model system similar to single point mutation involving site directed mutagenesis in this class of molybdoenzymes.

Sonochemically synthesized MnO2 nanoparticles as electrode material for supercapacitors.

PubMed

Gnana Sundara Raj, Balasubramaniam; Asiri, Abdullah M; Qusti, Abdullah H; Wu, Jerry J; Anandan, Sambandam

2014-11-01

In this study, manganese oxide (MnO2) nanoparticles were synthesized by sonochemical reduction of KMnO4 using polyethylene glycol (PEG) as a reducing agent as well as structure directing agent under room temperature in short duration of time and characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis. A supercapacitor device constructed using the ultrasonically-synthesized MnO2 nanoparticles showed maximum specific capacitance (SC) of 282Fg(-1) in the presence of 1M Ca(NO3)2 as an electrolyte at a current density of 0.5mAcm(-2) in the potential range from 0.0 to 1.0V and about 78% of specific capacitance was retained even after 1000 cycles indicating its high electrochemical stability. Copyright © 2013 Elsevier B.V. All rights reserved.

Hierarchical MnO2 nanowire/graphene hybrid fibers with excellent electrochemical performance for flexible solid-state supercapacitors

NASA Astrophysics Data System (ADS)

Ma, Wujun; Chen, Shaohua; Yang, Shengyuan; Chen, Wenping; Cheng, Yanhua; Guo, Yiwei; Peng, Shengjie; Ramakrishna, Seeram; Zhu, Meifang

2016-02-01

Towards rapid development of lightweight, flexible, and even wearable electronics, a highly efficient energy-storage device is required for their energy supply management. Graphene fiber-based supercapacitor is considered as one of the promising candidates because of the remarkable mechanical and electrical properties of graphene fibers. However, supercapacitors based on bare graphene fibers generally suffer a low capacitance, which certainly restricts their potentially wide applications. In this work, hierarchically structured MnO2 nanowire/graphene hybrid fibers are fabricated through a simple, scalable wet-spinning method. The hybrid fibers form mesoporous structure with large specific surface area of 139.9 m2 g-1. The mass loading of MnO2 can be as high as 40 wt%. Due to the synergistic effect between MnO2 nanowires and graphene, the main pseudocapacitance of MnO2 and the electric double-layer capacitance of graphene are improved simultaneously. In view of the practical demonstration, a highly flexible solid-state supercapacitor is fabricated by twisting of two MnO2/graphene fibers coated by polyvinyl alcohol/H3PO4 electrolyte. The supercapacitor exhibits a high volumetric capacitance (66.1 F cm-3, normalized by the total volume of two fiber electrodes), excellent cycling stability (96% capacitance retention over 10,000 cycles), high energy and power density (5.8 mWh cm-3 and 0.51 W cm-3, respectively).

Facile Synthesis of Three-Dimensional Sandwiched MnO2@GCs@MnO2 Hybrid Nanostructured Electrode for Electrochemical Capacitors.

PubMed

Jian, Xian; Liu, Shiyu; Gao, Yuqi; Zhang, Wanli; He, Weidong; Mahmood, Asif; M Subramaniyam, Chandrasekar; Wang, Xiaolin; Mahmood, Nasir; Dou, Shi Xue

2017-06-07

Designable control over the morphology and structure of active materials is highly desirable for achieving high-performance devices. Here, we develop a facile microwave-assisted synthesis to decorate MnO 2 nanocrystals on three-dimensional (3D) graphite-like capsules (GCs) to obtain sandwich nanostructures (3D MnO 2 @GCs@MnO 2 ) as electrode materials for electrochemical capacitors (ECs). A templated growth of the 3D GCs was carried out via catalytic chemical vapor deposition and MnO 2 was decorated on the exterior and interior surfaces of the GC walls through microwave irradiation to build an engineered architecture with robust structural and morphological stability. The unique sandwiched architecture has a large interfacial surface area, and allows for rapid electrolyte diffusion through its hollow/open framework and fast electronic motion via the carbon backbone. Furthermore, the tough and rigid nature of GCs provides the necessary structural stability, and the strong synergy between MnO 2 and GCs leads to high electrochemical activity in both neutral (265.1 F/g at 0.5 A/g) and alkaline (390 F/g at 0.5 A/g) electrolytes. The developed hybrid exhibits stable capacitance up to 6000 cycles in 1 M Na 2 SO 4 . The hybrid is a potential candidate for future ECs and the present study opens up an effective avenue to design hybrid materials for various applications.

Flower-, wire-, and sheet-like MnO2-deposited diatomites: Highly efficient absorbents for the removal of Cr(VI).

PubMed

Du, Yucheng; Wang, Liping; Wang, Jinshu; Zheng, Guangwei; Wu, Junshu; Dai, Hongxing

2015-03-01

Flower-, wire-, and sheet-like MnO2-deposited diatomites have been prepared using a hydrothermal method with Mn(Ac)2, KMnO4 and/or MnSO4 as Mn source and diatomite as support. Physical properties of the materials were characterized by means of numerous analytical techniques, and their behaviors in the adsorption of chromium(VI) were evaluated. It is shown that the MnO2-deposited diatomite samples with different morphologies possessed high surface areas and abundant surface hydroxyl groups (especially the wire-like MnO2/diatomite sample). The wire-like MnO2/diatomite sample showed the best performance in the removal of Cr(VI), giving the maximum Cr(VI) adsorption capacity of 101 mg/g. Copyright © 2014. Published by Elsevier B.V.

Photocatalytic oxidation of aromatic amines using MnO2@g ...

EPA Pesticide Factsheets

An efficient and direct oxidation of aromatic amines to aromatic azo-compounds has been achieved using a MnO2@g-C3N4 catalyst under visible light as a source of energy at room temperature Prepared for submission to the journal, Advanced Materials Letters.

A sensitive turn on fluorescent probe for detection of biothiols using MnO2@carbon dots nanocomposites

NASA Astrophysics Data System (ADS)

Garg, Dimple; Mehta, Akansha; Mishra, Amit; Basu, Soumen

2018-03-01

Presently, the combination of carbon quantum dots (CQDs) and metal oxide nanostructures in one frame are being considered for the sensing of purine compounds. In this work, a combined system of CQDs and MnO2 nanostructures was used for the detection of anticancer drugs, 6-Thioguanine (6-TG) and 6-Mercaptopurine (6-MP). The CQDs were synthesized through microwave synthesizer and the MnO2 nanostructures (nanoflowers and nanosheets) were synthesized using facile hydrothermal technique. The CQDs exhibited excellent fluorescence emission at 420 nm when excited at 320 nm wavelength. By combining CQDs and MnO2 nanostructures, quenching of fluorescence was observed which was attributed to fluorescence resonance energy transfer (FRET) mechanism, where CQDs act as electron donor and MnO2 act as acceptor. This fluorescence quenching behaviour disappeared on the addition of 6-TG and 6-MP due to the formation of Mn-S bond. The detection limit for 6-TG (0.015 μM) and 6-MP (0.014 μM) was achieved with the linear range of concentration (0-50 μM) using both MnO2 nanoflowers and nanosheets. Moreover, the as-prepared fluorescence-sensing technique was successfully employed for the detection of bio-thiol group in enapril drug. Thus a facile, cost-effective and benign chemistry approach for biomolecule detection was designed.

Porous honeycomb structures formed from interconnected MnO2 sheets on CNT-coated substrates for flexible all-solid-state supercapacitors

NASA Astrophysics Data System (ADS)

Ko, Wen-Yin; Chen, You-Feng; Lu, Ke-Ming; Lin, Kuan-Jiuh

2016-01-01

The use of lightweight and easily-fabricated MnO2/carbon nanotube (CNT)-based flexible networks as binder-free electrodes and a polyvinyl alcohol/H2SO4 electrolyte for the formation of stretchable solid-state supercapacitors was examined. The active electrodes were fabricated from 3D honeycomb porous MnO2 assembled from cross-walled and interconnected sheet-architectural MnO2 on CNT-based plastic substrates (denoted as honeycomb MnO2/CNT textiles).These substrates were fabricated through a simple two-step procedure involving the coating of multi-walled carbon nanotubes (MWCNTs) onto commercial textiles by a dipping-drying process and subsequent electrodeposition of the interconnected MnO2 sheets onto the MWCNT-coated textile. With such unique MnO2 architectures integrated onto CNT flexible films, good performance was achieved with a specific capacitance of 324 F/g at 0.5 A/g. A maximum energy density of 7.2 Wh/kg and a power density as high as 3.3 kW/kg were exhibited by the honeycomb MnO2/CNT network device, which is comparable to the performance of other carbon-based and metal oxide/carbon-based solid-state supercapacitor devices. Specifically, the long-term cycling stability of this material is excellent, with almost no loss of its initial capacitance and good Coulombic efficiency of 82% after 5000 cycles. These impressive results identify these materials as a promising candidate for use in environmentally friendly, low-cost, and high-performance flexible energy-storage devices.

Porous honeycomb structures formed from interconnected MnO2 sheets on CNT-coated substrates for flexible all-solid-state supercapacitors

PubMed Central

Ko, Wen-Yin; Chen, You-Feng; Lu, Ke-Ming; Lin, Kuan-Jiuh

2016-01-01

The use of lightweight and easily-fabricated MnO2/carbon nanotube (CNT)-based flexible networks as binder-free electrodes and a polyvinyl alcohol/H2SO4 electrolyte for the formation of stretchable solid-state supercapacitors was examined. The active electrodes were fabricated from 3D honeycomb porous MnO2 assembled from cross-walled and interconnected sheet-architectural MnO2 on CNT-based plastic substrates (denoted as honeycomb MnO2/CNT textiles).These substrates were fabricated through a simple two-step procedure involving the coating of multi-walled carbon nanotubes (MWCNTs) onto commercial textiles by a dipping-drying process and subsequent electrodeposition of the interconnected MnO2 sheets onto the MWCNT-coated textile. With such unique MnO2 architectures integrated onto CNT flexible films, good performance was achieved with a specific capacitance of 324 F/g at 0.5 A/g. A maximum energy density of 7.2 Wh/kg and a power density as high as 3.3 kW/kg were exhibited by the honeycomb MnO2/CNT network device, which is comparable to the performance of other carbon-based and metal oxide/carbon-based solid-state supercapacitor devices. Specifically, the long-term cycling stability of this material is excellent, with almost no loss of its initial capacitance and good Coulombic efficiency of 82% after 5000 cycles. These impressive results identify these materials as a promising candidate for use in environmentally friendly, low-cost, and high-performance flexible energy-storage devices. PMID:26726724

High-Performance 2.6 V Aqueous Asymmetric Supercapacitors based on In Situ Formed Na0.5 MnO2 Nanosheet Assembled Nanowall Arrays.

PubMed

Jabeen, Nawishta; Hussain, Ahmad; Xia, Qiuying; Sun, Shuo; Zhu, Junwu; Xia, Hui

2017-08-01

The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na 0.5 MnO 2 nanosheet assembled nanowall arrays are in situ formed on carbon cloth via electrochemical oxidation. It is interesting to find that the electrode potential window for Na 0.5 MnO 2 nanowall arrays can be extended to 0-1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g -1 . The extended potential window for the Na 0.5 MnO 2 electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe 3 O 4 nanorod arrays are synthesized as the anode and can stably work in a negative potential window of -1.3 to 0 V (vs Ag/AgCl). For the first time, a 2.6 V aqueous asymmetric supercapacitor is demonstrated by using Na 0.5 MnO 2 nanowall arrays as the cathode and carbon-coated Fe 3 O 4 nanorod arrays as the anode. In particular, the 2.6 V Na 0.5 MnO 2 //Fe 3 O 4 @C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg -1 as well as excellent rate capability and cycle performance, outperforming previously reported MnO 2 -based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

MnO2-x nanosheets on stainless steel felt as a carbon- and binder-free cathode for non-aqueous lithium-oxygen batteries

NASA Astrophysics Data System (ADS)

Wei, Z. H.; Zhao, T. S.; Zhu, X. B.; Tan, P.

2016-02-01

Manganese dioxide (MnO2) has been recognized as an effective catalyst for the oxygen reduction and oxygen evolution reactions in non-aqueous lithium-oxygen batteries. However, a further improvement in battery performance with the MnO2 catalyst is limited by its low electronic conductivity and catalytic activity, which strongly depend on the morphology and composition. In this work, we develop a carbon- and binder-free MnO2-x nanosheets/stainless steel (SS) cathode via a simple and effective electrodeposition-solvothermal route. The created Mn(III) and oxygen vacancy in MnO2-x nanosheets allows an significant increase in the electronic conductivity and catalytic activity. It is experimentally shown that the use of the present nanostructure MnO2-x/SS cathode in a non-aqueous lithium-oxygen battery results in a rechargeable specific capacity of 7300 mAh g-1 at a current density of 200 mA g-1, which is 39% higher than that with the MnO2/SS cathode. In addition, the specific capacities at 400 mA g-1 and 800 mA g-1 reach 5249 mAh g-1 and 2813 mAh g-1, respectively, which are over 30% higher than that with the MnO2/SS cathode. Furthermore, the discharge/charge cycle test shows no degradation for 120 cycles. All the results show that the present nanostructure MnO2-x/SS cathode is a promising candidate for high-performance lithium-oxygen batteries.

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

NASA Astrophysics Data System (ADS)

Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

2015-03-01

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm-2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm-2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

Surface Reactivity of Li2MnO3: First-Principles and Experimental Study.

PubMed

Quesne-Turin, Ambroise; Flahaut, Delphine; Croguennec, Laurence; Vallverdu, Germain; Allouche, Joachim; Charles-Blin, Youn; Chotard, Jean-Noël; Ménétrier, Michel; Baraille, Isabelle

2017-12-20

This article deals with the surface reactivity of (001)-oriented Li 2 MnO 3 crystals investigated from a multitechnique approach combining material synthesis, X-ray photoemission spectroscopy (XPS), scanning electron microscopy, Auger electron spectroscopy, and first-principles calculations. Li 2 MnO 3 is considered as a model compound suitable to go further in the understanding of the role of tetravalent manganese atoms in the surface reactivity of layered lithium oxides. The knowledge of the surface properties of such materials is essential to understand the mechanisms involved in parasitic phenomena responsible for early aging or poor storage performances of lithium-ion batteries. The surface reactivity was probed through the adsorption of SO 2 gas molecules on large Li 2 MnO 3 crystals to be able to focus the XPS beam on the top of the (001) surface. A chemical mapping and XPS characterization of the material before and after SO 2 adsorption show in particular that the adsorption is homogeneous at the micro- and nanoscale and involves Mn reduction, whereas first-principles calculations on a slab model of the surface allow us to conclude that the most energetically favorable species formed is a sulfate with charge transfer implying reduction of Mn.

Correlating Local Structure with Electrochemical Activity in L i2MnO 3

DOE PAGES

Nanda, Jagjit; Sacci, Robert L.; Veith, Gabriel M.; ...

2015-07-31

Li 2MnO 3 is of interest as one component of the composite lithium-rich oxides, which are under development for high capacity, high voltage cathodes in lithium ion batteries. Despite such practical importance, the mechanism of electrochemical activity in Li 2MnO 3 is contested in the literature, as are the effects of long-term electrochemical cycling. Here, Raman spectroscopy and mapping are used to follow the chemical and structural changes that occur in Li 2MnO 3. Both conventional slurry electrodes and thin films are studied as a function of the state of charge (voltage) and cycle number. Thin films have similar electrochemicalmore » properties as electrodes prepared from slurries, but allow for spectroscopic investigations on uniform samples without carbon additives. Spectral changes correlate well with electrochemical activity and support a mechanism whereby capacity is lost upon extended cycling due to the formation of new manganese oxide phases. Raman mapping of both thin film and slurry electrodes charged to different voltages reveals significant variation in the local structure. Poor conductivity and slow kinetics associated with a two-phase reaction mechanism contribute to the heterogeneity.« less

Mechanochemical Synthesis of Li2MnO3 Shell/LiMO2 (M = Ni, Co, Mn) Core-Structured Nanocomposites for Lithium-Ion Batteries

PubMed Central

Noh, Jae-Kyo; Kim, Soo; Kim, Haesik; Choi, Wonchang; Chang, Wonyoung; Byun, Dongjin; Cho, Byung-Won; Chung, Kyung Yoon

2014-01-01

Core/shell-like nanostructured xLi2MnO3·(1−x)LiMO2 (M = Ni, Co, Mn) composite cathode materials are successfully synthesized through a simple solid-state reaction using a mechanochemical ball-milling process. The LiMO2 core is designed to have a high-content of Ni, which increases the specific capacity. The detrimental surface effects arising from the high Ni-content are countered by the Li2MnO3 shell, which stabilizes the nanoparticles. The electrochemical performances and thermal stabilities of the synthesized nanocomposites are compared with those of bare LiMO2. In particular, the results of time-resolved X-ray diffraction (TR-XRD) analyses of xLi2MnO3·(1−x)LiMO2 nanocomposites as well as their differential scanning calorimetry (DSC) profiles demonstrate that the Li2MnO3 shell is effective in stabilizing the LiMO2 core at high temperatures, making the nanocomposites highly suitable from a safety viewpoint. PMID:24784478

MnO2-Graphene Oxide-PEDOT:PSS Nanocomposite for an Electrochemical Supercapacitor

NASA Astrophysics Data System (ADS)

Patil, Dipali S.; Pawar, Sachin A.; Shin, Jae Cheol; Kim, Hyo Jin

2018-04-01

A ternary nanocomposite with poly (3,4 ethylene dioxythiophene:poly(styrene sulfonate) (PEDOT:PSS)-MnO2 nanowires-graphene oxide (PMn-GO) was synthesized by using simple chemical route. The formation of the nanocomposite was analyzed by using X-ray diffraction and X-ray photoelectron spectroscopy. Field-emission scanning microscopy (FESEM) revealed the formation of MnO2 nanowires and graphene oxide nanosheets. The highest specific capacitance (areal capacitance) of 841 Fg -1 (177 mFcm -2) at 10 mVs -1 and energy density of 0.593 kWhkg -1 at 0.5 mA were observed for PMn-GO, indicating a constructive synergistic effect of PEDOT:PSS, MnO2 nanowires and graphene oxide. The achieved promising electrochemical characteristics showed that this ternary nanocomposite is a good alternative as an electrode material for supercapacitor.

Hierarchically structured MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Sun, Zhipeng; Firdoz, Shaik; Ying-Xuan Yap, Esther; Li, Lan; Lu, Xianmao

2013-05-01

We report a hierarchical Ni@MnO2 structure consisting of MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors. The Ni@MnO2 structure, which was prepared via a facile electrodeposition method, is highly porous and appears like a forest of pine trees grown vertically on a substrate. At a MnO2 mass loading of 0.35 mg cm-2, the Ni@MnO2 electrode demonstrated a specific capacitance of 1125 F g-1 that is close to the theoretical value. In addition, a remarkable high-rate performance (766 F g-1 at a discharge current density of 100 A g-1) was achieved. Electrochemical tests in a two-electrode configuration for the Ni@MnO2 structure with a high MnO2 loading of 3.6 mg cm-2 showed a low equivalent series resistance (ESR) of 1 Ω and a high specific power of 72 kW kg-1. This superior performance can be attributed to the highly porous and hierarchical structure of Ni@MnO2 that favors rapid diffusion of an electrolyte, highly conductive pathway for electron transport, and efficient material utilization.We report a hierarchical Ni@MnO2 structure consisting of MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors. The Ni@MnO2 structure, which was prepared via a facile electrodeposition method, is highly porous and appears like a forest of pine trees grown vertically on a substrate. At a MnO2 mass loading of 0.35 mg cm-2, the Ni@MnO2 electrode demonstrated a specific capacitance of 1125 F g-1 that is close to the theoretical value. In addition, a remarkable high-rate performance (766 F g-1 at a discharge current density of 100 A g-1) was achieved. Electrochemical tests in a two-electrode configuration for the Ni@MnO2 structure with a high MnO2 loading of 3.6 mg cm-2 showed a low equivalent series resistance (ESR) of 1 Ω and a high specific power of 72 kW kg-1. This superior performance can be attributed to the highly porous and hierarchical structure of Ni@MnO2 that favors rapid diffusion of an electrolyte, highly

MnO2/CNT supported Pt and PtRu nanocatalysts for direct methanol fuel cells.

PubMed

Zhou, Chunmei; Wang, Hongjuan; Peng, Feng; Liang, Jiahua; Yu, Hao; Yang, Jian

2009-07-07

Pt/MnO2/carbon nanotube (CNT) and PtRu/MnO2/CNT nanocomposites were synthesized by successively loading hydrous MnO2 and Pt (or PtRu alloy) nanoparticles on CNTs and were used as anodic catalysts for direct methanol fuel cells (DMFCs). The existence of MnO2 on the surface of CNTs effectively increases the proton conductivity of the catalyst, which then could remarkably improve the performance of the catalyst in methanol electro-oxidation. As a result, Pt/MnO2/CNTs show higher electrochemical active surface area and better methanol electro-oxidation activity, compared with Pt/CNTs. As PtRu alloy nanoparticles were deposited on the surface of MnO2/CNTs instead of Pt, the PtRu/MnO2/CNT catalyst shows not only excellent electro-oxidation activity to methanol with forward anodic peak current density of 901 A/gPt but also good CO oxidation ability with lower preadsorbed CO oxidation onset potential (0.33 V vs Ag/AgCl) and peak potential (0.49 V vs Ag/AgCl) at room temperature.

DNA-assisted assembly of carbon nanotubes and MnO2 nanospheres as electrodes for high-performance asymmetric supercapacitors.

PubMed

Guo, Chun Xian; Chitre, Amey Anil; Lu, Xianmao

2014-03-14

A DNA-assisted assembly approach is developed to fabricate a capacitor-type electrode material, DNA-functionalized carbon nanotubes (CNTs@DNA), and a battery-type electrode material, DNA@CNTs-bridged MnO2 spheres (CNTs@DNA-MnO2), for asymmetric supercapacitors. An energy density of 11.6 W h kg(-1) is achieved at a power density of 185.5 W kg(-1) with a high MnO2 mass loading of 4.2 mg cm(-2). It is found that DNA assembly plays a critical role in the enhanced supercapacitor performance. This is because while DNA molecules functionalize carbon nanotubes (CNTs) via π-π stacking, their hydrophilic sugar-phosphate backbones also promote the dispersion of CNTs. The resultant CNTs@DNA chains can link multiple MnO2 spheres to form a networked architecture that facilitates charge transfer and effective MnO2 utilization. The improved performance of the asymmetric supercapacitors indicates that DNA-assisted assembly offers a promising approach to the fabrication of high-performance energy storage devices.

Single-layer MnO2 nanosheets for sensitive and selective detection of glutathione by a colorimetric method

NASA Astrophysics Data System (ADS)

Di, Weihua; Zhang, Xiang; Qin, Weiping

2017-04-01

The rapid, sensitive and selective detection of glutathione (GSH) is of great importance in the biological systems. In this work, a template-free and one-step method was used to synthesize the single-layer MnO2 nanosheets via a redox reaction. The resulting product was characterized by XRD, TEM, FTIR, XPS and UV-vis absorption. The addition of GSH results in the change of solution color depth owing to the occurrence of a redox reaction between MnO2 and GSH, enabling colorimetric detection of GSH. At a pH of 3.6, the proposed sensor gives a linear calibration over a GSH concentration range of 10-100 μM, with a rapid response of less than 2 min and a low detection limit of 0.5 μM. The relative standard deviation for seven repeated determinations of GSH is lower than 5.6%. Furthermore, the chemical response of the synthesized MnO2 nanosheets toward GSH is selective. Owing to the advantages with good water solubility, rapid response, high sensitivity, good biocompatibility and operation simplicity, this two-dimensional MnO2-based sensing material might be potential for detecting GSH in biological applications.

Enhanced tolerance to stretch-induced performance degradation of stretchable MnO2-based supercapacitors.

PubMed

Huang, Yan; Huang, Yang; Meng, Wenjun; Zhu, Minshen; Xue, Hongtao; Lee, Chun-Sing; Zhi, Chunyi

2015-02-04

The performance of many stretchable electronics, such as energy storage devices and strain sensors, is highly limited by the structural breakdown arising from the stretch imposed. In this article, we focus on a detailed study on materials matching between functional materials and their conductive substrate, as well as enhancement of the tolerance to stretch-induced performance degradation of stretchable supercapacitors, which are essential for the design of a stretchable device. It is revealed that, being widely utilized as the electrode material of the stretchable supercapacitor, metal oxides such as MnO2 nanosheets have serious strain-induced performance degradation due to their rigid structure. In comparison, with conducting polymers like a polypyrrole (PPy) film as the electrochemically active material, the performance of stretchable supercapacitors can be well preserved under strain. Therefore, a smart design is to combine PPy with MnO2 nanosheets to achieve enhanced tolerance to strain-induced performance degradation of MnO2-based supercapacitors, which is realized by fabricating an electrode of PPy-penetrated MnO2 nanosheets. The composite electrodes exhibit a remarkable enhanced tolerance to strain-induced performance degradation with well-preserved performance over 93% under strain. The detailed morphology and electrochemical impedance variations are investigated for the mechanism analyses. Our work presents a systematic investigation on the selection and matching of electrode materials for stretchable supercapacitors to achieve high performance and great tolerance to strain, which may guide the selection of functional materials and their substrate materials for the next-generation of stretchable electronics.

A successive ionic layer adsorption and reaction (SILAR) method to fabricate a layer-by-layer (LbL) MnO2-reduced graphene oxide assembly for supercapacitor application

NASA Astrophysics Data System (ADS)

Jana, Milan; Saha, Sanjit; Samanta, Pranab; Murmu, Naresh Chandra; Kim, Nam Hoon; Kuila, Tapas; Lee, Joong Hee

2017-02-01

A facile, cost effective and additive-free successive ionic layer adsorption and reaction (SILAR) technique is demonstrated to develop layer-by-layer (LbL) assembly of reduced graphene oxide (RGO) and MnO2 (MnO2-RGOSILAR) on a stainless steel current collector, for designing light-weight and small size supercapacitor electrode. The transmission electron microscopy and field emission scanning electron microscopy images shows uniform distribution of RGO and MnO2 in the MnO2-RGOSILAR. The LbL (MnO2-RGOSILAR) demonstrates improved physical and electrochemical properties over the hydrothermally prepared MnO2-RGO (MnO2-RGOHydro). The electrochemical environment of MnO2-RGOSILAR is explained by constant phase element in the high frequency region, and a Warburg element in the low frequency region in the Z-View fitted Nyquist plot. The equivalent circuit of the MnO2-RGOHydro, displays the co-existence of EDL and constant phase element, indicating inhomogeneous distribution of MnO2 and RGO by the hydrothermal technique. An asymmetric supercapacitor device is designed with MnO2-RGOSILAR as positive electrode, and thermally reduced GO (TRGO) as negative electrode. The designed cell exhibits high energy density of ∼88 Wh kg-1, elevated power density of ∼23,200 W kg-1, and ∼79% retention in capacitance after 10,000 charge-discharge cycles.

Hydrothermal Synthesis of Nanostructured MnO2 and Gamma Radiation Effects on Rechargeable Lithium Battery Performance.

PubMed

Seo, Sang-Ei; Kang, Yun Ok; Jung, Sung-Hee; Choi, Seong-Ho

2015-09-01

Nanostructured manganese dioxide (MnO2) was synthesized by the hydrothermal method under various experimental conditions such as reaction time and concentration in order to obtain nanostructure material with different morphologies, and it was found that the morphology of the MnO2 obtained had a nanoparticle-like structure, urchin-like structure, or nanorod-like structure depending on the experimental conditions. Among the as-prepared MnO2 samples, the highest surface area was seen for the urchin-like structure, and this was irradiated by γ-rays with a total radiation dose of 30 kGy at a rate 1.0 x 10(4) Gy/h in order to determine the effect of γ-irradiation on battery performance. There was a decrease in battery performance in terms of capacity and stability for irradiated samples during 100 cycles.

3D hierarchical architecture based on 1D TiO2 nanorod and 2D MnO2 nanoflake for high performance supercapacitor electrode

NASA Astrophysics Data System (ADS)

Thakur, S.; Maiti, S.; Acharya, A.; Paul, T.; Besra, N.; Sarkar, S.; Chattopadhyay, K. K.

2018-04-01

Possibility of integration of manifold functionalities coupled with novel interface phenomenon generation in geometrically intricate hierarchical nanoform has made them greatly pertinent from both research and technological point of view. Here, oxide based hybrid has been realized by integrating 1D TiO2 nanorod with 2D MnO2 nanoflake via low temperature chemical route. Meticulous tunability over the hierarchical morphology was achieved by subtle variation of reaction parameter which in turn created difference in MnO2 growth over TiO2. Morphological features of the samples were examined by FESEM and TEM. Hybrid samples exhibited high electrochemical performance than pristine TiO2 nanorods. Registered electrochemical performance from TiO2-MnO2 hybrid was found to be ˜1024F/g at a current density of 0.66A/g which is ˜100 fold than TiO2 at same current density. Such enhanced performance is accounted from higher surface area and electrical conductivity of the hybrid.

Carbon supported MnO2-CoFe2O4 with enhanced electrocatalytic activity for oxygen reduction and oxygen evolution

NASA Astrophysics Data System (ADS)

Wang, Ying; Liu, Qing; Hu, Tianjun; Zhang, Limin; Deng, Youquan

2017-05-01

The catalyst MnO2-CoFe2O4/C was firstly synthesized via a two-step process and applied as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media. The composite exhibits better bifunctional activity than CoFe2O4/C and MnO2/C. Moreover, superior durability and high methanol tolerance in alkaline media outperforms the commercial Pt/C electrocatalyst, which signifying its excellent potential for applications in metal-air batteries and alkaline fuel cells.

Few-layered MnO2/SWCNT hybrid in-plane supercapacitor with high energy density

NASA Astrophysics Data System (ADS)

Dutta, Shibsankar; Pal, Shreyasi; De, Sukanta

2018-05-01

In this present work we have synthesized few layered MnO2 nanosheets by mixed solvent exfoliation process for the application as electrode material of in-plane supercapacitor. The Structure and surface morphology of the as prepared samples are characterized by Raman, Transmission electron microscopy and Scanning electron microscopy. The patterns of the hybrids were directly fabricated by (50: 50 wt %) mixture of MnO2 and SWCNT dispersions with the help of a customized mask, and directly transferred onto a flexible PET substrate. Remarkably, the prepared in-plane supercapacitors deliver high energy density of 2.62mWh/cm2. Furthermore, our supercapacitors shows exceptional flexibility and stable performance under bending conditions

Design and synthesis of hierarchical MnO2 nanospheres/carbon nanotubes/conducting polymer ternary composite for high performance electrochemical electrodes.

PubMed

Hou, Ye; Cheng, Yingwen; Hobson, Tyler; Liu, Jie

2010-07-14

For efficient use of metal oxides, such as MnO(2) and RuO(2), in pseudocapacitors and other electrochemical applications, the poor conductivity of the metal oxide is a major problem. To tackle the problem, we have designed a ternary nanocomposite film composed of metal oxide (MnO(2)), carbon nanotube (CNT), and conducting polymer (CP). Each component in the MnO(2)/CNT/CP film provides unique and critical function to achieve optimized electrochemical properties. The electrochemical performance of the film is evaluated by cyclic voltammetry, and constant-current charge/discharge cycling techniques. Specific capacitance (SC) of the ternary composite electrode can reach 427 F/g. Even at high mass loading and high concentration of MnO(2) (60%), the film still showed SC value as high as 200 F/g. The electrode also exhibited excellent charge/discharge rate and good cycling stability, retaining over 99% of its initial charge after 1000 cycles. The results demonstrated that MnO(2) is effectively utilized with assistance of other components (fFWNTs and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) in the electrode. Such ternary composite is very promising for the next generation high performance electrochemical supercapacitors.

Design and synthesis of hierarchical mesoporous WO3-MnO2 composite nanostructures on carbon cloth for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Shinde, Pragati A.; Lokhande, Vaibhav C.; Patil, Amar M.; Ji, Taeksoo; Lokhande, Chandrakant D.

2017-12-01

To enhance the energy density and power performance of supercapacitors, the rational design and synthesis of active electrode materials with hierarchical mesoporous structure is highly desired. In the present work, fabrication of high-performance hierarchical mesoporous WO3-MnO2 composite nanostructures on carbon cloth substrate via a facile hydrothermal method is reported. By varying the content of MnO2 in the composite, different WO3-MnO2 composite thin films are obtained. The formation of composite is confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. The Brunauer-Emmett-Teller (BET) analysis reveals maximum specific surface area of 153 m2 g-1. The optimized WO3-MnO2 composite electrode demonstrates remarkable electrochemical performance with high specific capacitance of 657 F g-1 at a scan rate of 5 mV s-1 and superior longterm cycling stability (92% capacity retention over 2000 CV cycles). Furthermore, symmetric flexible solid-state supercapacitor based on WO3-MnO2 electrodes has been fabricated. The device exhibits good electrochemical performance with maximum specific capacitance of 78 F g-1 at a scan rate of 5 mV s-1 and specific energy of 10.8 Wh kg-1 at a specific power of 0.65 kW kg-1. The improved electrochemical performance could be ascribed to the unique combination of multivalence WO3 and MnO2 nanostructures and synergistic effect between them

3D hierarchical MnO2 nanorod/welded Ag-nanowire-network composites for high-performance supercapacitor electrodes.

PubMed

Qiao, Zhensong; Yang, Xiaopeng; Yang, Shuhua; Zhang, Liqiang; Cao, Bingqiang

2016-06-28

3D MnO2 nanorod/welded Ag-nanowire-network supercapacitor electrodes were prepared. Welding treatment of the Ag nanowire-network leads to low resistance and long lifetime. Galvanostatic charge/discharge (GCD) induces an ever-lasting morphology changing from flower-like to honeycomb-like for MnO2, which manifests as increasing specific capacitance to 663.4 F g(-1) after 7000 GCD cycles.

Oxygen evolution from BF3/MnO4-.

PubMed

Yiu, Shek-Man; Man, Wai-Lun; Wang, Xin; Lam, William W Y; Ng, Siu-Mui; Kwong, Hoi-Ki; Lau, Kai-Chung; Lau, Tai-Chu

2011-04-14

MnO(4)(-) is activated by BF(3) to undergo intramolecular coupling of two oxo ligands to generate O(2). DFT calculations suggest that there should be a spin intercrossing between the singlet and triplet potential energy surfaces on going from the active intermediate [MnO(2)(OBF(3))(2)](-) to the O···O coupling transition state.

Carbon Quantum Dot-Induced MnO2 Nanowire Formation and Construction of a Binder-Free Flexible Membrane with Excellent Superhydrophilicity and Enhanced Supercapacitor Performance.

PubMed

Lv, Haipeng; Gao, Xiujiao; Xu, Qunjie; Liu, Haimei; Wang, Yong-Gang; Xia, Yongyao

2017-11-22

Manganese oxides (MnO 2 ) are regarded as typical and promising electrode materials for supercapacitors. However, the practical electrochemical performance of MnO 2 is far from its theoretical value. Nowadays, numerous efforts are being devoted to the design and preparation of nanostructured MnO 2 with the aim of improving its electrochemical properties. In this work, ultralong MnO 2 nanowires were fabricated in a process induced by carbon quantum dots (CQDs); subsequently, a binder-free flexible electrode membrane was easily obtained by vacuum filtration of the MnO 2 nanowires. The effects of the CQDs not only induced the formation of one-dimensional nanostructured MnO 2 , but also significantly improved the wettability between electrode and electrolyte. In other words, the MnO 2 membrane demonstrated a superhydrophilic character in aqueous solution, indicating the sufficient and abundant contact probability between electrode and electrolyte. The binder-free flexible MnO 2 electrode exhibited a preeminent specific capacitance of 340 F g -1 at 1 A g -1 ; even when the current density reached 20 A g -1 , it still maintained 260 F g -1 (76% retention rate compared to that at 1 A g -1 ). Moreover, it also showed good cycling stability with 80.1% capacity retention over 10 000 cycles at 1 A g -1 . Furthermore, an asymmetric supercapacitor was constructed using the MnO 2 membrane and active carbon as the positive and negative electrodes, respectively, which exhibited a high energy density of 33.6 Wh kg -1 at 1.0 kW kg -1 , and a high power density of 10 kW kg -1 at 12.5 Wh kg -1 .

Microwave assisted synthesis of graphene oxide - MnO2 nanocomposites for electrochemical supercapacitors

NASA Astrophysics Data System (ADS)

Vimuna, V. M.; Athira, A. R.; Xavier, T. S.

2018-05-01

Grapheneoxide-MnO2 nanocomposite was successfully synthesized through the self-limiting deposition of nano scale MnO2 on the surface of graphene oxide under microwave- irradiation in a water- isopropyl alcohol system. The structural and morphological properties of as synthesized samples have been studied. These nanostructured graphene oxide-MnO2 (GMC) hybrid materials are used for investigation of electrochemical behaviours. It was found that the electrochemical performance of as prepared nanocomposite could be enhanced by chemical interaction between GO and MnO2. Cyclic voltammetry is employed to assess the properties of these nanocomposites for use in supercapacitors. The specific capacitance of the synthesized sample corresponding to scan rate of 20mV/s is calculated to be 280 Fg-1. Furthermore, we emphasize the fabrication challenges and future perspectives of such materials for energy storage.

MnO2 ultrathin films deposited by means of magnetron sputtering: Relationships between process conditions, structural properties and performance in transparent supercapacitors

NASA Astrophysics Data System (ADS)

Borysiewicz, Michał A.; Wzorek, Marek; Myśliwiec, Marcin; Kaczmarski, Jakub; Ekielski, Marek

2016-12-01

This study focuses on the relationships between the process parameters during magnetron sputter deposition of MnO2 and the resulting film properties. Three MnO2 phases were identified - γ, β and λ and the dependence of MnO2 phase presence on the oxygen content in the sputtering atmosphere was found. Selected MnO2 phases were subsequently applied as ultrathin coatings on top of nanostructured ZnO electrodes for transparent supercapacitors with LiCl-based gel electrolyte. The films containing λ-MnO2 exhibited both the highest optical transparency of 62% at 550 nm as well as the highest specific capacitance in the supercapacitor structure, equal to 73.1 μF/cm2. Initially lower, the capacitance was elevated by charge-discharge conditioning.

Fe3O4 and MnO2 assembled on honeycomb briquette cinders (HBC) for arsenic removal from aqueous solutions.

PubMed

Zhu, Jin; Baig, Shams Ali; Sheng, Tiantian; Lou, Zimo; Wang, Zhuoxing; Xu, Xinhua

2015-04-09

In this study, a novel composite adsorbent (HBC-Fe3O4-MnO2) was synthesized by combining honeycomb briquette cinders (HBC) with Fe3O4 and MnO2 through a co-precipitation process. The purpose was to make the best use of the oxidative property of MnO2 and the adsorptive ability of magnetic Fe3O4 for enhanced As(III) and As(V) removal from aqueous solutions. Experimental results showed that the adsorption capacity of As(III) was observed to be much higher than As(V). The maximum adsorption capacity (2.16 mg/g) was achieved for As(III) by using HBC-Fe3O4-MnO2 (3:2) as compared to HBC-Fe3O4-MnO2 (2:1) and HBC-Fe3O4-MnO2 (1:1). The experimental data of As(V) adsorption fitted well with the Langmuir isotherm model, whereas As(III) data was described perfectly by Freundlich model. The pseudo-second-order kinetic model was fitted well for the entire adsorption process of As(III) and As(V) suggesting that the adsorption is a rate-controlling step. Aqueous solution pH was found to greatly affect the adsorption behavior. Furthermore, co-ions including HCO3(-) and PO4(3-) exhibited greater influence on arsenic removal efficiency, whereas Cl(-), NO3(-), SO4(2-) were found to have negligible effects on arsenic removal. Five consecutive adsorption-regeneration cycles confirmed that the adsorbent could be reusable for successive arsenic treatment and can be used in real treatment applications. Copyright © 2015 Elsevier B.V. All rights reserved.

MnO2 nanowires-decorated carbon fiber cloth as electrodes for aqueous asymmetric supercapacitor

NASA Astrophysics Data System (ADS)

Hong, Congcong; Wang, Xing; Yu, Houlin; Wu, Huaping; Wang, Jianshan; Liu, Aiping

Manganese dioxide nanowires (MnO2 NWs) anchored on carbon fiber cloth (CFC) were fabricated through a simple hydrothermal reaction and used as integrated electrodes for supercapacitor. The morphology-dependent electrochemical performance of MnO2 NWs was confirmed, yielding good capacitance performance with a high specific capacitance of 3.88Fṡcm‑2 at a charge-discharge current density of 5mAṡcm‑2 and excellent stability of 91.5% capacitance retention after 3000 cycles. Moreover, the composite electrodes were used to fabricate supercapacitors, which showed a high specific capacitance of 194mFṡcm‑2 at a charge-discharge current density of 2mAṡcm‑2 and high energy density of 0.108mWhṡcm‑2 at power density of 2mWṡcm‑2, foreboding its potential application for high-performance supercapacitor.

Resistance switching mechanism of La0.8Sr0.2MnO3-δ thin films

NASA Astrophysics Data System (ADS)

Luo, X. D.; Gao, R. L.; Fu, C. L.; Cai, W.; Chen, G.; Deng, X. L.; Zhang, H. R.; Sun, J. R.

2016-02-01

Effects of oxygen vacancies on the electrical transport properties of oxygen stoichiometric La0.8Sr0.2MnO3 and oxygen-deficient La0.8Sr0.2MnO3-δ films have been investigated. The result presents that the oxygen-deficient films annealed in vacuum show obvious increase of resistance and lattice parameter. With the sweeping voltage or temperature increasing, the resistance exhibits obvious bipolar switching effect, no forming process was needed. Oxygen deficiency in the annealed film leads to the formation of a structural disorder in the Mn-O-Mn conduction channel due to the accumulation of oxygen vacancies under high external electric field or temperatures and hence is believed to be responsible for the bipolar resistance switching effect and the enhanced resistivity compared with oxygen stoichiometric La0.8Sr0.2MnO3 film. These results may be important for practical applications in photoelectric or storage devices and point to a useful direction for other oxidizing materials.

Live-Cell MicroRNA Imaging through MnO2 Nanosheet-Mediated DD-A Hybridization Chain Reaction.

PubMed

Ou, Min; Huang, Jin; Yang, Xiaohai; He, Xiaoxiao; Quan, Ke; Yang, Yanjing; Xie, Nuli; Li, Jing; Wang, Kemin

2018-01-18

Innovative techniques to visualize native microRNAs (miRNAs) in live cells can dramatically impact current research on the roles of miRNA in biology and medicine. Here, we report a novel approach for live-cell miRNA imaging using a biodegradable MnO 2 nanosheet-mediated DD-A FRET hybridization chain reaction (HCR). The MnO 2 nanosheets can adsorb DNA hairpin probes and deliver them into live cells. After entering cells, the MnO 2 nanosheets are degraded by cellular GSH. Then, the target miR-21 triggers cascaded assembly of the liberated hairpin probes into long dsDNA polymers, which brings each two FAMs (donor) and one TAMRA (acceptor) into close proximity to generate significantly enhanced DD-A FRET signals, which was discovered and proven by our previous report. We think the developed approach can serve as an excellent intracellular miRNAs detection tool, which promises the potential for biological and disease studies. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fluorescence turn-on detection of alkaline phosphatase activity based on controlled release of PEI-capped Cu nanoclusters from MnO2 nanosheets.

PubMed

Zhang, Yunyi; Li, Yongxin; Zhang, Cuiyun; Zhang, Qingfeng; Huang, Xinan; Yang, Meiding; Shahzad, Sohail Anjum; Lo, Kenneth Kam-Wing; Yu, Cong; Jiang, Shichun

2017-08-01

A fluorescence turn-on assay for alkaline phosphatase (ALP) activity is developed through the controlled release of polyethyleneimine-capped copper nanoclusters (PEI-capped CuNCs) from the MnO 2 nanosheets. In an aqueous solution, the positively charged PEI-capped CuNCs could be adsorbed onto the surface of the negatively charged MnO 2 nanosheets. Such adsorption through favorable electrostatic interactions could efficiently quench the nanocluster fluorescence emission via resonance energy transfer from the PEI-capped CuNCs to the MnO 2 nanosheets. 2-Phospho-L-ascorbic acid (AAP) could be hydrolyzed to L-ascorbic acid (AA) in the presence of ALP. AA could reduce MnO 2 into Mn 2+ and trigger the disintegration of the MnO 2 nanosheets. As a result, the CuNCs were released and the quenched fluorescence was recovered efficiently. The detection strategy is simple, inexpensive, sensitive, selective, with low toxicity, and has better biocompatibility. The newly fabricated biosensor for ALP activity will potentially make it a robust candidate for numerous biological and biomedical applications.

La2/3Sr1/3MnO3-La0.1Bi0.9MnO3 heterostructures for spin filtering

NASA Astrophysics Data System (ADS)

Gajek, M.; Bibes, M.; Varela, M.; Fontcuberta, J.; Herranz, G.; Fusil, S.; Bouzehouane, K.; Barthélémy, A.; Fert, A.

2006-04-01

We have grown heterostructures associating half-metallic La2/3Sr1/3MnO3 (LSMO) bottom electrodes and ferromagnetic La0.1Bi0.9MnO3 (LBMO) tunnel barriers. The layers in the heterostructures have good structural properties and top LBMO films (4 nm thick) have a very low roughness when deposited onto LSMO/SrTiO3(1.6 nm) templates. The LBMO films show an insulating behavior and a ferromagnetic character that are both preserved down to very low thicknesses. They are thus suitable for being used as tunnel barriers. Spin-dependent transport measurements performed on tunnel junctions defined from LSMO/SrTiO3/LBMO/Au samples show a magnetoresistance of up to ~90% at low temperature and bias. This evidences a spin-filtering effect by the LBMO layer, with a spin-filtering efficiency of ~35%.

Prevention of PVDF ultrafiltration membrane fouling by coating MnO2 nanoparticles with ozonation

PubMed Central

Yu, Wenzheng; Brown, Matthew; Graham, Nigel. J. D.

2016-01-01

Pre-treatment is normally required to reduce or control the fouling of ultrafiltration (UF) membranes in drinking water treatment process. Current pre-treatment methods, such as coagulation, are only partially effective to prevent long-term fouling. Since biological activities are a major contributor to accumulated fouling, the application of an oxidation/disinfection step can be an effective complement to coagulation. In this study, a novel pre-treatment method has been evaluated at laboratory scale consisting of the addition of low dose ozone into the UF membrane tank after coagulation and the use of a hollow-fibre membrane coated with/without MnO2 nanoparticles over a test period of 70 days. The results showed that there was minimal fouling of the MnO2 coated membrane (0.5 kPa for 70 days), while the uncoated membrane experienced both reversible and irreversible fouling. The difference was attributed to the greatly reduced presence of bacteria and organic matter because of the catalytic decomposition of ozone to hydroxyl radicals and increase of the hydrophilicity of the membrane surface. In particular, the MnO2 coated membrane had a much thinner cake layer, with significantly less polysaccharides and proteins, and much less accumulated organic matter within the membrane pores. PMID:27436142

Prevention of PVDF ultrafiltration membrane fouling by coating MnO2 nanoparticles with ozonation

NASA Astrophysics Data System (ADS)

Yu, Wenzheng; Brown, Matthew; Graham, Nigel. J. D.

2016-07-01

Pre-treatment is normally required to reduce or control the fouling of ultrafiltration (UF) membranes in drinking water treatment process. Current pre-treatment methods, such as coagulation, are only partially effective to prevent long-term fouling. Since biological activities are a major contributor to accumulated fouling, the application of an oxidation/disinfection step can be an effective complement to coagulation. In this study, a novel pre-treatment method has been evaluated at laboratory scale consisting of the addition of low dose ozone into the UF membrane tank after coagulation and the use of a hollow-fibre membrane coated with/without MnO2 nanoparticles over a test period of 70 days. The results showed that there was minimal fouling of the MnO2 coated membrane (0.5 kPa for 70 days), while the uncoated membrane experienced both reversible and irreversible fouling. The difference was attributed to the greatly reduced presence of bacteria and organic matter because of the catalytic decomposition of ozone to hydroxyl radicals and increase of the hydrophilicity of the membrane surface. In particular, the MnO2 coated membrane had a much thinner cake layer, with significantly less polysaccharides and proteins, and much less accumulated organic matter within the membrane pores.

Suppressing the Coffee-Ring Effect in Semitransparent MnO2 Film for a High-Performance Solar-Powered Energy Storage Window.

PubMed

Jin, Huanyu; Qian, Jiasheng; Zhou, Limin; Yuan, Jikang; Huang, Haitao; Wang, Yu; Tang, Wing Man; Chan, Helen Lai Wa

2016-04-13

We introduce a simple and effective method to deposit a highly uniform and semitransparent MnO2 film without coffee-ring effect (CRE) by adding ethanol into MnO2 ink for transparent capacitive energy storage devices. By carefully controlling the amount of ethanol added in the MnO2 droplet, we could significantly reduce the CRE and thus improve the film uniformity. The electrochemical properties of supercapacitor (SC) devices using semitransparent MnO2 film electrodes with or without CRE were measured and compared. The SC device without CRE shows a superior capacitance, high rate capability, and lower contact resistance. The CRE-free device could achieve a considerable volumetric capacitance of 112.2 F cm(-3), resulting in a high volumetric energy density and power density of 10 mWh cm(-3) and 8.6 W cm(-3), respectively. For practical consideration, both flexible SC and large-area rigid SC devices were fabricated to demonstrate their potential for flexible transparent electronic application and capacitive energy-storage window application. Moreover, a solar-powered energy storage window which consists of a commercial solar cell and our studied semitransparent MnO2-film-based SCs was assembled. These SCs could be charged by the solar cell and light up a light emitting diode (LED), demonstrating their potential for self-powered systems and energy-efficient buildings.

Rational design of octahedron and nanowire CeO2@MnO2 core-shell heterostructures with outstanding rate capability for asymmetric supercapacitors.

PubMed

Zhu, Shi Jin; Jia, Jia Qi; Wang, Tian; Zhao, Dong; Yang, Jian; Dong, Fan; Shang, Zheng Guo; Zhang, Yu Xin

2015-10-14

Two kinds of novel CeO2@MnO2 nanostructures have been synthesized via a self-assembly strategy. The as-prepared CeO2 nanowire@MnO2 nanostructures exhibited unprecedented pseudocapacitance performance (255 F g(-1)) with outstanding rate capability. A new mechanism based on the synergistic effect between CeO2 and MnO2 was proposed to interpret this phenomenon. When assembled as an asymmetric supercapacitor, an energy density of 27.5 W h kg(-1) with a maximum power density of 1.6 kW kg(-1) was achieved for CeO2 nanowire@MnO2 nanostructures.

Morphology-controlled synthesis and novel microwave electromagnetic properties of hollow urchin-like chain Fe-doped MnO 2 under 10 T high magnetic field

NASA Astrophysics Data System (ADS)

Yuping, Duan; Jia, Zhang; Hui, Jing; Shunhua, Liu

2011-05-01

Fe-doped MnO 2 with a hollow sea urchin-like ball chain shape was first synthesized under a high magnetic field of 10 T. The formation mechanism was investigated and discussed in detail. The synthesized samples were characterized by XRD, SEM, TEM, EMPA, and vector network analysis. By doping MnO 2 with Fe, the relative complex permittivity of MnO 2 and its corresponding loss tangent clearly decreases, but its relative complex permeability and its corresponding loss tangent markedly increases. Moreover, the theoretically calculated values of reflection loss show that with increasing the Fe content, the as-prepared Fe-doped MnO 2 exhibits good microwave absorption capability.

The Influence of Carbonaceous Matrices and Electrocatalytic MnO2 Nanopowders on Lithium-Air Battery Performances

PubMed Central

Minguzzi, Alessandro; Longoni, Gianluca; Cappelletti, Giuseppe; Pargoletti, Eleonora; Di Bari, Chiara; Locatelli, Cristina; Marelli, Marcello; Rondinini, Sandra; Vertova, Alberto

2016-01-01

Here, we report new gas diffusion electrodes (GDEs) prepared by mixing two different pore size carbonaceous matrices and pure and silver-doped manganese dioxide nanopowders, used as electrode supports and electrocatalytic materials, respectively. MnO2 nanoparticles are finely characterized in terms of structural (X-ray powder diffraction (XRPD), energy dispersive X-ray (EDX)), morphological (SEM, high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM)/TEM), surface (Brunauer Emmet Teller (BET)-Barrett Joyner Halenda (BJH) method) and electrochemical properties. Two mesoporous carbons, showing diverse surface areas and pore volume distributions, have been employed. The GDE performances are evaluated by chronopotentiometric measurements to highlight the effects induced by the adopted materials. The best combination, hollow core mesoporous shell carbon (HCMSC) with 1.0% Ag-doped hydrothermal MnO2 (M_hydro_1.0%Ag) allows reaching very high specific capacity close to  1400 mAh·g−1. Considerably high charge retention through cycles is also observed, due to the presence of silver as a dopant for the electrocatalytic MnO2 nanoparticles. PMID:28344267

MnO2-GO double-shelled sulfur (S@MnO2@GO) as a cathode for Li-S batteries with improved rate capability and cyclic performance

NASA Astrophysics Data System (ADS)

Huang, Xingkang; Shi, Keying; Yang, Joseph; Mao, George; Chen, Junhong

2017-07-01

Sulfur cathodes have attracted much attention recently because of their high energy density and power density. However, sulfur possesses very poor electrical conductivity, and lithium polysulfides, resulting from the lithiation of sulfur, are prone to dissolving into electrolytes, which leads to the loss of active materials and poor cyclic performance of the sulfur cathodes. Here we report an MnO2-graphene oxide (GO) double-shelled sulfur (S@MnO2@GO) with improved rate capability and cyclic performance, in which we propose a new reaction using sulfur-reducing KMnO4 to produce MnO2 that covers the surface of the excess sulfur in situ. The resulting MnO2 with honeycomb-like morphology provides excellent voids for storing polysulfides. The outermost GO was assembled to block the open pores of MnO2, thereby minimizing the opportunity for polysulfides to leach into the electrolytes. The GO significantly improved the electrical conductivity of the sulfur cathode, and the S@MnO2@GO exhibited excellent rate capability and long cycle life.

Porous graphitic carbon microtubes derived from willow catkins as a substrate of MnO2 for supercapacitors

NASA Astrophysics Data System (ADS)

Zhang, Xiaohua; Zhang, Kang; Li, Hengxiang; Cao, Qing; Jin, Li'e.; Li, Ping

2017-03-01

Biomass is receiving considerable attention because of its significant advantages as a sustainable and renewable material. Willow catkins, which have a single-walled microtubular structure are used as both a template and a precursor for synthesizing porous graphitic carbon microtubes (PGCMT) induced by the simultaneous activation-graphitization of K4Fe(CN)6. In addition to providing low-resistant pathways and short ion diffusion channels, as-obtained PGCMT with tubular structure also serves as an ideal platform for anchoring MnO2. The PGCMT/MnO2 composite electrode obtained by MnO2 electrodeposition expressed excellent electrochemical performance, including a significantly enhanced specific capacitance (550.8 F g-1 for the mass of MnO2 at a current density of 2 A g-1), a high capacitance retention of 61.8% even at a high current density of 50 A g-1, and an excellent cycling stability of 89.6% capability retention after 5000 cycles. These findings offer a simple and environmentally friendly strategy for preparing advanced energy materials by utilizing the unique structure of biomass waste from nature.

Comparison on surface properties and desulfurization of MnO2 and pyrolusite blended activated carbon by steam activation.

PubMed

Zhang, Guochen; Zhao, Xin; Ning, Ping; Yang, Danni; Jiang, Xia; Jiang, Wenju

2018-04-18

In this study, MnO 2 and pyrolusite were used as the catalysts to prepare modified activated carbon, i.e., AC-Mn and AC-P, respectively, from coals by blending method and steam activation. The BET results indicated that the AC-P had higher surface areas and micropore volumes than the AC-Mn with the same blending ratio. The relative contents of basic functional groups (i.e. C = O, π-π*) on AC-P were slightly lower than those on AC-Mn, while both contained the same main metal species, i.e. MnO. The desulfurization results showed that with 3 wt% of blending ratio, AC-Mn3 and AC-P3 had higher sulfur capacities at 220 and 205 mg/g, respectively, which were much higher than blank one (149.6 mg/g). Moreover, the AC-P had relatively higher sulfur capacity than the AC-Mn with the same contents of Mn, which might be attributed to the existence of other metals in pyrolusite. After desulfurization process, MnO were gradually transferred into MnSO 4 , and the relative contents of basic functional groups decreased evidently for both AC-Mn3 and AC-P3. The results demonstrated that pyrolusite could be one good alternative of MnO 2 to prepare modified activated carbon for desulfurization. Implication statement MnO 2 and pyrolusite were used as the additives to prepare the modified activated carbon from coals by blending method and steam activation, i.e., AC-Mn and AC-P, respectively. The AC-P had higher surface areas and micropore volumes than the AC-Mn with the same blending ratio. The AC-Mn and AC-P had higher sulfur capacities than blank one. Moreover, the AC-P had relatively higher sulfur capacity than the AC-Mn with the same contents of Mn. The results demonstrated that pyrolusite could be one good alternative of MnO 2 to prepare modified activated carbon for desulfurization.

Facile synthesis of hierarchical mesoporous weirds-like morphological MnO2 thin films on carbon cloth for high performance supercapacitor application.

PubMed

Shinde, Pragati A; Lokhande, Vaibhav C; Ji, Taeksoo; Lokhande, Chandrakant D

2017-07-15

The mesoporous nanostructured metal oxides have a lot of capabilities to upsurge the energy storing capacity of the supercapacitor. In present work, different nanostructured morphologies of MnO 2 have been successfully fabricated on flexible carbon cloth by simple but capable hydrothermal method at different deposition temperatures. The deposition temperature has strong influence on reaction kinetics, which subsequently alters the morphology and electrochemical performance. Among different nanostructured MnO 2 thin films, the mesoporous weirds composed thin film obtained at temperature of 453K exhibits excellent physical and electrochemical features for supercapacitor application. The weirds composed MnO 2 thin film exhibits specific surface area of 109m 2 g -1 , high specific capacitance of 595Fg -1 with areal capacitance of 4.16Fcm -2 at a scan rate of 5mVs -1 and high specific energy of 56.32Whkg -1 . In addition to this, MnO 2 weirds attain capacity retention of 87 % over 2000 CV cycles, representing better cycling stability. The enhanced electrochemical performance could be ascribed to direct growth of highly porous MnO 2 weirds on carbon cloth which provide more pathways for easy diffusion of electrolyte into the interior of electroactive material. The as-fabricated electrode with improved performance could be ascribed as a potential electrode material for energy storage devices. Copyright © 2017 Elsevier Inc. All rights reserved.

Constraints on the utility of MnO2 cartridge method for the extraction of radionuclides: A case study using 234Th

USGS Publications Warehouse

Baskaran, M.; Swarzenski, P.W.; Biddanda, B.A.

2009-01-01

[1] Large volume (102-103 L) seawater samples are routinely processed to investigate the partitioning of particle reactive radionuclides and Ra between solution and size-fractionated suspended particulate matter. One of the most frequently used methods to preconcentrate these nuclides from such large volumes involves extraction onto three filter cartridges (a prefilter for particulate species and two MnO2-coated filters for dissolved species) connected in series. This method assumes that the extraction efficiency is uniform for both MnO2-coated cartridges, that no dissolved species are removed by the prefilter, and that any adsorbed radionuclides are not desorbed from the MnO2-coated cartridges during filtration. In this study, we utilized 234Th-spiked coastal seawater and deionized water to address the removal of dissolved Th onto prefilters and MnO2-coated filter cartridges. Experimental results provide the first data that indicate (1) a small fraction of dissolved Th (<6%) can be removed by the prefilter cartridge; (2) a small fraction of dissolved Th (<5%) retained by the MnO2 surface can also be desorbed, which undermines the assumption of uniform extraction efficiency for Th; and (3) the absolute and relative extraction efficiencies can vary widely. These experiments provide insight on the variability of the extraction efficiency of MnO 2-coated filter cartridges by comparing the relative and absolute efficiencies and recommend the use of a constant efficiency on the combined activity from two filter cartridges connected in series for future studies of dissolved 234Th and other radionuclides in natural waters using sequential filtration/extraction methods. ?? 2009 by the American Geophysical Union.

3D hierarchical assembly of ultrathin MnO2 nanoflakes on silicon nanowires for high performance micro-supercapacitors in Li- doped ionic liquid

PubMed Central

Dubal, Deepak P.; Aradilla, David; Bidan, Gérard; Gentile, Pascal; Schubert, Thomas J.S.; Wimberg, Jan; Sadki, Saïd; Gomez-Romero, Pedro

2015-01-01

Building of hierarchical core-shell hetero-structures is currently the subject of intensive research in the electrochemical field owing to its potential for making improved electrodes for high-performance micro-supercapacitors. Here we report a novel architecture design of hierarchical MnO2@silicon nanowires (MnO2@SiNWs) hetero-structures directly supported onto silicon wafer coupled with Li-ion doped 1-Methyl-1-propylpyrrolidinium bis(trifluromethylsulfonyl)imide (PMPyrrBTA) ionic liquids as electrolyte for micro-supercapacitors. A unique 3D mesoporous MnO2@SiNWs in Li-ion doped IL electrolyte can be cycled reversibly across a voltage of 2.2 V and exhibits a high areal capacitance of 13 mFcm−2. The high conductivity of the SiNWs arrays combined with the large surface area of ultrathin MnO2 nanoflakes are responsible for the remarkable performance of these MnO2@SiNWs hetero-structures which exhibit high energy density and excellent cycling stability. This combination of hybrid electrode and hybrid electrolyte opens up a novel avenue to design electrode materials for high-performance micro-supercapacitors. PMID:25985388

Effect of dissimilatory Fe(III) reducers on bio-reduction and nickel-cobalt recovery from Sukinda chromite-overburden.

PubMed

Esther, Jacintha; Panda, Sandeep; Behera, Sunil K; Sukla, Lala B; Pradhan, Nilotpala; Mishra, Barada K

2013-10-01

The effect of an adapted dissimilatory iron reducing bacterial consortium (DIRB) towards bio-reduction of Sukinda chromite overburden (COB) with enhanced recovery of nickel and cobalt is being reported for the first time. The remarkable ability of DIRB to utilize Fe(III) as terminal electron acceptor reducing it to Fe(II) proved beneficial for treatment of COB as compared to previous reports for nickel leaching. XRD studies showed goethite as the major iron-bearing phase in COB. Under facultative anaerobic conditions, goethite was reduced to hematite and magnetite with the exposure of nickel oxide. FESEM studies showed DIRB to be associated with COB through biofilm formation with secondary mineral precipitates of magnetite deposited as tiny globular clusters on the extra polymeric substances. The morphological and mineralogical changes in COB, post DIRB application, yielded a maximum of 68.5% nickel and 80.98% cobalt in 10 days using 8M H2SO4. Copyright © 2013 Elsevier Ltd. All rights reserved.

MnO2 nanosheet mediated "DD-A" FRET binary probes for sensitive detection of intracellular mRNA.

PubMed

Ou, Min; Huang, Jin; Yang, Xiaohai; Quan, Ke; Yang, Yanjing; Xie, Nuli; Wang, Kemin

2017-01-01

The donor donor-acceptor (DD-A) FRET model has proven to have a higher FRET efficiency than donor-acceptor acceptor (D-AA), donor-acceptor (D-A), and donor donor-acceptor acceptor (DD-AA) FRET models. The in-tube and in-cell experiments clearly demonstrate that the "DD-A" FRET binary probes can indeed increase the FRET efficiency and provide higher imaging contrast, which is about one order of magnitude higher than the ordinary "D-A" model. Furthermore, MnO 2 nanosheets were employed to deliver these probes into living cells for intracellular TK1 mRNA detection because they can adsorb ssDNA probes, penetrate across the cell membrane and be reduced to Mn 2+ ions by intracellular GSH. The results indicated that the MnO 2 nanosheet mediated "DD-A" FRET binary probes are capable of sensitive and selective sensing gene expression and chemical-stimuli changes in gene expression levels in cancer cells. We believe that the MnO 2 nanosheet mediated "DD-A" FRET binary probes have the potential as a simple but powerful tool for basic research and clinical diagnosis.

Nitrogen-doped hollow porous carbon nanospheres coated with MnO2 nanosheets as excellent sulfur hosts for Li-S batteries

NASA Astrophysics Data System (ADS)

Zhang, Xiaolong; Yang, He; Guo, Junling; Zhao, Shupeng; Gong, Shoutao; Du, Xinyu; Zhang, Fengxiang

2017-11-01

In this work, nitrogen-doped hollow porous carbon nanospheres coated with MnO2 nanosheets (NHPC@MnO2) were prepared as a novel sulfur host for the cathode of lithium-sulfur battery. N-doping of carbon and deposition of the inherently polar MnO2 promote chemical binding of the host with sulfur and its reduction products, known as polysulfides. Meanwhile, proper N-doping can improve the electron conductivity of carbon, and the nanosheet structure may help to guarantee facile electron- and lithium-ion transport through MnO2. Attributed to these advantages, the NHPC@MnO2/S cathode with a high sulfur content (70 wt% and 2.6 mg cm-2) exhibited an excellent cycle stability: its capacity retention was 93% within 100 cycles at 0.5 C. It also displayed a good rate capability: discharge capacities being ˜1130 mAh g-1 at 0.2 C, ˜1000 mAh g-1 at 0.5 C, ˜820 mAh g-1 at 1 C, and ˜630 mAh g-1 at 2 C. Our work demonstrates the synergistic effect of MnO2 nanostructure and N-doped carbon nanospheres for enhanced performance of lithium-sulfur battery cathodes.

In Situ Growth of MnO2 Nanosheets on N-Doped Carbon Nanotubes Derived from Polypyrrole Tubes for Supercapacitors.

PubMed

Ou, Xu; Li, Qi; Xu, Dan; Guo, Jiangna; Yan, Feng

2018-03-02

Nitrogen-doped porous carbon nanotubes@MnO 2 (N-CNTs@MnO 2 ) nanocomposites are prepared through the in situ growth of MnO 2 nanosheets on N-CNTs derived from polypyrrole nanotubes (PNTs). Benefiting from the synergistic effects between N-CNTs (high conductivity and N doping level) and MnO 2 nanosheets (high theoretical capacity), the as-prepared N-CNTs@MnO 2 -800 nanocomposites show a specific capacitance of 219 F g -1 at a current density of 1.0 A g -1 , which is higher than that of pure MnO 2 nanosheets (128 F g -1 ) and PNTs (42 F g -1 ) in 0.5 m Na 2 SO 4 solution. Meanwhile, the capacitance retention of 86.8 % (after 1000 cycles at 10 A g -1 ) indicates an excellent electrochemical performance of N-CNTs@MnO 2 prepared in this work. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Facile synthesis of hierarchical Co3O4@MnO2 core-shell arrays on Ni foam for asymmetric supercapacitors

NASA Astrophysics Data System (ADS)

Huang, Ming; Zhang, Yuxin; Li, Fei; Zhang, Lili; Wen, Zhiyu; Liu, Qing

2014-04-01

Hierarchical Co3O4@MnO2 core-shell arrays on Ni foam have been fabricated by a facile hydrothermal approach and further investigated as the electrode for high-performance supercapacitors. Owing to the high conductivity of the well-defined mesoporous Co3O4 nanowire arrays in combination with the large surface area provided by the ultrathin MnO2 nanosheets, the unique designed Co3O4@MnO2 core-shell arrays on Ni foam have exhibited a high specific capacitance (560 F g-1 at a current density of 0.2 A g-1), good rate capability, and excellent cycling stability (95% capacitance retention after 5000 cycles). An asymmetric supercapacitor with Co3O4@MnO2 core-shell nanostructure as the positive electrode and activated microwave exfoliated graphite oxide activated graphene (MEGO) as the negative electrode yielded an energy density of 17.7 Wh kg-1 and a maximum power density of 158 kW kg-1. The rational design of the unique core-shell array architectures demonstrated in this work provides a new and facile approach to fabricate high-performance electrode for supercapacitors.

Construction of hierarchical FeCo2O4@MnO2 core-shell nanostructures on carbon fibers for high-performance asymmetric supercapacitor.

PubMed

Zhu, Fangfang; Liu, Yu; Yan, Ming; Shi, Weidong

2018-02-15

In this work, the novel hierarchical FeCo 2 O 4 @MnO 2 core-shell nanosheet arrays have been synthesized by a facile hydrothermal method, which are grown directly on a flexible carbon fiber (CF) as an integrated electrode for supercapacitors. Scanning electron microscopy and high-resolution transmission electron microscopy measurements illustrate that MnO 2 nanoflakes uniformly wrap around the surface of two-dimensional FeCo 2 O 4 nanosheets. The electrode exhibits high areal capacitance of 4.8Fcm -2 at a current density of 1mAcm -2 . Moreover, an asymmetric FeCo 2 O 4 @MnO 2 //active carbon (AC) cell is successfully fabricated. The asymmetric supercapacitor (ASC) displays high energy density/power density (22.68Whkg -1 at 406.01Wkg -1 and 7.06Whkg -1 at 1802.5Wkg -1 ), as well as excellent cycling stability with 90.1% of the initial capacitance after 5000 continuous cycles. Moreover, two ASCs connected in series can light a LED. These performances demonstrate great potential of the designed ASC in the field of energy storage due to their remarkable electrochemical properties. Copyright © 2017. Published by Elsevier Inc.

In-situ growth of MnO2 crystals under nanopore-constraint in carbon nanofibers and their electrochemical performance

PubMed Central

Le, TrungHieu; Yang, Ying; Yu, Liu; Huang, Zheng-hong; Kang, Feiyu

2016-01-01

Growing MnO2 nanocrystals in the bulk of porous carbon nanofibers is conducted in a KMnO4 aqueous solution aimed to enhance the electrochemical performance of MnO2. The rate of redox reaction between KMnO4 and carbon was controlled by the concentration of KMnO4 in a neutral solution. The MnO2 nanoparticles grow along with (211) crystal faces when the redox reaction happens on the surface of fibers under 1D constraint, while the nanoparticles grow along with (200) crystal faces when the redox reaction happens in the bulk of fibers under 3D constraint. The composite, where MnO2 nanoparticles are formed in the bulk under a constraint, yields an electrode material for supercapacitors showing good electron transport, rapid ion penetration, fast and reversible Faradaic reaction, and excellent rate performance. The capacitance of the composite electrode could be 1282 F g−1 under a current density of 0.2 A g−1 in 1 M Na2SO4 electrolyte. A symmetric supercapacitor delivers energy density of 36 Wh kg−1 with power density of 39 W kg−1, and can maintain 7.5 Wh kg−1 at 10.3 kW kg−1. It exhibits an excellent electrochemical cycling stability with 101% initial capacitance and 95% columbic efficiency even after 1000 cycles of charge/discharge. PMID:27869184

Nanowire Na0.35MnO2 from a hydrothermal method as a cathode material for aqueous asymmetric supercapacitors

NASA Astrophysics Data System (ADS)

Zhang, B. H.; Liu, Y.; Chang, Z.; Yang, Y. Q.; Wen, Z. B.; Wu, Y. P.; Holze, R.

2014-05-01

Nanowire Na0.35MnO2 was prepared by a simple and low energy consumption hydrothermal method; its electrochemical performance as a cathode material for aqueous asymmetric supercapacitors in Na2SO4 solution was investigated. Due to the nanowire structure its capacitance (157 F g-1) is much higher than that of the rod-like Na0.95MnO2 (92 F g-1) from solid phase reaction although its sodium content is lower. When it is assembled into an asymmetric aqueous supercapacitor using activated carbon as the counter electrode and aqueous 0.5 mol L-1 Na2SO4 electrolyte solution, the nanowire Na0.35MnO2 shows an energy density of 42.6 Wh kg-1 at a power density of 129.8 W kg-1 based on the total weight of the two electrode material, higher than those for the rod-like Na0.95MnO2, with an energy density of 27.3 Wh kg-1 at a power density of 74.8 W kg-1, and that of LiMn2O4. The new material presents excellent cycling behavior even when dissolved oxygen is not removed from the electrolyte solution. The results hold great promise for practical applications of this cathode material since sodium is much cheaper than lithium and its natural resources are rich.

Tailoring nanostructured MnO2 as anodes for lithium ion batteries with high reversible capacity and initial Coulombic efficiency

NASA Astrophysics Data System (ADS)

Zhang, Lifeng; Song, Jiajia; Liu, Yi; Yuan, Xiaoyan; Guo, Shouwu

2018-03-01

Developing high energy storage lithium ion batteries (LIBs) using manganese oxides as anodes is an attractive challenge due to their high theoretical capacity and abundant resources. However, the manganese oxides anodes still suffer from the low initial Coulombic efficiency and poor rate performance. Herein, we demonstrate that nano-sized morphological engineering is a facile and effective strategy to improve the electrochemical performance of the manganese dioxide (MnO2) for LIBs. The tailored MnO2 nanoparticles (NPs) exhibit high reversible capacity (1095 mAh g-1 at 100 mA g-1), high initial Coulombic efficiency (94.5%) and good rate capability (464 mAh g-1 at 2000 mA g-1). The enhanced electrochemical performance of MnO2 NPs can be attributed to the presences of numerous electrochemically active sites and interspaces among the NPs.

CuO, MnO2 and Fe2O3 doped biomass ash as silica source for glass production in Thailand

NASA Astrophysics Data System (ADS)

Srisittipokakun, N.; Ruangtaweep, Y.; Rachniyom, W.; Boonin, K.; Kaewkhao, J.

In this research, glass productions from rice husk ash (RHA) and the effect of BaO, CuO, MnO2 and Fe2O3 on physical and optical properties were investigated. All properties were compared with glass made from SiO2 using same preparations. The results show that a higher density and refractive index of BaO, CuO, MnO2 and Fe2O3 doped in RHA glasses were obtained, compared with SiO2 glasses. The optical spectra show no significant difference between both glasses. The color of CuO glasses show blue from the absorption band near 800 nm (2B1g → 2B2g) due to Cu2+ ion in octahedral coordination with a strong tetragonal distortion. The color of MnO2 glasses shows brown from broad band absorption at around 500 nm. This absorption band is assigned to a single allowed 5Eg → 5T2g transition which arises from the Mn3+ ions (3d4 configuration) in octahedral symmetry. The yellow color derives from F2O3 glass due to the homogeneous distribution of Fe3+ (460 nm) and Fe2+ (1050 nm) ions in the glass matrices. Glass production from RHA is possible and is a new option for recycling waste from biomass power plant systems and air pollution reduction.

Sulfur Isotope Effects of Dissimilatory Sulfite Reductase

PubMed Central

Leavitt, William D.; Bradley, Alexander S.; Santos, André A.; Pereira, Inês A. C.; Johnston, David T.

2015-01-01

The precise interpretation of environmental sulfur isotope records requires a quantitative understanding of the biochemical controls on sulfur isotope fractionation by the principle isotope-fractionating process within the S cycle, microbial sulfate reduction (MSR). Here we provide the only direct observation of the major (34S/32S) and minor (33S/32S, 36S/32S) sulfur isotope fractionations imparted by a central enzyme in the energy metabolism of sulfate reducers, dissimilatory sulfite reductase (DsrAB). Results from in vitro sulfite reduction experiments allow us to calculate the in vitro DsrAB isotope effect in 34S/32S (hereafter, 34εDsrAB) to be 15.3 ± 2‰, 2σ. The accompanying minor isotope effect in 33S, described as 33λDsrAB, is calculated to be 0.5150 ± 0.0012, 2σ. These observations facilitate a rigorous evaluation of the isotopic fractionation associated with the dissimilatory MSR pathway, as well as of the environmental variables that govern the overall magnitude of fractionation by natural communities of sulfate reducers. The isotope effect induced by DsrAB upon sulfite reduction is a factor of 0.3–0.6 times prior indirect estimates, which have ranged from 25 to 53‰ in 34εDsrAB. The minor isotope fractionation observed from DsrAB is consistent with a kinetic or equilibrium effect. Our in vitro constraints on the magnitude of 34εDsrAB is similar to the median value of experimental observations compiled from all known published work, where 34εr−p = 16.1‰ (r–p indicates reactant vs. product, n = 648). This value closely matches those of MSR operating at high sulfate reduction rates in both laboratory chemostat experiments (34εSO4−H2S =  17.3 ± 1.5‰, 2σ) and in modern marine sediments (34εSO4−H2S =  17.3 ± 3.8‰). Targeting the direct isotopic consequences of a specific enzymatic processes is a fundamental step toward a biochemical foundation for reinterpreting the biogeochemical and geobiological sulfur isotope records in

Multiangular Rod-Shaped Na0.44MnO2 as Cathode Materials with High Rate and Long Life for Sodium-Ion Batteries.

PubMed

Liu, Qiannan; Hu, Zhe; Chen, Mingzhe; Gu, Qinfen; Dou, Yuhai; Sun, Ziqi; Chou, Shulei; Dou, Shi Xue

2017-02-01

The tunnel-structured Na 0.44 MnO 2 is considered as a promising cathode material for sodium-ion batteries because of its unique three-dimensional crystal structure. Multiangular rod-shaped Na 0.44 MnO 2 have been first synthesized via a reverse microemulsion method and investigated as high-rate and long-life cathode materials for Na-ion batteries. The microstructure and composition of prepared Na 0.44 MnO 2 is highly related to the sintering temperature. This structure with suitable size increases the contact area between the material and the electrolyte and guarantees fast sodium-ion diffusion. The rods prepared at 850 °C maintain specific capacity of 72.8 mA h g -1 and capacity retention of 99.6% after 2000 cycles at a high current density of 1000 mA g -1 . The as-designed multiangular Na 0.44 MnO 2 provides new insight into the development of tunnel-type electrode materials and their application in rechargeable sodium-ion batteries.

RuO 2 nanoparticles supported on MnO 2 nanorods as high efficient bifunctional electrocatalyst of lithium-oxygen battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Yue-Feng; Chen, Yuan; Xu, Gui-Liang

RuO2 nanoparticles supported on MnO2 nanorods (denoted as np-RuO2/nr-MnO2) were synthesized via a two-step hydrothermal reaction. SEM and TEM images both illustrated that RuO2 nanoparticles are well dispersed on the surface of MnO2 nanorods in the as-prepared np-RuO2/nr-MnO2 material. Electrochemical results demonstrated that the np-RuO2/nr-MnO2 as oxygen cathode of Li-O-2 batteries could maintain a reversible capacity of 500 mA h g(-1) within 75 cycles at a rate of 50 mA g(-1), and a higher capacity of 4000 mA h g(-1) within 20 cycles at a rate as high as 200 mA g(-1). Moreover, the cell with the np-RuO2/nr-MnO2 catalyst presentedmore » much lower voltage polarization (about 0.58 V at a rate of 50 mA g(-1)) than that measured with only MnO2 nanorods during charge/discharge processes. The catalytic property of the np-RuO2/nr-MnO2 and MnO2 nanorods were further compared by conducting studies of using rotating disk electrode (RDE), chronoamperommetry and linear sweep voltammetry. The results illustrated that the np-RuO2/nr-MnO2 exhibited excellent bifunctional electrocatalytic activities towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Furthermore, in-situ high-energy X-ray diffraction was employed to trace evolution of species on the np-RuO2/nr-MnO2 cathode during the discharge processes. In-situ XRD patterns demonstrated the formation process of the discharge products that consisted of mainly Li2O2. Ex-situ SEM images were recorded to investigate the morphology and decomposition of the sphere-like Li2O2, which could be observed clearly after discharge process, while are decomposed almost after charge process. The excellent electrochemical performances of the np-RuO2/nr-MnO2 as cathode of Li-O-2 battery could be contributed to the excellent bifunctional electrocatalytic activities for both the ORR and OER, and to the one-dimensional structure which would benefit the diffusion of oxygen and the storage of Li2O2 in the discharge

Ultrathin MnO2 nanoflakes deposited on carbon nanotube networks for symmetrical supercapacitors with enhanced performance

NASA Astrophysics Data System (ADS)

Sun, Peng; Yi, Huan; Peng, Tianquan; Jing, Yuting; Wang, Ruijing; Wang, Huanwen; Wang, Xuefeng

2017-02-01

Manganese dioxide is a promising electrode material for electrochemical supercapacitors, but its poor electronic conductivity (10-5∼10-6 S cm-1) limits the fast charge/discharge rate for practical applications. In the present work, we use the chemical vapor deposition (CVD) method to grow highly conductive carbon nanotube (CNT) networks on flexible Ni mesh, on which MnO2 nanoflake layers are deposited by a simple solution method, forming a hierarchical core-shell structure. Under the optimized mass loading, the as-fabricated MnO2 nanoflake@CNTs/Ni mesh electrode exhibits a high specific capacitance of 1072 F g-1 at 1 A g-1 in three-electrode configuration. Due to advantageous features of these core-shell electrodes (e.g., high conductivity, direct current path, structure stability), the as-assembled symmetric supercapacitor (SSC) based on MnO2@CNTs/Ni mesh has a wide working voltage (2.0 V) in 1 M Na2SO4 aqueous electrolyte. Finally an impressive energy density of 94.4 Wh kg-1 at 1000 W kg-1 and a high power density of 30.2 kW kg-1 at 33.6 Wh kg-1 have been achieved for the as-assembled SSC, which exhibits a great potential as a low-cost, high energy density and attractive wearable energy storage device.

Bacterial trajectories tracked with time-lapse video-microscopy reveal the impact of manganese biomineralization on bacterial sedimentation.

NASA Astrophysics Data System (ADS)

Kerboas, Camille; Pena, Jasquelin; De Anna, Pietro

2017-04-01

In aquatic and subsurface environments, sedimentation may influence bacterial transport. Microorganisms that carry out biomineralization reactions may exhibit distinct transport properties from non-biomineralizing organisms due an apparent increase in density caused by biomineral production. For several decades, the biomineralization of manganese (Mn) has been recognized to be a major environmental process, whereby Mn oxide (MnO2(s)) minerals participate in a plethora of biogeochemical processes including contaminant adsorption, organic matter oxidation. Typically, manganese biomineralization proceeds through the enzymatic oxidation of aqueous Mn2+ to Mn4+ and precipitation of MnO2(s) in a biofilm matrix outside the bacterial cell. Here, we present a study of the impact of biomineralization on the sedimentation properties of bacteria at small scales (over mm distances) under hydrostatic conditions. We hypothesize that bacteria will sediment faster when biomineralization is active due to encrustation of the organisms by mineral particles. To test this hypothesis, we tracked the vertical notion of individual bacteria (Pseudomonas putida GB-1) using time-lapse video-microscopy. We compared the sedimentation velocity of bacteria in the case where significant biomineralization had occurred, as inferred from bulk measurements of solid phase Mn, with the sinking velocity of bacteria grown without Mn. We calibrated the proposed method by comparing velocity measurements of sinking polystyrene micro-sphere of known density and size with Stokes law, obtaining results that were accurate within 1% of the theoretical value (29.4 nm/s). We also measured a diffusion coefficient of 7x10-13 m2/s for the particles. Following this approach, we measured the sedimentation velocity of P. putida with and without MnO2(s). Our results show that biomineralization leads to faster sedimentation of the bacteria. In natural environments, biomineralization reactions may increase the sinking

Ammonification in Bacillus subtilis Utilizing Dissimilatory Nitrite Reductase Is Dependent on resDE

PubMed Central

Hoffmann, Tamara; Frankenberg, Nicole; Marino, Marco; Jahn, Dieter

1998-01-01

During anaerobic nitrate respiration Bacillus subtilis reduces nitrate via nitrite to ammonia. No denitrification products were observed. B. subtilis wild-type cells and a nitrate reductase mutant grew anaerobically with nitrite as an electron acceptor. Oxygen-sensitive dissimilatory nitrite reductase activity was demonstrated in cell extracts prepared from both strains with benzyl viologen as an electron donor and nitrite as an electron acceptor. The anaerobic expression of the discovered nitrite reductase activity was dependent on the regulatory system encoded by resDE. Mutation of the gene encoding the regulatory Fnr had no negative effect on dissimilatory nitrite reductase formation. PMID:9422613

Dissimilatory nitrate reduction by Aspergillus terreus isolated from the seasonal oxygen minimum zone in the Arabian Sea

PubMed Central

2014-01-01

Background A wealth of microbial eukaryotes is adapted to life in oxygen-deficient marine environments. Evidence is accumulating that some of these eukaryotes survive anoxia by employing dissimilatory nitrate reduction, a strategy that otherwise is widespread in prokaryotes. Here, we report on the anaerobic nitrate metabolism of the fungus Aspergillus terreus (isolate An-4) that was obtained from sediment in the seasonal oxygen minimum zone in the Arabian Sea, a globally important site of oceanic nitrogen loss and nitrous oxide emission. Results Axenic incubations of An-4 in the presence and absence of oxygen and nitrate revealed that this fungal isolate is capable of dissimilatory nitrate reduction to ammonium under anoxic conditions. A 15N-labeling experiment proved that An-4 produced and excreted ammonium through nitrate reduction at a rate of up to 175 nmol 15NH4+ g-1 protein h-1. The products of dissimilatory nitrate reduction were ammonium (83%), nitrous oxide (15.5%), and nitrite (1.5%), while dinitrogen production was not observed. The process led to substantial cellular ATP production and biomass growth and also occurred when ammonium was added to suppress nitrate assimilation, stressing the dissimilatory nature of nitrate reduction. Interestingly, An-4 used intracellular nitrate stores (up to 6–8 μmol NO3- g-1 protein) for dissimilatory nitrate reduction. Conclusions Our findings expand the short list of microbial eukaryotes that store nitrate intracellularly and carry out dissimilatory nitrate reduction when oxygen is absent. In the currently spreading oxygen-deficient zones in the ocean, an as yet unexplored diversity of fungi may recycle nitrate to ammonium and nitrite, the substrates of the major nitrogen loss process anaerobic ammonium oxidation, and the potent greenhouse gas nitrous oxide. PMID:24517718

Dissimilatory nitrate reduction by Aspergillus terreus isolated from the seasonal oxygen minimum zone in the Arabian Sea.

PubMed

Stief, Peter; Fuchs-Ocklenburg, Silvia; Kamp, Anja; Manohar, Cathrine-Sumathi; Houbraken, Jos; Boekhout, Teun; de Beer, Dirk; Stoeck, Thorsten

2014-02-11

A wealth of microbial eukaryotes is adapted to life in oxygen-deficient marine environments. Evidence is accumulating that some of these eukaryotes survive anoxia by employing dissimilatory nitrate reduction, a strategy that otherwise is widespread in prokaryotes. Here, we report on the anaerobic nitrate metabolism of the fungus Aspergillus terreus (isolate An-4) that was obtained from sediment in the seasonal oxygen minimum zone in the Arabian Sea, a globally important site of oceanic nitrogen loss and nitrous oxide emission. Axenic incubations of An-4 in the presence and absence of oxygen and nitrate revealed that this fungal isolate is capable of dissimilatory nitrate reduction to ammonium under anoxic conditions. A ¹⁵N-labeling experiment proved that An-4 produced and excreted ammonium through nitrate reduction at a rate of up to 175 nmol ¹⁵NH₄⁺ g⁻¹ protein h⁻¹. The products of dissimilatory nitrate reduction were ammonium (83%), nitrous oxide (15.5%), and nitrite (1.5%), while dinitrogen production was not observed. The process led to substantial cellular ATP production and biomass growth and also occurred when ammonium was added to suppress nitrate assimilation, stressing the dissimilatory nature of nitrate reduction. Interestingly, An-4 used intracellular nitrate stores (up to 6-8 μmol NO₃⁻ g⁻¹ protein) for dissimilatory nitrate reduction. Our findings expand the short list of microbial eukaryotes that store nitrate intracellularly and carry out dissimilatory nitrate reduction when oxygen is absent. In the currently spreading oxygen-deficient zones in the ocean, an as yet unexplored diversity of fungi may recycle nitrate to ammonium and nitrite, the substrates of the major nitrogen loss process anaerobic ammonium oxidation, and the potent greenhouse gas nitrous oxide.

Influence of Ce Doping on Structural and Transport Properties of Ca1- x Ce x MnO3 ( x=0.2) Manganite

NASA Astrophysics Data System (ADS)

Varshney, Dinesh; Mansuri, Irfan

2011-01-01

We have investigated structural, electric, magnetic and thermal transport properties of electron doped Ca1- x Ce x MnO3 ( x=0.2) manganites. The Cerium substitution for Ca2+causes electron doping into insulating CaMnO3 without e g electron. At room temperature the polycrystalline Ca0.8Ce0.2MnO3 is in the crystallographic orthorhombic structure, with Pnma space group symmetry from the refinement of x-ray powder diffraction patterns. The electrical resistivity data infers that Ca0.8Ce0.2MnO3 manganite is in the semiconducting phase. A smooth linear behavior of log plot values is obtained and is well fitted with adiabatic small polaron conduction model. Nearest-neighbor hopping of a small polaron leads to a mobility with a thermally activated form. The negative values of thermopower infer electron as carriers in Ca0.8Ce0.2MnO3. From susceptibility measurements the Ce doped CaMnO3 shows a transition from antiferromagnetic (AFM) to paramagnetic (PM) phase.

Interactive effects of MnO2, organic matter and pH on abiotic formation of N2O from hydroxylamine in artificial soil mixtures.

PubMed

Liu, Shurong; Berns, Anne E; Vereecken, Harry; Wu, Di; Brüggemann, Nicolas

2017-02-01

Abiotic conversion of the reactive nitrification intermediate hydroxylamine (NH 2 OH) to nitrous oxide (N 2 O) is a possible mechanism of N 2 O formation during nitrification. Previous research has demonstrated that manganese dioxide (MnO 2 ) and organic matter (OM) content of soil as well as soil pH are important control variables of N 2 O formation in the soil. But until now, their combined effect on abiotic N 2 O formation from NH 2 OH has not been quantified. Here, we present results from a full-factorial experiment with artificial soil mixtures at five different levels of pH, MnO 2 and OM, respectively, and quantified the interactive effects of the three variables on the NH 2 OH-to-N 2 O conversion ratio (R NH2OH-to-N2O ). Furthermore, the effect of OM quality on R NH2OH-to-N2O was determined by the addition of four different organic materials with different C/N ratios to the artificial soil mixtures. The experiments revealed a strong interactive effect of soil pH, MnO 2 and OM on R NH2OH-to-N2O . In general, increasing MnO 2 and decreasing pH increased R NH2OH-to-N2O , while increasing OM content was associated with a decrease in R NH2OH-to-N2O . Organic matter quality also affected R NH2OH-to-N2O . However, this effect was not a function of C/N ratio, but was rather related to differences in the dominating functional groups between the different organic materials.

Interactive effects of MnO2, organic matter and pH on abiotic formation of N2O from hydroxylamine in artificial soil mixtures

NASA Astrophysics Data System (ADS)

Liu, Shurong; Berns, Anne E.; Vereecken, Harry; Wu, Di; Brüggemann, Nicolas

2017-02-01

Abiotic conversion of the reactive nitrification intermediate hydroxylamine (NH2OH) to nitrous oxide (N2O) is a possible mechanism of N2O formation during nitrification. Previous research has demonstrated that manganese dioxide (MnO2) and organic matter (OM) content of soil as well as soil pH are important control variables of N2O formation in the soil. But until now, their combined effect on abiotic N2O formation from NH2OH has not been quantified. Here, we present results from a full-factorial experiment with artificial soil mixtures at five different levels of pH, MnO2 and OM, respectively, and quantified the interactive effects of the three variables on the NH2OH-to-N2O conversion ratio (RNH2OH-to-N2O). Furthermore, the effect of OM quality on RNH2OH-to-N2O was determined by the addition of four different organic materials with different C/N ratios to the artificial soil mixtures. The experiments revealed a strong interactive effect of soil pH, MnO2 and OM on RNH2OH-to-N2O. In general, increasing MnO2 and decreasing pH increased RNH2OH-to-N2O, while increasing OM content was associated with a decrease in RNH2OH-to-N2O. Organic matter quality also affected RNH2OH-to-N2O. However, this effect was not a function of C/N ratio, but was rather related to differences in the dominating functional groups between the different organic materials.

Low-temperature molar heat capacities and entropies of MnO2 (pyrolusite), Mn3O4 (hausmanite), and Mn2O3 (bixbyite)

USGS Publications Warehouse

Robie, R.A.; Hemingway, B.S.

1985-01-01

Pyrolusite (MnO2), hausmanite (Mn3O4), and bixbyite (Mn2O3), are important ore minerals of manganese and accurate values for their thermodynamic properties are desirable to understand better the {p(O2), T} conditions of their formation. To provide accurate values for the entropies of these important manganese minerals, we have measured their heat capacities between approximately 5 and 380 K using a fully automatic adiabatically-shielded calorimeter. All three minerals are paramagnetic above 100 K and become antiferromagnetic or ferrimagnetic at lower temperatures. This transition is expressed by a sharp ??-type anomaly in Cpmo for each compound with Ne??el temperatures TN of (92.2??0.2), (43.1??0.2), and (79.45??0.05) K for MnO2, Mn3O4, and Mn2O3, respectively. In addition, at T ??? 308 K, Mn2O3 undergoes a crystallographic transition, from orthorhombic (at low temperatures) to cubic. A significant thermal effect is associated with this change. Hausmanite is ferrimagnetic below TN and in addition to the normal ??-shape of the heat-capacity maxima in MnO2 and Mn2O3, it has a second rounded maximum at 40.5 K. The origin of this subsidiary bump in the heat capacity is unknown but may be related to a similar "anomalous bump" in the curve of magnetization against temperature at about 39 K observed by Dwight and Menyuk.(1) At 298.15 K the standard molar entropies of MnO2, Mn3O4, and Mn2O3, are (52.75??0.07), (164.1??0.2), and (113.7??0.2) J??K-1??mol-1, respectively. Our value for Mn3O4 is greater than that adopted in the National Bureau of Standards tables(2) by 14 per cent. ?? 1985.

Enhanced permanganate in situ chemical oxidation through MnO2 particle stabilization: evaluation in 1-D transport systems.

PubMed

Crimi, Michelle; Quickel, Mark; Ko, Saebom

2009-02-27

In situ chemical oxidation using permanganate is an increasingly employed approach to organic contaminant remediation at hazardous waste sites. Manganese dioxide (MnO2) particles form as a by-product of the reaction of permanganate with contaminants and naturally-reduced subsurface materials. These particles are of interest because they have the potential to deposit in the subsurface and impact the flow regime in/around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. Control of these particles can allow for improved oxidant injection and transport, and contact between the oxidant and contaminants of concern. Sodium hexametaphosphate (HMP) has previously been identified as a promising aid to stabilize MnO2 in solution when included in the oxidizing solution, increasing the potential to inhibit particle deposition and impact subsurface flow. The goal of the experimental studies described herein was to investigate the ability of HMP to prevent particle deposition in transport studies using four different types of porous media. Permanganate was delivered to a contaminant source zone (trichloroethylene) located within four different media types with variations in sand, clay, organic carbon, and iron oxides (as goethite) content. Deposition of MnO2 within the columns was quantified with distance from the source zone. Experiments were repeated in replicate columns with the inclusion of HMP directly with the oxidant delivery solution, and MnO2 deposition was again quantified. While total MnO2 deposition within the 60 cm columns did not change significantly with the addition of HMP, deposition within the contaminant source zone decreased by 25-85%, depending on the specific media type. The greatest differences in deposition were observed in the goethite-containing and clay-containing columns. Columns containing these two media types experienced completely plugged flow in the oxidant-only delivery systems; however

Nanotubular MnO2/graphene oxide composites for the application of open air-breathing cathode microbial fuel cells.

PubMed

Gnana Kumar, G; Awan, Zahoor; Suk Nahm, Kee; Xavier, J Stanley

2014-03-15

Nanotubular shaped α-MnO2/graphene oxide nanocomposites were synthesized via a simple, cost and time efficient hydrothermal method. The growth of hollow structured MnO2 nanotubes preferentially occurred along the [001] direction as evidenced from the morphological and structural characterizations. The tunnels of α-MnO2 nanotubes easily accommodated the molecular oxygen and exhibited excellent catalytic activity towards the oxygen reduction reaction over the rod structure and was further enhanced with the effective carbon support graphene oxide. The MnO2 nanotubes/graphene oxide nanocomposite modified electrode exhibited a maximum power density of 3359 mW m(-2) which is 7.8 fold higher than that of unmodified electrode and comparable with the Pt/C modified electrode. The microbial fuel cell equipped with MnO2 nanotubes/graphene oxide nanocomposite modified cathode exhibited quick start up and excellent durability over the studied electrodes and is attributed to the high surface area and number of active sites. These findings not only provide the fundamental studies on carbon supported low-dimensional transition-metal oxides but also open up the new possibilities of their applications in green energy devices. © 2013 Elsevier B.V. All rights reserved.

Simulation of First-Charge Oxygen-Dimerization and Mn-Migration in Li-Rich Layered Oxides xLi 2MnO 3 ·(1 – x )Li MO 2 and Implications for Voltage Fade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benedek, Roy; Iddir, Hakim

The instabilities of Li-rich layered oxide xLi 2MnO 3•(1-x)LiMO 2 (lithium-ion-battery cathode materials) during the first charge are investigated using first-principles dynamical simulation. To complement our earlier simulations for (x = 0.4, M = Ni 0.5Mn 0.5), we address here: pure Li 2MnO 3; small x; M compositions that include Co; a composite with Co spinel: Li 2MnO 3•Li 2M 2O 4; a Li 2MnO 3 slab. Lastly, we discuss how the threshold fraction f of Li 2(1-f)MnO 3 delithiation at which instabilities occur at the surface, fth(surface), differs from that in the bulk, f th(bulk). Approaches to inhibit voltagemore » fade are discussed.« less

Simulation of First-Charge Oxygen-Dimerization and Mn-Migration in Li-Rich Layered Oxides xLi 2MnO 3 ·(1 – x )Li MO 2 and Implications for Voltage Fade

DOE PAGES

Benedek, Roy; Iddir, Hakim

2017-03-08

The instabilities of Li-rich layered oxide xLi 2MnO 3•(1-x)LiMO 2 (lithium-ion-battery cathode materials) during the first charge are investigated using first-principles dynamical simulation. To complement our earlier simulations for (x = 0.4, M = Ni 0.5Mn 0.5), we address here: pure Li 2MnO 3; small x; M compositions that include Co; a composite with Co spinel: Li 2MnO 3•Li 2M 2O 4; a Li 2MnO 3 slab. Lastly, we discuss how the threshold fraction f of Li 2(1-f)MnO 3 delithiation at which instabilities occur at the surface, fth(surface), differs from that in the bulk, f th(bulk). Approaches to inhibit voltagemore » fade are discussed.« less

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Xiong, Qinqin; Zheng, Cun; Chi, Hongzhong; Zhang, Jun; Ji, Zhenguo

2017-02-01

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO2 nanotubes are used as the skeleton core for assembly of electrodeposited MnO2-C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO2/MnO2-C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g-1 at 2.5 A g-1), excellent rate properties (735 F g-1 at 30 A g-1) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes.

PubMed

Xiong, Qinqin; Zheng, Cun; Chi, Hongzhong; Zhang, Jun; Ji, Zhenguo

2017-02-03

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO 2 nanotubes are used as the skeleton core for assembly of electrodeposited MnO 2 -C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO 2 /MnO 2 -C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g -1 at 2.5 A g -1 ), excellent rate properties (735 F g -1 at 30 A g -1 ) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

Removal of Congo red dye molecules by MnO2 nanorods.

PubMed

Yin, Bosi; Zhang, Siwen; Jiao, Yang; Liu, Yang; Qu, Fengyu; Ma, Yajie; Wu, Xiang

2014-09-01

Uniform MnO2 nanorods were synthesized successfully via a facile and effective hydrothermal approach. Scanning electron microscope images showed that the average diameter of the as-synthesized nanorod is about 30 nm and the length of that is about 5 μm, respectively. Photocatalytic experimental results indicate that Congo red can be degraded nearly completely (over 97%) after visible light irradiation of 120 min, demonstrating potential applications of such nanorod structures for wastewater purification.

Co3O4/MnO2/Hierarchically Porous Carbon as Superior Bifunctional Electrodes for Liquid and All-Solid-State Rechargeable Zinc-Air Batteries.

PubMed

Li, Xuemei; Dong, Fang; Xu, Nengneng; Zhang, Tao; Li, Kaixi; Qiao, Jinli

2018-05-09

The design of efficient, durable, and affordable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very indispensable in liquid-type and flexible all-solid-state zinc-air batteries. Herein, we present a high-performance bifunctional catalyst with cobalt and manganese oxides supported on porous carbon (Co 3 O 4 /MnO 2 /PQ-7). The optimized Co 3 O 4 /MnO 2 /PQ-7 exhibited a comparable ORR performance with commercial Pt/C and a more superior OER performance than all of the other prepared catalysts, including commercial Pt/C. When applied to practical aqueous (6.0 M KOH) zinc-air batteries, the Co 3 O 4 /MnO 2 /porous carbon hybrid catalysts exhibited exceptional performance, such as a maximum discharge peak power density as high as 257 mW cm -2 and the most stable charge-discharge durability over 50 h with negligible deactivation to date. More importantly, a series of flexible all-solid-state zinc-air batteries can be fabricated by the Co 3 O 4 /MnO 2 /porous carbon with a layer-by-layer method. The optimal catalyst (Co 3 O 4 /MnO 2 /PQ-7) exhibited an excellent peak power density of 45 mW cm -2 . The discharge potentials almost remained unchanged for 6 h at 5 mA cm -2 and possessed a long cycle life (2.5 h@5 mA cm -2 ). These results make the optimized Co 3 O 4 /MnO 2 /PQ-7 a promising cathode candidate for both liquid-type and flexible all-solid-state zinc-air batteries.

Interlinked multiphase Fe-doped MnO2 nanostructures: a novel design for enhanced pseudocapacitive performance

NASA Astrophysics Data System (ADS)

Wang, Ziya; Wang, Fengping; Li, Yan; Hu, Jianlin; Lu, Yanzhen; Xu, Mei

2016-03-01

Structure designing and morphology control can lead to high performance pseudocapacitive materials for supercapacitors. In this work, we have designed interlinked multiphase Fe-doped MnO2 nanostructures (α-MnO2/R-MnO2/ε-MnO2) to enhance the electrochemical properties by a facile method. These hierarchical hollow microspheres assembled by interconnected nanoflakes, and with plenty of porous nanorods radiating from the spherical shells were hydrothermally obtained. The supercapacitor electrode prepared from the unique construction exhibits outstanding specific capacitance of 267.0 F g-1 even under a high mass loading (~5 mg cm-2). Obviously improved performances compared to pure MnO2 are also demonstrated with a good rate capability, high energy density (1.30 mW h cm-3) and excellent cycling stability of 100% capacitance retention after 2000 cycles at 2 A g-1. The synergistic effects of alternative crystal structures, appropriate crystallinity and optimal morphology are identified to be responsible for the observations. This rational multiphase composite strategy provides a promising idea for materials scientists to design and prepare scalable electrode materials for energy storage devices.Structure designing and morphology control can lead to high performance pseudocapacitive materials for supercapacitors. In this work, we have designed interlinked multiphase Fe-doped MnO2 nanostructures (α-MnO2/R-MnO2/ε-MnO2) to enhance the electrochemical properties by a facile method. These hierarchical hollow microspheres assembled by interconnected nanoflakes, and with plenty of porous nanorods radiating from the spherical shells were hydrothermally obtained. The supercapacitor electrode prepared from the unique construction exhibits outstanding specific capacitance of 267.0 F g-1 even under a high mass loading (~5 mg cm-2). Obviously improved performances compared to pure MnO2 are also demonstrated with a good rate capability, high energy density (1.30 mW h cm-3) and

Hierarchical 3D NiFe2O4@MnO2 core-shell nanosheet arrays on Ni foam for high-performance asymmetric supercapacitors.

PubMed

Zhang, Xinyang; Zhang, Ziqing; Sun, Shuanggan; Sun, Qiushi; Liu, Xiaoyang

2018-02-13

Hierarchical NiFe 2 O 4 @MnO 2 core-shell nanosheet arrays (NSAs) were synthesized on Ni foam as an integrated electrode for supercapacitors, using a facile two-step hydrothermal method followed by calcination treatment. The NiFe 2 O 4 nanosheets were designed as the core and ultrathin MnO 2 nanoflakes as the shell, creating a unique three-dimensional (3D) hierarchical electrode on Ni foam. The composite electrode exhibited remarkable electrochemical performance with a high specific capacitance of 1391 F g -1 at a current density of 2 mA cm -2 and long cycling stability at a high current density of 10 mA cm -2 (only 11.4% loss after 3000 cycles). Additionally, an asymmetric supercapacitor (ASC) device was fabricated with a NiFe 2 O 4 @MnO 2 composite as the positive electrode material and activated carbon (AC) as the negative one. The ASC device exhibited a high energy density (45.2 W h kg -1 ) at a power density of 174 W kg -1 , and an excellent cycling stability over 3000 cycles with 92.5% capacitance retention. The remarkable electrochemical performance demonstrated its great potential as a promising candidate for high-performance supercapacitors.

The morphology and electromagnetic properties of MnO 2 obtained in 8 T high magnetic field

NASA Astrophysics Data System (ADS)

Jia, Zhang; Yuping, Duan; Hui, Jing; Xiaogang, Li; Shunhua, Liu

2010-09-01

MnO 2 powder was synthesized in a high magnetic field (8 T) via a simple route, and the formation mechanism for the grain shape was discussed. The synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The morphology of synthesized MnO 2 was sea urchin-like ball chain with a low density center, just like "hollow-like". Throughout the whole frequency range, the dielectric constant and the loss tangent clearly decreased in 8 T high magnetic field. Moreover, the magnetic permeability and the loss tangent increased slightly in the frequency range 2-13 GHz. Furthermore, the theoretically calculated values of reflection loss showed that when the magnetic field strength 8 T was adopted, the absorption peak became smoother and shifted to a higher frequency.

Oxidation of MnO(100) and NaMnO2 formation: Characterization of Mn2+ and Mn3+ surfaces via XPS and water TPD

NASA Astrophysics Data System (ADS)

Feng, Xu; Cox, David F.

2018-09-01

The oxidation of clean and Na precovered MnO(100) has been investigated by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD) of adsorbed water. XPS results indicate that Mn3O4-like and Mn2O3-like surfaces can be formed by various oxidation treatments of clean and nearly-stoichiometric MnO(100), while a NaMnO2-like surface can be produced by the oxidation of MnO(100) pre-covered with multilayers of metallic Na. Water TPD results indicate that water adsorption/desorption is sensitive to the available oxidation states of surface Mn cations, and can be used to distinguish between surfaces exposing Mn2+and Mn3+ cations, or a combination of these oxidation states. Carbon dioxide and water TPD results from the NaMnO2-like surface indicate that pre-adsorbed water blocks the uptake of CO2, while water displaces pre-adsorbed CO2. No indication of a strong reactive interaction is observed between CO2, water and the NaMnO2-like surface under the conditions of our study.

Low-cost flexible supercapacitors with high-energy density based on nanostructured MnO2 and Fe2O3 thin films directly fabricated onto stainless steel.

PubMed

Gund, Girish S; Dubal, Deepak P; Chodankar, Nilesh R; Cho, Jun Y; Gomez-Romero, Pedro; Park, Chan; Lokhande, Chandrakant D

2015-07-24

The facile and economical electrochemical and successive ionic layer adsorption and reaction (SILAR) methods have been employed in order to prepare manganese oxide (MnO2) and iron oxide (Fe2O3) thin films, respectively with the fine optimized nanostructures on highly flexible stainless steel sheet. The symmetric and asymmetric flexible-solid-state supercapacitors (FSS-SCs) of nanostructured (nanosheets for MnO2 and nanoparticles for Fe2O3) electrodes with Na2SO4/Carboxymethyl cellulose (CMC) gel as a separator and electrolyte were assembled. MnO2 as positive and negative electrodes were used to fabricate symmetric SC, while the asymmetric SC was assembled by employing MnO2 as positive and Fe2O3 as negative electrode. Furthermore, the electrochemical features of symmetric and asymmetric SCs are systematically investigated. The results verify that the fabricated symmetric and asymmetric FSS-SCs present excellent reversibility (within the voltage window of 0-1 V and 0-2 V, respectively) and good cycling stability (83 and 91%, respectively for 3000 of CV cycles). Additionally, the asymmetric SC shows maximum specific capacitance of 92 Fg(-1), about 2-fold of higher energy density (41.8 Wh kg(-1)) than symmetric SC and excellent mechanical flexibility. Furthermore, the "real-life" demonstration of fabricated SCs to the panel of SUK confirms that asymmetric SC has 2-fold higher energy density compare to symmetric SC.

Low-cost flexible supercapacitors with high-energy density based on nanostructured MnO2 and Fe2O3 thin films directly fabricated onto stainless steel

PubMed Central

Gund, Girish S.; Dubal, Deepak P.; Chodankar, Nilesh R.; Cho, Jun Y.; Gomez-Romero, Pedro; Park, Chan; Lokhande, Chandrakant D.

2015-01-01

The facile and economical electrochemical and successive ionic layer adsorption and reaction (SILAR) methods have been employed in order to prepare manganese oxide (MnO2) and iron oxide (Fe2O3) thin films, respectively with the fine optimized nanostructures on highly flexible stainless steel sheet. The symmetric and asymmetric flexible-solid-state supercapacitors (FSS-SCs) of nanostructured (nanosheets for MnO2 and nanoparticles for Fe2O3) electrodes with Na2SO4/Carboxymethyl cellulose (CMC) gel as a separator and electrolyte were assembled. MnO2 as positive and negative electrodes were used to fabricate symmetric SC, while the asymmetric SC was assembled by employing MnO2 as positive and Fe2O3 as negative electrode. Furthermore, the electrochemical features of symmetric and asymmetric SCs are systematically investigated. The results verify that the fabricated symmetric and asymmetric FSS-SCs present excellent reversibility (within the voltage window of 0–1 V and 0–2 V, respectively) and good cycling stability (83 and 91%, respectively for 3000 of CV cycles). Additionally, the asymmetric SC shows maximum specific capacitance of 92 Fg−1, about 2-fold of higher energy density (41.8 Wh kg−1) than symmetric SC and excellent mechanical flexibility. Furthermore, the “real-life” demonstration of fabricated SCs to the panel of SUK confirms that asymmetric SC has 2-fold higher energy density compare to symmetric SC. PMID:26208144

Low-cost flexible supercapacitors with high-energy density based on nanostructured MnO2 and Fe2O3 thin films directly fabricated onto stainless steel

NASA Astrophysics Data System (ADS)

Gund, Girish S.; Dubal, Deepak P.; Chodankar, Nilesh R.; Cho, Jun Y.; Gomez-Romero, Pedro; Park, Chan; Lokhande, Chandrakant D.

2015-07-01

The facile and economical electrochemical and successive ionic layer adsorption and reaction (SILAR) methods have been employed in order to prepare manganese oxide (MnO2) and iron oxide (Fe2O3) thin films, respectively with the fine optimized nanostructures on highly flexible stainless steel sheet. The symmetric and asymmetric flexible-solid-state supercapacitors (FSS-SCs) of nanostructured (nanosheets for MnO2 and nanoparticles for Fe2O3) electrodes with Na2SO4/Carboxymethyl cellulose (CMC) gel as a separator and electrolyte were assembled. MnO2 as positive and negative electrodes were used to fabricate symmetric SC, while the asymmetric SC was assembled by employing MnO2 as positive and Fe2O3 as negative electrode. Furthermore, the electrochemical features of symmetric and asymmetric SCs are systematically investigated. The results verify that the fabricated symmetric and asymmetric FSS-SCs present excellent reversibility (within the voltage window of 0-1 V and 0-2 V, respectively) and good cycling stability (83 and 91%, respectively for 3000 of CV cycles). Additionally, the asymmetric SC shows maximum specific capacitance of 92 Fg-1, about 2-fold of higher energy density (41.8 Wh kg-1) than symmetric SC and excellent mechanical flexibility. Furthermore, the “real-life” demonstration of fabricated SCs to the panel of SUK confirms that asymmetric SC has 2-fold higher energy density compare to symmetric SC.

Introducing Ratiometric Fluorescence to MnO2 Nanosheet-Based Biosensing: A Simple, Label-Free Ratiometric Fluorescent Sensor Programmed by Cascade Logic Circuit for Ultrasensitive GSH Detection.

PubMed

Fan, Daoqing; Shang, Changshuai; Gu, Wenling; Wang, Erkang; Dong, Shaojun

2017-08-09

Glutathione (GSH) plays crucial roles in various biological functions, the level alterations of which have been linked to varieties of diseases. Herein, we for the first time expanded the application of oxidase-like property of MnO 2 nanosheet (MnO 2 NS) to fluorescent substrates of peroxidase. Different from previously reported fluorescent quenching phenomena, we found that MnO 2 NS could not only largely quench the fluorescence of highly fluorescent Scopoletin (SC) but also surprisingly enhance that of nonfluorescent Amplex Red (AR) via oxidation reaction. If MnO 2 NS is premixed with GSH, it will be reduced to Mn 2+ and lose the oxidase-like property, accompanied by subsequent increase in SC's fluorescence and decrease in AR's. On the basis of the above mechanism, we construct the first MnO 2 NS-based ratiometric fluorescent sensor for ultrasensitive and selective detection of GSH. Notably, this ratiometric sensor is programmed by the cascade logic circuit (an INHIBIT gate cascade with a 1 to 2 decoder). And a linear relationship between ratiometric fluorescent intensities of the two substrates and logarithmic values of GSH's concentrations is obtained. The detection limit of GSH is as low as 6.7 nM, which is much lower than previous ratiometric fluorescent sensors, and the lowest MnO 2 NS-based fluorescent GSH sensor reported so far. Furthermore, this sensor is simple, label-free, and low-cost; it also presents excellent applicability in human serum samples.

A high performance flexible all solid state supercapacitor based on the MnO2 sphere coated macro/mesoporous Ni/C electrode and ionic conducting electrolyte

NASA Astrophysics Data System (ADS)

Zhi, Jian; Reiser, Oliver; Wang, Youfu; Hu, Aiguo

2016-06-01

A high contact resistance between the active materials and the current collector, a low ionic conductivity of the gel electrolyte, and an impenetrable electrode structure are the three major barriers which greatly limit the capacitance of MnO2 in solid state supercapacitors. As a potential solution to these problems, in this work we report a novel electrode for solid state supercapacitors, based on a ternary system composed of hierarchical MnO2 spheres as the active material, macroporous Ni foam as gel penetrable skeletons and an ordered mesoporous carbon (OMC) membrane as the charge-transport accelerating layer. By employing butyl-3-methylimidazolium chloride (BMIMCl) modified gels as the ionic conducting electrolyte, the utilization efficiency of MnO2 on the specific capacitance was enhanced up to 88% of the theoretical value, delivering a volumetric capacitance of 81 F cm-3, which is the highest value among MnO2 based solid state supercapacitors. Moreover, such a flexible device exhibits exceptional volumetric energy and power density (6.6 Wh L-1 and 549 W L-1, based on the whole device volume) combined with a small capacity loss of 8.5% after 6000 cycles under twisting. These encouraging findings unambiguously overcome the energy bottleneck of MnO2 in solid state supercapacitors, and open up a new application of macro/mesoporous materials in flexible devices.A high contact resistance between the active materials and the current collector, a low ionic conductivity of the gel electrolyte, and an impenetrable electrode structure are the three major barriers which greatly limit the capacitance of MnO2 in solid state supercapacitors. As a potential solution to these problems, in this work we report a novel electrode for solid state supercapacitors, based on a ternary system composed of hierarchical MnO2 spheres as the active material, macroporous Ni foam as gel penetrable skeletons and an ordered mesoporous carbon (OMC) membrane as the charge-transport accelerating

Persulfate activation by iron oxide-immobilized MnO2 composite: identification of iron oxide and the optimum pH for degradations.

PubMed

Jo, Young-Hoon; Do, Si-Hyun; Kong, Sung-Ho

2014-01-01

Iron oxide-immobilized manganese oxide (MnO2) composite was prepared and the reactivity of persulfate (PS) with the composite as activator was investigated for degradation of carbon tetrachloride and benzene at various pH levels. Brunauer-Emmett-Teller (BET) surface area of the composite was similar to that of pure MnO2 while the pore volume and diameter of composite was larger than those of MnO2. Scanning electron microscopy couples with energy dispersive spectroscopy (SEM-EDS) showed that Fe and Mn were detected on the surface of the composite, and X-ray diffraction (XRD) analysis indicated the possibilities of the existence of various iron oxides on the composite surface. Furthermore, the analyses of X-ray photoelectron (XPS) spectra revealed that the oxidation state of iron was identified as 1.74. In PS/composite system, the same pH for the highest degradation rates of both carbon tetrachloride and benzene were observed and the value of pH was 9. Scavenger test was suggested that both oxidants (i.e. hydroxyl radical, sulfate radical) and reductant (i.e. superoxide anion) were effectively produced when PS was activated with the iron-immobilized MnO2. Copyright © 2013 Elsevier Ltd. All rights reserved.

Monodisperse MnO2@NiCo2O4 core/shell nanospheres with highly opened structures as electrode materials for good-performance supercapacitors

NASA Astrophysics Data System (ADS)

Zhou, You; Ma, Li; Gan, Mengyu; Ye, Menghan; Li, Xiurong; Zhai, Yanfang; Yan, Fabing; Cao, Feifei

2018-06-01

The monodisperse MnO2@NiCo2O4 core/shell nanospheres for good-performance supercapacitors are designed and synthesized by a two-step solution-based method and a simple post annealing process. In the composite, both MnO2 (the "core") and NiCo2O4 (the "shell") are formed by the accumulation of nanoflakes. Thus, nearly all the core/shell nanoflakes are highly opened and accessible to electrolyte, making them give full play to the Faradaic reaction. Our results demonstrate that the composite electrode exhibits desirable pseudocapacitive behaviors with higher specific capacitance (1127.27 F g-1 at a current density of 1 A g-1), better rate capability (81.0% from 1 to 16 A g-1) and superior cycling stability (actually 126.8% capacitance retention after 1000 cycles and only 3.7% loss after 10,000 cycles at 10 A g-1) in 3 M KOH aqueous solution. Moreover, it offers the excellent specific energy density of 26.6 Wh kg-1 at specific power density of 800 W kg-1. The present MnO2@NiCo2O4 core/shell nanospheres with remarkable electrochemical properties are considered as potential electrode materials for the next generation supercapacitors.

Peatland Acidobacteria with a dissimilatory sulfur metabolism.

PubMed

Hausmann, Bela; Pelikan, Claus; Herbold, Craig W; Köstlbacher, Stephan; Albertsen, Mads; Eichorst, Stephanie A; Glavina Del Rio, Tijana; Huemer, Martin; Nielsen, Per H; Rattei, Thomas; Stingl, Ulrich; Tringe, Susannah G; Trojan, Daniela; Wentrup, Cecilia; Woebken, Dagmar; Pester, Michael; Loy, Alexander

2018-02-23

Sulfur-cycling microorganisms impact organic matter decomposition in wetlands and consequently greenhouse gas emissions from these globally relevant environments. However, their identities and physiological properties are largely unknown. By applying a functional metagenomics approach to an acidic peatland, we recovered draft genomes of seven novel Acidobacteria species with the potential for dissimilatory sulfite (dsrAB, dsrC, dsrD, dsrN, dsrT, dsrMKJOP) or sulfate respiration (sat, aprBA, qmoABC plus dsr genes). Surprisingly, the genomes also encoded DsrL, which so far was only found in sulfur-oxidizing microorganisms. Metatranscriptome analysis demonstrated expression of acidobacterial sulfur-metabolism genes in native peat soil and their upregulation in diverse anoxic microcosms. This indicated an active sulfate respiration pathway, which, however, might also operate in reverse for dissimilatory sulfur oxidation or disproportionation as proposed for the sulfur-oxidizing Desulfurivibrio alkaliphilus. Acidobacteria that only harbored genes for sulfite reduction additionally encoded enzymes that liberate sulfite from organosulfonates, which suggested organic sulfur compounds as complementary energy sources. Further metabolic potentials included polysaccharide hydrolysis and sugar utilization, aerobic respiration, several fermentative capabilities, and hydrogen oxidation. Our findings extend both, the known physiological and genetic properties of Acidobacteria and the known taxonomic diversity of microorganisms with a DsrAB-based sulfur metabolism, and highlight new fundamental niches for facultative anaerobic Acidobacteria in wetlands based on exploitation of inorganic and organic sulfur molecules for energy conservation.

Enhancing pseudocapacitive kinetics of nanostructured MnO2 through anchoring onto biomass-derived porous carbon

NASA Astrophysics Data System (ADS)

Chen, Qiongyu; Chen, Jizhang; Zhou, Yuyang; Song, Chao; Tian, Qinghua; Xu, Junling; Wong, Ching-Ping

2018-05-01

The rational construction of heterostructured electrode materials that deliver superior performances to their individual counterparts offers an attractive strategy for supercapacitors. Herein, we anchor low-crystalline nanostructured MnO2 onto soybean stalk-derived carbon matrix through chemical activation and subsequent hydrothermal reaction. The highly porous and conductive matrix can effectively enhance pseudocapacitive kinetics of nanostructured MnO2. Therefore, the obtained nanocomposite exhibits high specific capacitance (384.9 F g-1 at a current density of 0.5 A g-1), great rate capability (185.0 F g-1 at 20 A g-1), and superior cyclability (90.7% capacitance retention after 5000 cycles). Using this nanocomposite as the positive electrode material, an asymmetric supercapacitor (ASC) is assembled, and achieves high specific energy of 34.2 Wh kg-1 and high specific power of 9.58 kW kg-1. The results of this study demonstrate great potential of combining biomass-derived porous carbon with metal oxides.

Oxidation of Benzoin to Benzil Using Alumina-Supported Active MnO2

NASA Astrophysics Data System (ADS)

Crouch, R. David; Holden, Michael S.; Burger, Jennifer S.

2001-07-01

The use of alumina-supported active MnO2 to oxidize benzoin to benzil is described. The advantages of this reagent include ease of handling and separation from the product and lower toxicity than previously reported supported oxidizing agents. The product is purified by elution through a simple chromatography column consisting of a silica gel-packed Pasteur pipet. Students' yields are comparable to yields from other reported oxidation methods.

Control of Low Melting Point Mno-Sio2-Al2o3 Inclusions in Low Carbon Thin-Strip Continuous Casting Steel

NASA Astrophysics Data System (ADS)

Chen, Jing; Zhu, Qing; Huang, Di; Zheng, Shaobo; Zhang, Jieyu; Li, Huigai

2017-09-01

There is a significant difference in the demand for molten steel quality between thin-strip continuous casting and traditional continuous casting. In order to make sure the better surface quality of the thin strips, to generate an oxidation film on the surface of cooling roller is required. This will require that the higher oxygen potential in molten steel and inclusions with low melting point. In this article, the possibility of producing low-melting inclusions which is mainly consisted of SiO2 and MnO is studied by controlling the initial oxygen potential and addition order of deoxidizing alloys. The interaction activity between each component in the ternary system of Al2O3-SiO2-MnO is obtained by Action Concentration model. The equal [Mn], [Si], [O], [Al] curve under the temperature of 1823K and equilibrium condition in ternary system of Al2O3-SiO2-MnO is obtained by relative thermodynamic calculation as well. The control method for getting the low-melting point inclusion is as below. While the weight percentage of Si is 0.35% and the one of Mn is 0.90%, in order to maintain the melting point of inclusion around 1200°C, the free oxygen potential in melted steel F[O] should be maintained between 0.002% ∼ 0.004%. On the contrary, the requirement for acid dissolved [Al] content in melted steel is as low as 0.0001% ∼ 0.0005%.

Size-driven magnetic transitions in La1/3Ca2/3MnO3 nanoparticles

NASA Astrophysics Data System (ADS)

Markovich, V.; Fita, I.; Wisniewski, A.; Mogilyansky, D.; Puzniak, R.; Titelman, L.; Gorodetsky, G.

2010-09-01

Magnetic properties of electron-doped La1/3Ca2/3MnO3 manganite nanoparticles with average particle size ranging from 12 to 42 nm, prepared by the glycine-nitrate method, have been investigated in temperature range 5-300 K and in magnetic fields up to 90 kOe. Reduction in the particle size suppresses antiferromagnetism and decreases the Néel temperature. In contrast to bulk crystals, the charge ordering does not occur in all studied nanoparticles, while a weak ferromagnetism appears above 200 K. Low temperature magnetic hysteresis loops indicate upon exchange bias effect displayed by horizontal and vertical shifts in field cooled processes. The spontaneous and remanent magnetization at low temperature shows a relatively complex variation with particle size. The size-induced structural/magnetic disorder drives the La1/3Ca2/3MnO3 nanoparticles to a pronounced glassy behavior for the smallest 12 nm particles, as evidenced by large difference between zero field cooled and field cooled magnetization, frequency dependent ac-susceptibility, as well as characteristic slowing down in the spin dynamics. Time evolution of magnetization recorded in magnetic fields after field cooling to low temperatures exhibits pronounced relaxation and a very noisy behavior that may be caused by formation of some collective states. Magnetic properties of the nanoparticle samples are compared with those of La0.2Ca0.8MnO3 nanoparticles. These results shed some light on the coupling between charges and spin degrees of freedom in antiferromagnetic manganite nanoparticles.

High-performance asymmetric supercapacitors based on multilayer MnO2 /graphene oxide nanoflakes and hierarchical porous carbon with enhanced cycling stability.

PubMed

Zhao, Yufeng; Ran, Wei; He, Jing; Huang, Yizhong; Liu, Zhifeng; Liu, Wei; Tang, Yongfu; Zhang, Long; Gao, Dawei; Gao, Faming

2015-03-18

In this work, MnO(2)/GO (graphene oxide) composites with novel multilayer nanoflake structure, and a carbon material derived from Artemia cyst shell with genetic 3D hierarchical porous structure (HPC), are prepared. An asymmetric supercapacitor has been fabricated using MnO(2)/GO as positive electrode and HPC as negative electrode material. Because of their unique structures, both MnO(2)/GO composites and HPC exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high voltage range of 0-2 V in aqueous electrolyte, which exhibits maximum energy density of 46.7 Wh kg(-1) at a power density of 100 W kg(-1) and remains 18.9 Wh kg(-1) at 2000 W kg(-1). Additionally, such device also shows superior long cycle life along with ∼100% capacitance retention after 1000 cycles and ∼93% after 4000 cycles. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development and Long-Term Stability of a Novel Microbial Fuel Cell BOD Sensor with MnO2 Catalyst

PubMed Central

Kharkwal, Shailesh; Tan, Yi Chao; Lu, Min; Ng, How Yong

2017-01-01

A novel microbial fuel cell (MFC)-based biosensor was designed for continuous monitoring of biochemical oxygen demand (BOD) in real wastewater. To lower the material cost, manganese dioxide (MnO2) was tested as an innovative cathode catalyst for oxygen reduction in a single chamber air-cathode MFC, and two different crystalline structures obtained during synthesis of MnO2 (namely β- and γ-MnO2) were compared. The BOD sensor was studied in a comprehensive way, using both sodium acetate solution and real domestic wastewater (DWW). The optimal performance of the sensor was obtained with a β-MnO2 catalyst, with R2 values of 0.99 and 0.98 using sodium acetate solution and DWW, respectively. The BOD values predicted by the β-MnO2 biosensor for DWW were in agreement with the BOD5 values, determined according to standard methods, with slight variations in the range from 3% to 12%. Finally, the long-term stability of the BOD biosensor was evaluated over 1.5 years. To the best of our knowledge, this is the first report of an MFC BOD sensor using an MnO2 catalyst at the cathode; the feasibility of using a low-cost catalyst in an MFC for online measurement of BOD in real wastewater broadens the scope of applications for such devices. PMID:28134838

MnO2-Based Electrochemical Supercapacitors on Flexible Carbon Substrates

NASA Astrophysics Data System (ADS)

Tadjer, Marko J.; Mastro, Michael A.; Rojo, José M.; Mojena, Alberto Boscá; Calle, Fernando; Kub, Francis J.; Eddy, Charles R.

2014-04-01

Manganese dioxide films were grown on large area flexible carbon aerogel substrates. Characterization by x-ray diffraction confirmed α-MnO2 growth. Three types of films were compared as a function of hexamethylenetetramine (HMTA) concentration during growth. The highest concentration of HM TA produced MnO2 flower-like films, as observed by scanning electron microscopy, whose thickness and surface coverage lead to both a higher specific capacitance and higher series resistance. Specific capacitance was measured to be 64 F/g using a galvanostatic setup, compared to the 47 F/g-specific capacitance of the carbon aerogel substrate. Such supercapacitor devices can be fabricated on large area sheets of carbon aerogel to achieve high total capacitance.

Effective capture and release of circulating tumor cells using core-shell Fe3O4@MnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Xiao, Liang; He, Zhao-Bo; Cai, Bo; Rao, Lang; Cheng, Long; Liu, Wei; Guo, Shi-Shang; Zhao, Xing-Zhong

2017-01-01

Circulating tumor cells (CTCs) have been believed to hold significant insights for cancer diagnosis and therapy. Here, we developed a simple and effective method to capture and release viable CTCs using core-shell Fe3O4@MnO2 nanoparticles. Fe3O4@MnO2 nanoparticles bioconjugated with anti-EpCAM antibody have characteristics of specific recognition, magnetic-driven cell isolation and oxalic acid-assisted cell release. The capture and release efficiency of target cancer cells were ∼83% and ∼55%, respectively. And ∼70% of released cells kept good viability, which could facilitate the subsequent cellular analysis.

Synthesis and electrochemical performance of polyaniline @MnO2/graphene ternary composites for electrochemical supercapacitors

NASA Astrophysics Data System (ADS)

Pan, Chao; Gu, Haiteng; Dong, Li

2016-01-01

We introduce a facile method to construct new ternary hierarchical nanocomposites by combining MnO2 coated one dimensional (1D) conducting polyaniline (PANI) nanowires with 2D graphene sheets (GNs). The hierarchical nanocomposite structures of PANI@MnO2/GNs (PMGNs) are further proved by X-ray diffraction (XRD), FT-IR, field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The electrochemical characteristics of the electrodes made of the hierarchical structured PMGNs materials are determined by the CV and galvanostatic measurements. These electrochemical tests indicate that electrodes made of the nanostructured PMGNs exhibit an improved reversible capacitance of 695 F g-1 after 1000 cycles at a high current density of 4 A g-1. The ternary composites possess higher electrochemical capacitance than each individual component as supercapacitor electrode materials. Such intriguing electrochemical performance is mainly attributed to the synergistic effects of MnO2, PANI and graphene. The hierarchical ternary nanocomposites show excellent electrochemical properties for energy storage applications, which evidence their potential application as supercapacitors.

Electrochemical trapping of metastable Mn3+ ions for activation of MnO2 oxygen evolution catalysts.

PubMed

Morgan Chan, Zamyla; Kitchaev, Daniil A; Nelson Weker, Johanna; Schnedermann, Christoph; Lim, Kipil; Ceder, Gerbrand; Tumas, William; Toney, Michael F; Nocera, Daniel G

2018-06-05

Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn 3+ We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn 3+ may be introduced into MnO 2 by an electrochemically induced comproportionation reaction with Mn 2+ and that Mn 3+ persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn 3+ -activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments. Computational studies show that Mn 3+ is kinetically trapped in tetrahedral sites and in a fully oxidized structure, consistent with the reduction of coordination number observed in EXAFS. Although in a reduced state, computation shows that Mn 3+ states are stabilized relative to those of oxygen and that the highest occupied molecular orbital (HOMO) is thus dominated by oxygen states. Furthermore, the Mn 3+ (T d ) induces local strain on the oxide sublattice as observed in Raman spectra and results in a reduced gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). The confluence of a reduced HOMO-LUMO gap and oxygen-based HOMO results in the facilitation of OER on the application of anodic potentials to the δ-MnO 2 polymorph incorporating Mn 3+ ions.

Electrochemical Trapping of Metastable Mn3+ Ions for Activation of MnO2 Oxygen Evolution Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tumas, William; Chan, Zamyla Morgan; Kitchaev, Daniil A.

Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn3+. We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn3+ may be introduced into MnO2 by an electrochemically induced comproportionation reaction with Mn2+ and that Mn3+ persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn3+-activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments. Computational studies showmore » that Mn3+ is kinetically trapped in tetrahedral sites and in a fully oxidized structure, consistent with the reduction of coordination number observed in EXAFS. Although in a reduced state, computation shows that Mn3+ states are stabilized relative to those of oxygen and that the highest occupied molecular orbital (HOMO) is thus dominated by oxygen states. Furthermore, the Mn3+(Td) induces local strain on the oxide sublattice as observed in Raman spectra and results in a reduced gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). The confluence of a reduced HOMO-LUMO gap and oxygen-based HOMO results in the facilitation of OER on the application of anodic potentials to the d-MnO2 polymorph incorporating Mn3+ ions.« less

Effect of MgO and MnO on Phosphorus Utilization in P-Bearing Steelmaking Slag

NASA Astrophysics Data System (ADS)

Lin, Lu; Bao, Yan-Ping; Wang, Min; Li, Xiang

2016-04-01

In order to recycle the phosphorus in P-bearing converter slag and make it used as slag phosphate fertilizer, the effect of MgO and MnO in P-bearing steelmaking slag on phosphorus existence form, P2O5 solubility and magnetic separation behavior were researched systematically. The results show that the phosphorus in slag is mainly in the form of n2CaO · SiO2-3CaO · P2O5 (for short nC2S-C3P) solid solution in the P-rich phase for CaO-SiO2-FetO-P2O5-X (X stands for MgO and MnO, respectively). And the increasing of MgO and MnO content has no influence on precipitation of nC2S-C3P solid solution in slag, MnO and MgO mainly enter into RO phase and base phase to form MnFe2O4 and MgFe2O4, which has little effect on the P2O5 content of P-rich phase, so which has little effect on the degree of phosphorus enrichment and phosphorus occurrence form of the P-bearing slag. And adding MgO and MnO into CaO-SiO2-P2O5-Fe2O3 slag system can break the complex net structure formed by Si-O on certain degree, and also hinder the precipitation of β-Ca3(PO4)2 crystal with low citric acid solubility during the melting-cooling process. Therefore, adding appropriate MgO and MnO content into slag can improve the slag P2O5 solubility, but the effect of different amounts of MgO and MnO on the P2O5 solubility has little difference. Meanwhile, adding MgO and MnO into slag can improve the metallization of slag and magnetism of iron-rich phase, make the magnetic substances content increase and separation of phosphorus and iron incomplete, so it is adverse to phosphorus resources recovery from P-bearing slag by magnetic separation method. In order to recycle the phosphorus in P-bearing converter slag, the MgO and MnO content in the P-bearing slag should be controlled in the steelmaking process.

Interlinked multiphase Fe-doped MnO2 nanostructures: a novel design for enhanced pseudocapacitive performance.

PubMed

Wang, Ziya; Wang, Fengping; Li, Yan; Hu, Jianlin; Lu, Yanzhen; Xu, Mei

2016-04-07

Structure designing and morphology control can lead to high performance pseudocapacitive materials for supercapacitors. In this work, we have designed interlinked multiphase Fe-doped MnO2 nanostructures (α-MnO2/R-MnO2/ε-MnO2) to enhance the electrochemical properties by a facile method. These hierarchical hollow microspheres assembled by interconnected nanoflakes, and with plenty of porous nanorods radiating from the spherical shells were hydrothermally obtained. The supercapacitor electrode prepared from the unique construction exhibits outstanding specific capacitance of 267.0 F g(-1) even under a high mass loading (∼5 mg cm(-2)). Obviously improved performances compared to pure MnO2 are also demonstrated with a good rate capability, high energy density (1.30 mW h cm(-3)) and excellent cycling stability of 100% capacitance retention after 2000 cycles at 2 A g(-1). The synergistic effects of alternative crystal structures, appropriate crystallinity and optimal morphology are identified to be responsible for the observations. This rational multiphase composite strategy provides a promising idea for materials scientists to design and prepare scalable electrode materials for energy storage devices.

A high performance flexible all solid state supercapacitor based on the MnO2 sphere coated macro/mesoporous Ni/C electrode and ionic conducting electrolyte.

PubMed

Zhi, Jian; Reiser, Oliver; Wang, Youfu; Hu, Aiguo

2016-06-09

A high contact resistance between the active materials and the current collector, a low ionic conductivity of the gel electrolyte, and an impenetrable electrode structure are the three major barriers which greatly limit the capacitance of MnO2 in solid state supercapacitors. As a potential solution to these problems, in this work we report a novel electrode for solid state supercapacitors, based on a ternary system composed of hierarchical MnO2 spheres as the active material, macroporous Ni foam as gel penetrable skeletons and an ordered mesoporous carbon (OMC) membrane as the charge-transport accelerating layer. By employing butyl-3-methylimidazolium chloride (BMIMCl) modified gels as the ionic conducting electrolyte, the utilization efficiency of MnO2 on the specific capacitance was enhanced up to 88% of the theoretical value, delivering a volumetric capacitance of 81 F cm(-3), which is the highest value among MnO2 based solid state supercapacitors. Moreover, such a flexible device exhibits exceptional volumetric energy and power density (6.6 Wh L(-1) and 549 W L(-1), based on the whole device volume) combined with a small capacity loss of 8.5% after 6000 cycles under twisting. These encouraging findings unambiguously overcome the energy bottleneck of MnO2 in solid state supercapacitors, and open up a new application of macro/mesoporous materials in flexible devices.

A hybrid of MnO2 nanowires and MWCNTs as cathode of excellent rate capability for supercapacitors

NASA Astrophysics Data System (ADS)

Tang, W.; Hou, Y. Y.; Wang, X. J.; Bai, Y.; Zhu, Y. S.; Sun, H.; Yue, Y. B.; Wu, Y. P.; Zhu, K.; Holze, R.

2012-01-01

A hybrid of MnO2-nanowires and MWCNTs to be used as cathode in a supercapacitor with good electrochemical performance was prepared by a facile hydrothermal method. In this hybrid the α-MnO2 nanowires are well entangled with MWCNTs. The MWCNTs provide a network for fast electron transport whereas MnO2 nanowires show a fast redox response. Since gain/loss of both electrons and ions can be realized very rapidly at the same time, the hybrid has an excellent rate capability and delivers an energy density of 17.8 Wh kg-1 at 400 W kg-1, which is maintained almost constant even at 3340 W kg-1 in 0.5 M Li2SO4 aqueous electrolyte. The cycling behavior is very good even in the presence of oxygen. The data present great promise for the hybrid as a practical cathode material for aqueous supercapacitor.

Hierarchically porous MnO2 microspheres doped with homogeneously distributed Fe3O4 nanoparticles for supercapacitors.

PubMed

Zhu, Jian; Tang, Shaochun; Xie, Hao; Dai, Yuming; Meng, Xiangkang

2014-10-22

Hierarchically porous yet densely packed MnO2 microspheres doped with Fe3O4 nanoparticles are synthesized via a one-step and low-cost ultrasound assisted method. The scalable synthesis is based on Fe(2+) and ultrasound assisted nucleation and growth at a constant temperature in a range of 25-70 °C. Single-crystalline Fe3O4 particles of 3-5 nm in diameter are homogeneously distributed throughout the spheres and none are on the surface. A systematic optimization of reaction parameters results in isolated, porous, and uniform Fe3O4-MnO2 composite spheres. The spheres' average diameter is dependent on the temperature, and thus is controllable in a range of 0.7-1.28 μm. The involved growth mechanism is discussed. The specific capacitance is optimized at an Fe/Mn atomic ratio of r = 0.075 to be 448 F/g at a scan rate of 5 mV/s, which is nearly 1.5 times that of the extremely high reported value for MnO2 nanostructures (309 F/g). Especially, such a structure allows significantly improved stability at high charging rates. The composite has a capacitance of 367.4 F/g at a high scan rate of 100 mV/s, which is 82% of that at 5 mV/s. Also, it has an excellent cycling performance with a capacitance retention of 76% after 5000 charge/discharge cycles at 5 A/g.

Magnetocaloric effect study of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite

NASA Astrophysics Data System (ADS)

Das, Kalipada; Roy Chowdhury, R.; Midda, S.; Sen, Pintu; Das, I.

2018-03-01

The present study involves investigaton of magnetocaloric effect of Pr0.67Ca0.33MnO3-La0.67Sr0.33MnO3 nanocomposite materials above room temperature. From application point of view in magnetic refrigeration our study highlights the enhancement of operating temperature region compared to the well known La0.67Sr0.33MnO3 refrigerant material above room temperature. Comparison has also been made with the magnetocaloric properties of La0.67Sr0.33MnO3 nanomaterials. The modification of the magnetocaloric entropy changes (broadening of the temperature dependent magnetic entropy change) is addressed due to the effect of the gradual melting of antiferromagnetic charge ordered state of the Pr0.67Ca0.33MnO3 nanoparticles in such nanocomposite materials.

The Molecular Density of States in Bacterial Nanowires

PubMed Central

El-Naggar, Mohamed Y.; Gorby, Yuri A.; Xia, Wei; Nealson, Kenneth H.

2008-01-01

The recent discovery of electrically conductive bacterial appendages has significant physiological, ecological, and biotechnological implications, but the mechanism of electron transport in these nanostructures remains unclear. We here report quantitative measurements of transport across bacterial nanowires produced by the dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1, whose electron transport system is being investigated for renewable energy recovery in microbial fuel cells and bioremediation of heavy metals and radionuclides. The Shewanella nanowires display a surprising nonlinear electrical transport behavior, where the voltage dependence of the conductance reveals peaks indicating discrete energy levels with higher electronic density of states. Our results indicate that the molecular constituents along the Shewanella nanowires possess an intricate electronic structure that plays a role in mediating transport. PMID:18441026

Integration of MnO2 thin film and carbon nanotubes to three-dimensional carbon microelectrodes for electrochemical microcapacitors

NASA Astrophysics Data System (ADS)

Jiang, Shulan; Shi, Tielin; Liu, Dan; Long, Hu; Xi, Shuang; Wu, Fengshun; Li, Xiaoping; Xia, Qi; Tang, Zirong

2014-09-01

Large-scale three-dimensional (3D) hybrid microelectrodes have been fabricated through modified carbon microelectromechanical systems (Carbon-MEMS) process and electrochemical deposition method. Greatly improved electrochemical performance has been shown for the 3D photoresist-derived carbon microelectrodes with the integration of carbon nanotubes (CNTs) and manganese dioxide (MnO2). The electrochemical measurements of the microelectrodes indicate that the specific geometric capacitance can reach up to 238 mF cm-2 at the current density of 0.5 mA cm-2. The capacitance loss is less than 18.2% of the original value after 6000 charge-discharge cycles. This study shows that stacking of MnO2 film and integrating of CNTs to the 3D glassy carbon microelectrodes have great potential for on-chip microcapacitors as energy storage devices, and the presented approach is promising for large-scale and low-cost manufacturing.

Dissimilatory reduction of nitrate and nitrite in the bovine rumen: nitrous oxide production and effect of acetylene.

PubMed

Kaspar, H F; Tiedje, J M

1981-03-01

15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow. Ammonium was the only 15N-labeled end product of quantitative significance. Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 0.3% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced. Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced. Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide. It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat.

Dissimilatory nitrate reduction to nitrate, nitrous oxide, and ammonium by Pseudomonas putrefaciens.

PubMed

Samuelsson, M O

1985-10-01

The influence of redox potential on dissimilatory nitrate reduction to ammonium was investigated on a marine bacterium, Pseudomonas putrefaciens. Nitrate was consumed (3.1 mmol liter-1), and ammonium was produced in cultures with glucose and without sodium thioglycolate. When sodium thioglycolate was added, nitrate was consumed at a lower rate (1.1 mmol liter-1), and no significant amounts of nitrite or ammonium were produced. No growth was detected in glucose media either with or without sodium thioglycolate. When grown on tryptic soy broth, the production of nitrous oxide paralleled growth. In the same medium, but with sodium thioglycolate, nitrous oxide was first produced during growth and then consumed. Acetylene caused the nitrous oxide to accumulate. These results and the mass balance calculations for different nitrogen components indicate that P. putrefaciens has the capacity to dissimilate nitrate to ammonium as well as to dinitrogen gas and nitrous oxide (denitrification). The dissimilatory pathway to ammonium dominates except when sodium thioglycolate is added to the medium.

Bacterial Disproportionation of Elemental Sulfur Coupled to Chemical Reduction of Iron or Manganese

PubMed Central

Thamdrup, Bo; Finster, Kai; Hansen, Jens Würgler; Bak, Friedhelm

1993-01-01

A new chemolithotrophic bacterial metabolism was discovered in anaerobic marine enrichment cultures. Cultures in defined medium with elemental sulfur (S0) and amorphous ferric hydroxide (FeOOH) as sole substrates showed intense formation of sulfate. Furthermore, precipitation of ferrous sulfide and pyrite was observed. The transformations were accompanied by growth of slightly curved, rod-shaped bacteria. The quantification of the products revealed that S0 was microbially disproportionated to sulfate and sulfide, as follows: 4S0 + 4H2O → SO42- + 3H2S + 2H+. Subsequent chemical reactions between the formed sulfide and the added FeOOH led to the observed precipitation of iron sulfides. Sulfate and iron sulfides were also produced when FeOOH was replaced by FeCO3. Further enrichment with manganese oxide, MnO2, instead of FeOOH yielded stable cultures which formed sulfate during concomitant reduction of MnO2 to Mn2+. Growth of small rod-shaped bacteria was observed. When incubated without MnO2, the culture did not grow but produced small amounts of SO42- and H2S at a ratio of 1:3, indicating again a disproportionation of S0. The observed microbial disproportionation of S0 only proceeds significantly in the presence of sulfide-scavenging agents such as iron and manganese compounds. The population density of bacteria capable of S0 disproportionation in the presence of FeOOH or MnO2 was high, > 104 cm-3 in coastal sediments. The metabolism offers an explanation for recent observations of anaerobic sulfide oxidation to sulfate in anoxic sediments. PMID:16348835

Multidimensional MnO2 nanohair-decorated hybrid multichannel carbon nanofiber as an electrode material for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Jun, Jaemoon; Lee, Jun Seop; Shin, Dong Hoon; Kim, Sung Gun; Jang, Jyongsik

2015-09-01

One-dimensional (1D)-structured nanomaterials represent one of the most attractive candidates for energy-storage systems due to their contribution to design simplicity, fast charge-transportation network, and their allowance for more accessible ion diffusion. In particular, 1D-structured nanomaterials with a highly complex inner-pore configuration enhance functionality by taking advantage of both the hollow and 1D structures. In this study, we report a MnO2 nanohair-decorated, hybrid multichannel carbon nanofiber (Mn_MCNF) fabricated via single-nozzle co-electrospinning of two immiscible polymer solutions, followed by carbonization and redox reactions. With improved ion accessibility, the optimized Mn_MCNF sample (Mn_MCNF_60 corresponding to a reaction duration time of 60 min for optimal MnO2 nanohair growth) exhibited a high specific capacitance of 855 F g-1 and excellent cycling performance with ~87.3% capacitance retention over 5000 cycles.One-dimensional (1D)-structured nanomaterials represent one of the most attractive candidates for energy-storage systems due to their contribution to design simplicity, fast charge-transportation network, and their allowance for more accessible ion diffusion. In particular, 1D-structured nanomaterials with a highly complex inner-pore configuration enhance functionality by taking advantage of both the hollow and 1D structures. In this study, we report a MnO2 nanohair-decorated, hybrid multichannel carbon nanofiber (Mn_MCNF) fabricated via single-nozzle co-electrospinning of two immiscible polymer solutions, followed by carbonization and redox reactions. With improved ion accessibility, the optimized Mn_MCNF sample (Mn_MCNF_60 corresponding to a reaction duration time of 60 min for optimal MnO2 nanohair growth) exhibited a high specific capacitance of 855 F g-1 and excellent cycling performance with ~87.3% capacitance retention over 5000 cycles. Electronic supplementary information (ESI) available: Experimental data includes

Enhanced Sintering of β"-Al2O3/YSZ with the Sintering Aids of TiO2 and MnO2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Xiaochuan; Li, Guosheng; Kim, Jin Yong

2015-07-11

β"-Al2O3 has been the dominated choice for the electrolyte materials of sodium batteries because of its high ionic conductivity, excellent stability with the electrode materials, satisfactory mechanical strength, and low material cost. To achieve adequate electrical and mechanical performance, sintering of β"-Al2O3 is typically carried out at temperatures above 1600oC with deliberate efforts on controlling the phase, composition, and microstructure. Here, we reported a simple method to fabricate β"-Al2O3/YSZ electrolyte at relatively lower temperatures. With the starting material of boehmite, single phase of β"-Al2O3 can be achieved at as low as 1200oC. It was found that TiO2 was extremely effectivemore » as a sintering aid for the densification of β"-Al2O3 and similar behavior was observed with MnO2 for YSZ. With the addition of 2 mol% TiO2 and 5 mol% MnO2, the β"-Al2O3/YSZ composite was able to be densified at as low as 1400oC with a fine microstructure and good electrical/mechanical performance. This study demonstrated a new approach of synthesis and sintering of β"-Al2O3/YSZ composite, which represented a simple and low-cost method for fabrication of high-performance β"-Al2O3/YSZ electrolyte.« less

Three-Dimensional Bi-Continuous Nanoporous Gold/Nickel Foam Supported MnO2 for High Performance Supercapacitors.

PubMed

Zhao, Jie; Zou, Xilai; Sun, Peng; Cui, Guofeng

2017-12-19

A three-dimensional bi-continuous nanoporous gold (NPG)/nickel foam is developed though the electrodeposition of a gold-tin alloy on Ni foam and subsequent chemical dealloying of tin. The newly-designed 3D metal structure is used to anchor MnO 2 nanosheets for high-performance supercapacitors. The formed ternary composite electrodes exhibit significantly-enhanced capacitance performance, rate capability, and excellent cycling stability. A specific capacitance of 442 Fg -1 is achieved at a scan rate of 5 mV s -1 and a relatively high mass loading of 865 μg cm -2 . After 2500 cycles, only a 1% decay is found at a scan rate of 50 mV s -1 . A high power density of 3513 W kg -1 and an energy density of 25.73 Wh kg -1 are realized for potential energy storage devices. The results demonstrate that the NPG/nickel foam hybrid structure significantly improves the dispersibility of MnO 2 and makes it promising for practical energy storage applications.

Electrokinesis is a microbial behavior that requires extracellular electron transport

PubMed Central

Harris, H. W.; El-Naggar, M. Y.; Bretschger, O.; Ward, M. J.; Romine, M. F.; Obraztsova, A. Y.; Nealson, K. H.

2009-01-01

We report a previously undescribed bacterial behavior termed electrokinesis. This behavior was initially observed as a dramatic increase in cell swimming speed during reduction of solid MnO2 particles by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The same behavioral response was observed when cells were exposed to small positive applied potentials at the working electrode of a microelectrochemical cell and could be tuned by adjusting the potential on the working electrode. Electrokinesis was found to be different from both chemotaxis and galvanotaxis but was absent in mutants defective in electron transport to solid metal oxides. Using in situ video microscopy and cell tracking algorithms, we have quantified the response for different strains of Shewanella and shown that the response correlates with current-generating capacity in microbial fuel cells. The electrokinetic response was only exhibited by a subpopulation of cells closest to the MnO2 particles or electrodes. In contrast, the addition of 1 mM 9,10-anthraquinone-2,6-disulfonic acid, a soluble electron shuttle, led to increases in motility in the entire population. Electrokinesis is defined as a behavioral response that requires functional extracellular electron transport and that is observed as an increase in cell swimming speeds and lengthened paths of motion that occur in the proximity of a redox active mineral surface or the working electrode of an electrochemical cell. PMID:20018675

Dissimilatory arsenate reductase activity and arsenate-respiring bacteria in bovine rumen fluid, hamster feces, and the termite hindgut

USGS Publications Warehouse

Herbel, M.J.; Switzer, Blum J.; Hoeft, S.E.; Cohen, S.M.; Arnold, L.L.; Lisak, J.; Stolz, J.F.; Oremland, R.S.

2002-01-01

Bovine rumen fluid and slurried hamster feces completely reduced millimolar levels of arsenate to arsenite upon incubation under anoxic conditions. This activity was strongly inhibited by autoclaving or aerobic conditions, and partially inhibited by tungstate or chloramphenicol. The rate of arsenate reduction was faster in feces from a population of arsenate-watered (100 ppm) hamsters compared to a control group watered without arsenate. Using radioisotope methods, arsenate reductase activity in hamster feces was also detected at very low concentrations of added arsenate (???10 ??M). Bacterial cultures were isolated from these materials, as well as from the termite hindgut, that grew using H2 as their electron donor, acetate as their carbon source, and arsenate as their respiratory electron acceptor. The three cultures aligned phylogenetically either with well-established enteric bacteria, or with an organism associated with feedlot fecal wastes. Because arsenite is transported across the gut epithelium more readily than arsenate, microbial dissimilatory reduction of arsenate in the gut may promote the body's absorption of arsenic and hence potentiate its toxicity. ?? 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Fast and stable redox reactions of MnO2/CNT hybrid electrodes for dynamically stretchable pseudocapacitors

NASA Astrophysics Data System (ADS)

Gu, Taoli; Wei, Bingqing

2015-07-01

Pseudocapacitors, which are energy storage devices that take advantage of redox reactions to store electricity, have a different charge storage mechanism compared to lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), and they could realize further gains if they were used as stretchable power sources. The realization of dynamically stretchable pseudocapacitors and understanding of the underlying fundamentals of their mechanical-electrochemical relationship have become indispensable. We report herein the electrochemical performance of dynamically stretchable pseudocapacitors using buckled MnO2/CNT hybrid electrodes. The extremely small relaxation time constant of less than 0.15 s indicates a fast redox reaction at the MnO2/CNT hybrid electrodes, securing a stable electrochemical performance for the dynamically stretchable pseudocapacitors. This finding and the fundamental understanding gained from the pseudo-capacitive behavior coupled with mechanical deformation under a dynamic stretching mode would provide guidance to further improve their overall performance including a higher power density than LIBs, a higher energy density than EDLCs, and a long-life cycling stability. Most importantly, these results will potentially accelerate the applications of stretchable pseudocapacitors for flexible and biomedical electronics.Pseudocapacitors, which are energy storage devices that take advantage of redox reactions to store electricity, have a different charge storage mechanism compared to lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs), and they could realize further gains if they were used as stretchable power sources. The realization of dynamically stretchable pseudocapacitors and understanding of the underlying fundamentals of their mechanical-electrochemical relationship have become indispensable. We report herein the electrochemical performance of dynamically stretchable pseudocapacitors using buckled MnO2/CNT hybrid

The Effect of MnO2 Content and Sintering Atmosphere on The Electrical Properties of Iron Titanium Oxide NTC Thermistors using Yarosite

NASA Astrophysics Data System (ADS)

Wiendartun; Gustaman Syarif, Dani

2017-02-01

The effect of MnO2 content and sintering atmosphere on the characteristics of Fe2TiO5 ceramics for Negative Thermal Coefficient (NTC) thermistors by using Fe2O3 derived from yarosite has been studied. The ceramics were produced by pressing a homogeneous mixture of Fe2O3, TiO2 and MnO2 (0-2.0 w/o) powders in appropriate proportions to produce Fe2TiO5 based ceramics and sintering the pressed powder at 1100-1200°C for 3 hours in air, O2 and N2 gas. Electrical characterization was done by measuring electrical resistivity of the sintered ceramics at various temperatures from 30°C to 200°C. Microstructure and structural analyses were also carried out by using an scanning electron microscope (SEM) and x-ray diffraction (XRD). The XRD data showed that the pellets crystallize in orthorhombic. The presence of second phase could not be identified from the XRD analyses. The SEM images showed that the grain size of pellet ceramics increase with increasing of MnO2 addition, and the grains size of the ceramic sintered in oxygen gas is smaller than sintered in nitrogen gas. Electrical data showed that the value of room temperature resistance (RRT) tend to decrease with respect to the increasing of MnO2 addition and the pellet ceramics sintered in oxygen gas had the largest thermistor constant (B), activation energy (Ea), sensitivity (α) and room temperature resistance (RRT), compared to the sintered in nitrogen gas. From the electrical characteristics data, it was known that the electrical characteristics of the Fe2TiO5 pellet ceramics followed the NTC characteristic. The fabricated Fe2TiO5 ceramics have thermistor constants (B = 2207-7145K). This can be applied as temperature sensor, and will fulfill the market requirement.

Role of Cr 3+ /Cr 6+ redox in chromium-substituted Li 2 MnO 3 ·LiNi 1/2 Mn 1/2 O 2 layered composite cathodes: electrochemistry and voltage fade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Eungje; Park, Joong Sun; Wu, Tianpin

2015-01-01

The substitution of chromium into the composite Li 2MnO 3·LiNi 1/2Mn 1/2O 2cathode dramatically affects the initial electrochemical activation process; however the voltage fade process during cycling persists.

Silica-Aerogel Composites Opacified with La(0.7)Sr(0.3)MnO3

NASA Technical Reports Server (NTRS)

Rhine, Wendell; Polli, Andrew; Deshpande, Kiranmayi

2009-01-01

As part of an effort to develop improved lightweight thermal-insulation tiles to withstand temperatures up to 1,000 C, silica aerogel/fused-quartz-fiber composite materials containing La0.7Sr0.3MnO3 particles as opacifiers have been investigated as potentially offering thermal conductivities lower than those of the otherwise equivalent silica-aerogel composite materials not containing La(0.7)Sr(0.3)MnO3 particles. The basic idea of incorporating opacifying particles into silica-aerogels composite to reduce infrared radiative contributions to thermal conductivities at high temperatures is not new: it has been reported in a number of previous NASA Tech Briefs articles. What is new here is the selection of La(0.7)Sr(0.3)MnO3 particles as candidate opacifiers that, in comparison with some prior opacifiers (carbon black and metal nanoparticles), are more thermally stable. The preparation of a composite material of the present type includes synthesis of the silica-aerogel component in a sol-gel process. The La(0.7)Sr(0.3)MnO3 particles, made previously in a separate process, are mixed into the sol, which is then cast onto fused-quartz-fiber batting. Then the aerogel-casting solution is poured into the mold, where it permeates the silica fiber felt. After the sol has gelled, the casting is aged and then subjected to supercritical drying to convert the gel to the final aerogel form. The separate process for making the La(0.7)Sr(0.3)MnO3 particles begins with the slow addition of corresponding proportions of La(CH3COOH)3, Mn(CH3COOH)3, and Sr(NO3)2 to a solution of H2O2 in H2O. The solution is then peptized by drop-wise addition of NH4OH to obtain a sol. Next, the sol is dried in an oven at a temperature of 120 C to obtain a glassy solid. The solid is calcined at 700 C to convert it to La(0.7)Sr(0.3)MnO3. Then La(0.7)Sr(0.3)MnO3 particles are made by ball-milling the calcined solid. The effectiveness of La(0.7)Sr(0.3)MnO3 particles as opacifiers and thermal

Perovskite-based heterostructures integrating ferromagnetic-insulating La0.1Bi0.9MnO3

NASA Astrophysics Data System (ADS)

Gajek, M.; Bibes, M.; Barthélémy, A.; Varela, M.; Fontcuberta, J.

2005-05-01

We report on the growth of thin films and heterostructures of the ferromagnetic-insulating perovskite La0.1Bi0.9MnO3. We show that the La0.1Bi0.9MnO3 perovskite grows single phased, epitaxially, and with a single out-of-plane orientation either on SrTiO3 substrates or onto strained La2/3Sr1/3MnO3 and SrRuO3 ferromagnetic-metallic buffer layers. We discuss the magnetic properties of the La0.1Bi0.9MnO3 films and heterostructures in view of their possible potential as magnetoelectric or spin-dependent tunneling devices.

Dissimilatory reduction of nitrate and nitrite in the bovine rumen: nitrous oxide production and effect of acetylene.

PubMed Central

Kaspar, H F; Tiedje, J M

1981-01-01

15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow. Ammonium was the only 15N-labeled end product of quantitative significance. Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 0.3% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced. Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced. Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide. It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat. PMID:7224631

Lithiation Mechanism of Tunnel-Structured MnO 2 Electrode Investigated by In Situ Transmission Electron Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Seung-Yong; Wu, Lijun; Poyraz, Altug S.

Manganese oxide (α-MnO 2) has been considered as a promising energy material, including as a lithium-based battery electrode candidate, due to its environmental friendliness. Thanks to its unique 1D [2 × 2] tunnel structure, α-MnO 2 can be applied to a cathode by insertion reaction and to an anode by conversion reaction in corresponding voltage ranges, in a lithium-based battery. Numerous reports have attributed its remarkable performance to its unique tunnel structure; however, the precise electrochemical reaction mechanism remains unknown. In this study, finding of the lithiation mechanism of α-MnO 2 nanowire by in situ transmission electron microscopy (TEM) ismore » reported. By elaborately modifying the existing in situ TEM experimental technique, rapid lithium-ion diffusion through the tunnels is verified. Furthermore, by tracing the full lithiation procedure, the evolution of the MnO intermediate phase and the development of the MnO and Li 2O phases with preferred orientations is demonstrated, which explains how the conversion reaction occurs in α-MnO 2 material. This study provides a comprehensive understanding of the electrochemical lithiation process and mechanism of α-MnO 2 material, in addition to the introduction of an improved in situ TEM biasing technique.« less

Lithiation Mechanism of Tunnel-Structured MnO 2 Electrode Investigated by In Situ Transmission Electron Microscopy

DOE PAGES

Lee, Seung-Yong; Wu, Lijun; Poyraz, Altug S.; ...

2017-10-06

Manganese oxide (α-MnO 2) has been considered as a promising energy material, including as a lithium-based battery electrode candidate, due to its environmental friendliness. Thanks to its unique 1D [2 × 2] tunnel structure, α-MnO 2 can be applied to a cathode by insertion reaction and to an anode by conversion reaction in corresponding voltage ranges, in a lithium-based battery. Numerous reports have attributed its remarkable performance to its unique tunnel structure; however, the precise electrochemical reaction mechanism remains unknown. In this study, finding of the lithiation mechanism of α-MnO 2 nanowire by in situ transmission electron microscopy (TEM) ismore » reported. By elaborately modifying the existing in situ TEM experimental technique, rapid lithium-ion diffusion through the tunnels is verified. Furthermore, by tracing the full lithiation procedure, the evolution of the MnO intermediate phase and the development of the MnO and Li 2O phases with preferred orientations is demonstrated, which explains how the conversion reaction occurs in α-MnO 2 material. This study provides a comprehensive understanding of the electrochemical lithiation process and mechanism of α-MnO 2 material, in addition to the introduction of an improved in situ TEM biasing technique.« less

Effect of NO2(-) on stable isotope fractionation during bacterial sulfate reduction.

PubMed

Einsiedl, Florian

2009-01-01

The effects of low NO2(-) concentrations on stable isotope fractionation during dissimilatory sulfate reduction by strain Desulfovibrio desulfuricans were investigated. Nitrite, formed as an intermediate during nitrification and denitrification processes in marine and freshwater habitats, inhibits the reduction of the sulfuroxy intermediate SO3(2-) to H2S even at low concentrations. To gain an understanding of the inhibition effect of the reduction of the sulfuroxy intermediate on stable isotope fractionation in sulfur and oxygen during bacterial sulfate reduction, nitrite was added in the form of short pulses. In the batch experiments that contained 0.02, 0.05, and 0.1 mM nitrite, sulfur enrichment factors epsilon of -12 +/- 1.6, -15 +/- 1.1, and -26 +/- 1.3 per thousand, respectively were observed. In the control experiment (no addition of nitrite) a sulfur enrichment factor epsilon of around -11 per thousand was calculated. In the experiments that contained no 18O enriched water (delta18O: -10 per thousand) and nitrite concentrations of 0.02, 0.05, and 0.1 mM, delta18O values in the remaining sulfate were fairly constant during the experiments (delta18O sulfate: approximately equal to 10 per thousand) and were similar to those obtained from the control experiment (no nitrite and no enriched water). However, in the batch experiments that contained 18O enriched water (+700 per thousand) and nitrite concentrations of 0.05 and 0.1 mM increasing delta18O values in the remaining sulfate from around 15 per thousand to approximately 65 and 85 per thousand, respectively, were found. Our experiments that contained isotopic enriched water and nitrite show clear evidence that the ratio of forward and backward fluxes regulated by adenosine-5'-phosphosulfate reductase (APSR) controls the extent of sulfur isotope fractionation during bacterial sulfate reduction in strain Desulfovibrio desulfuricans. Since the metabolic sulfuroxy intermediate SO3(2-) exchanges with water

High loading MnO2 nanowires on graphene paper: facile electrochemical synthesis and use as flexible electrode for tracking hydrogen peroxide secretion in live cells.

PubMed

Dong, Shuang; Xi, Jiangbo; Wu, Yanan; Liu, Hongwei; Fu, Chaoyang; Liu, Hongfang; Xiao, Fei

2015-01-01

Recent progress in flexible and lightweight electrochemical sensor systems requires the development of paper-like electrode materials. Here, we report a facile and green synthesis of a new type of MnO2 nanowires-graphene nanohybrid paper by one-step electrochemical method. This strategy demonstrates a collection of unique features including the effective electrochemical reduction of graphene oxide (GO) paper and the high loading of MnO2 nanowires on electrochemical reduced GO (ERGO) paper. When used as flexible electrode for nonenzymatic detection of hydrogen peroxide (H2O2), MnO2-ERGO paper exhibits high electrocatalytic activity toward the redox of H2O2 as well as excellent stability, selectivity and reproducibility. The amperometric responses are linearly proportional to H2O2 concentration in the range 0.1-45.4 mM, with a detection limit of 10 μM (S/N=3) and detection sensitivity of 59.0 μA cm(-2) mM(-1). These outstanding sensing performances enable the practical application of MnO2-ERGO paper electrode for the real-time tracking H2O2 secretion by live cells macrophages. Therefore, the proposed graphene-based nanohybrid paper electrode with intrinsic flexibility, tailorable shapes and adjustable properties can contribute to the full realization of high-performance flexible electrode material used in point-of-care testing devices and portable instruments for in-vivo clinical diagnostics and on-site environmental monitoring. Copyright © 2014 Elsevier B.V. All rights reserved.

Constructing Sheet-On-Sheet Structured Graphitic Carbon Nitride/Reduced Graphene Oxide/Layered MnO2 Ternary Nanocomposite with Outstanding Catalytic Properties on Thermal Decomposition of Ammonium Perchlorate

PubMed Central

Xu, Jianhua; Li, Dongnan; Chen, Yu; Tan, Linghua; Kou, Bo; Wan, Fushun; Jiang, Wei; Li, Fengsheng

2017-01-01

We unprecedentedly report that layered MnO2 nanosheets were in situ formed onto the surface of covalently bonded graphitic carbon nitride/reduced graphene oxide nanocomposite (g-C3N4/rGO), forming sheet-on-sheet structured two dimension (2D) graphitic carbon nitride/reduced graphene oxide/layered MnO2 ternary nanocomposite (g-C3N4/rGO/MnO2) with outstanding catalytic properties on thermal decomposition of ammonium perchlorate (AP). The covalently bonded g-C3N4/rGO was firstly prepared by the calcination of graphene oxide-guanidine hydrochloride precursor (GO-GndCl), following by its dispersion into the KMnO4 aqueous solution to construct the g-C3N4/rGO/MnO2 ternary nanocomposite. FT-IR, XRD, Raman as well as the XPS results clearly demonstrated the chemical interaction between g-C3N4, rGO and MnO2. TEM and element mapping indicated that layered g-C3N4/rGO was covered with thin MnO2 nanosheets. Furthermore, the obtained g-C3N4/rGO/MnO2 nanocomposite exhibited promising catalytic capacity on thermal decomposition of AP. Upon addition of 2 wt % g-C3N4/rGO/MnO2 ternary nanocomposite as catalyst, the thermal decomposition temperature of AP was largely decreased up by 142.5 °C, which was higher than that of pure g-C3N4, g-C3N4/rGO and MnO2, respectively, demonstrating the synergistic catalysis of the as-prepared nanocomposite. PMID:29244721

The design of an Fe-12Mn-O.2Ti alloy steel for low temperature use

NASA Technical Reports Server (NTRS)

Hwang, S. K.; Morris, J. W., Jr.

1977-01-01

An investigation was made to improve the low temperature mechanical properties of Fe-8 approximately 12% Mn-O 2Ti alloy steels. A two-phase(alpha + gamma) tempering in combination with cold working or hot working was identified as an effective treatment. A potential application as a Ni-free cryogenic steel was shown for this alloy. It was also shown that an Fe-8Mn steel could be grain-refined by a purely thermal treatment because of its dislocated martensitic structure and absence of epsilon phase. A significant reduction of the ductile-brittle transition temperature was obtained in this alloy. The nature and origin of brittle fracture in Fe-Mn alloys were also investigated. Two embrittling regions were found in a cooling curve of an Fe-12Mn-O 2Ti steel which was shown to be responsible for intergranular fracture. Auger electron spectroscopy identified no segregation during solution-annealing treatment. Avoiding the embrittling zones by controlled cooling led to a high cryogenic toughness in a solution-annealed condition.

Floating zone growth of α-Na 0.90MnO 2 single crystals

DOE PAGES

Dally, Rebecca; Clement, Raphaele J.; Chisnell, Robin; ...

2016-12-03

Here, single crystal growth of α-Na xMnO 2 (x=0.90) is reported via the floating zone technique. The conditions required for stable growth and intergrowth-free crystals are described along with the results of trials under alternate growth atmospheres. Chemical and structural characterizations of the resulting α-Na 0.90MnO 2 crystals are performed using ICP-AES NMR, XANES, XPS, and neutron diffraction measurements. As a layered transition metal oxide with large ionic mobility and strong correlation effects, α-Na xMnO 2 is of interest to many communities, and the implications of large volume, high purity, single crystal growth are discussed.

Symmetric Sodium-Ion Capacitor Based on Na0.44MnO2 Nanorods for Low-Cost and High-Performance Energy Storage.

PubMed

Chen, Zhongxue; Yuan, Tianci; Pu, Xiangjun; Yang, Hanxi; Ai, Xinping; Xia, Yongyao; Cao, Yuliang

2018-04-11

Batteries and electrochemical capacitors play very important roles in the portable electronic devices and electric vehicles and have shown promising potential for large-scale energy storage applications. However, batteries or capacitors alone cannot meet the energy and power density requirements because rechargeable batteries have a poor power property, whereas supercapacitors offer limited capacity. Here, a novel symmetric sodium-ion capacitor (NIC) is developed based on low-cost Na 0.44 MnO 2 nanorods. The Na 0.44 MnO 2 with unique nanoarchitectures and iso-oriented feature offers shortened diffusion path lengths for both electronic and Na + transport and reduces the stress associated with Na + insertion and extraction. Benefiting from these merits, the symmetric device achieves a high power density of 2432.7 W kg -1 , an improved energy density of 27.9 Wh kg -1 , and a capacitance retention of 85.2% over 5000 cycles. Particularly, the symmetric NIC based on Na 0.44 MnO 2 permits repeatedly reverse-polarity characteristics, thus simplifying energy management system and greatly enhancing the safety under abuse condition. This cost-effective, high-safety, and high-performance symmetric NIC can balance the energy and power density between batteries and capacitors and serve as an electric power source for future low-maintenance large-scale energy storage systems.

Synthesis of vertical MnO2 wire arrays on hemp-derived carbon for efficient and robust green catalysts

NASA Astrophysics Data System (ADS)

Yang, MinHo; Kim, Dong Seok; Sim, Jae-Wook; Jeong, Jae-Min; Kim, Do Hyun; Choi, Jae Hyung; Kim, Jinsoo; Kim, Seung-Soo; Choi, Bong Gill

2017-06-01

Three-dimensional (3D) carbon materials derived from waste biomass have been attracted increasing attention in catalysis and materials science because of their great potential of catalyst supports with respect to multi-functionality, unique structures, high surface area, and low cost. Here, we present a facile and efficient way for preparing 3D heterogeneous catalysts based on vertical MnO2 wires deposited on hemp-derived 3D porous carbon. The 3D porous carbon materials are fabricated by carbonization and activation processes using hemp (Cannabis Sttiva L.). These 3D porous carbon materials are employed as catalyst supports for direct deposition of vertical MnO2 wires using a one-step hydrothermal method. The XRD and XPS results reveal the crystalline structure of α-MnO2 wires. The resultant composites are further employed as a catalyst for glycolysis of poly(ethylene terephthalate) (PET) with high conversion yield of 98%, which is expected to be expressly profitable for plastics recycling industry.

Pyrite discs in coal: evidence for fossilized bacterial colonies

USGS Publications Warehouse

Southam, G.; Donald, R.; Rostad, A.; Brock, C.

2001-01-01

Discs of pyrite from 1 to 3 mm in diameter and ∼100 μm thick were observed within fracture planes in coal from the Black Mesa coal deposit in northeastern Arizona. The pyrite discs were composed of aggregates of crystals, which suggested that sulfide mineral diagenesis had initiated at multiple nucleation sites and occurred prior to the compaction forces occurring during coal formation. Stable sulfur isotope analysis of the discs (δ34S = −31.7‰) supports a bacterial origin resulting from dissimilatory sulfate reduction. Fossilized bacteria on the disc surfaces (average = 27/100 μm2) appeared as halos when viewed using reflected light microscopy, but were lenticular by scanning electron microscopy, each microfossil being 2–3 μm in length. A fossilized bacterial colony (pyrite disc), 1 mm in diameter, would contain ∼2.1 × 107 microfossils. These microfossils were not observed on hydrothermal pyrite. Coating and in-filling of sulfate-reducing bacteria with iron disulfide during in vitro sulfide mineral diagenesis provide mechanisms to explain the preservation of the three-dimensional lenticular microfossils observed on the pyrite discs.

Development of 3D Urchin-Shaped Coaxial Manganese Dioxide@Polyaniline (MnO2@PANI) Composite and Self-Assembled 3D Pillared Graphene Foam for Asymmetric All-Solid-State Flexible Supercapacitor Application.

PubMed

Ghosh, Kalyan; Yue, Chee Yoon; Sk, Md Moniruzzaman; Jena, Rajeeb Kumar

2017-05-10

We have fabricated high-energy-density all-solid-state flexible asymmetric supercapacitor by using a facile novel 3D hollow urchin-shaped coaxial manganese dioxide@polyaniline (MnO 2 @PANI) composite as positive electrode and 3D graphene foam (GF) as negative electrode materials with polyvinyl alcohol (PVA)/KOH gel electrolyte. The coaxial MnO 2 @PANI composite was fabricated by hydrothermal route followed by oxidation without use of an external oxidant. The formation mechanism of the 3D hollow MnO 2 @PANI composite occurs first by nucleation and growth of the MnO 2 crystal species via dissolution-recrystallization and oriented attachment mechanisms followed by the oxidation of aniline monomers on the MnO 2 crystalline template. The self-assembled 3D graphene block was synthesized by hydrothermal route using vitamin C as a reducing agent. The microstructures of the composites are analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The morphology is characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), which clearly showed the formation of urchin-shaped coaxial MnO 2 @PANI composite. The electrochemical studies are explored by cyclic voltammetry, electrochemical impedance spectrometry, and cyclic charge-discharge tests. The symmetric all-solid-state flexible MnO 2 @PANI//MnO 2 @PANI and GF//GF supercapacitors exhibit the specific capacitance of 129.2 and 82.1 F g -1 at 0.5 A/g current density, respectively. The solid-state asymmetric supercapacitor shows higher energy density (37 Wh kg -1 ) with respect to the solid-state symmetric supercapacitors MnO 2 @PANI//MnO 2 @PANI and GF//GF, where the obtained energy density are found to be 17.9 and 11.4 Wh kg -1 , respectively, at 0.5 A/g current density. Surprisingly, the asymmetric supercapacitor shows a high energy density of 22.3 Wh kg -1 at a high current density of 5 A g -1 . The solid-state asymmetric

Effects of cooling interval and MnO2, TiO2, CdO, NiO additions on spheluritic willemite crystals

NASA Astrophysics Data System (ADS)

Coşkun, Nihal Derin; Uz, Veli; Issi, Ali; Genç, Soner; Çakı, Münevver

2017-01-01

Macro crystal production in crystal glaze systems is a very important topic in ceramic art and science. In this study, crystal growth was obtained in two different firing regimes. Recipes were prepared by adding MnO, TiO, NiO and CdO into the frit. The first firing regime, which is used in artistic ceramics, has a 100 °C cooling temperature interval. The second regime that has a 580 °C cooling temperature interval, was determined by DTA analysis. Then, the development of crystals was compared between these two firing regimes. According to the results, spheluritic willemite crystals up to three cm in the glazes doped MnO2 have been obtained by cooling it in a wide cooling interval. Larger willemite crystals were not formed in the narrow cooling temperature interval. It was determined that larger crystals can be produced by cooling at wide cooling temperature intervals and holding at lower temperature which involves nucleating the temperature of the crystal.

Polydopamine and MnO2 core-shell composites for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Hou, Ding; Tao, Haisheng; Zhu, Xuezhen; Li, Maoguo

2017-10-01

Polydopamine and MnO2 core-shell composites (PDA@MnO2) for high-performance supercapacitors had been successfully synthesized by a facile and fast method. The morphology, crystalline phase and chemical composition of PDA@MnO2 composites are characterized using SEM, TEM, XRD, EDS and XPS. The performance of PDA@MnO2 composites are further investigated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy in 1 M Na2SO4 electrolyte. The PDA@MnO2 core-shell nanostructure composites exhibit a high capacitance of 193 F g-1 at the current density of 1A g-1 and retained over 81.2% of its initial capacitance after 2500 cycles of charge-discharge at 2 A g-1. The results manifest that the PDA@MnO2 composites can be potentially applied in supercapacitors.

A-site cationic disorder induced significantly large magnetoresistance in polycrystalline La0.2Gd0.5Ba0.3MnO3 compound

NASA Astrophysics Data System (ADS)

Saha, Suvayan; Das, Kalipada; Bandyopadhyay, Sudipta; Das, I.

2017-11-01

The observation of significantly large magnetoresistance at the liquid nitrogen temperature range in the polycrystalline La0.2Gd0.5Ba0.3MnO3 (LGBMO) compound has been addressed in the present manuscript. The motivation of considering LGBMO sample is the average 'A' site ionic radius 〈rA 〉 and tolerance factor (t), almost same as that of La0.7Sr0.3MnO3 (LSMO), which is a well studied colossal magnetoresistive material. Magnetoresistance of the LGBMO compound has been compared with the LSMO as well as parent compound La0.7Ba0.3MnO3(LBMO) to show the enhancement of magnetoresistance in LGBMO compound. This observed nature has been elucidated considering the disorder induced short range magnetic interaction due to the enhance size disorder parameter (σ2). Our study revels that, size disorder parameter plays the crucial role for enhancing the colossal magnetoresistance.

Multidimensional MnO2 nanohair-decorated hybrid multichannel carbon nanofiber as an electrode material for high-performance supercapacitors.

PubMed

Jun, Jaemoon; Lee, Jun Seop; Shin, Dong Hoon; Kim, Sung Gun; Jang, Jyongsik

2015-10-14

One-dimensional (1D)-structured nanomaterials represent one of the most attractive candidates for energy-storage systems due to their contribution to design simplicity, fast charge-transportation network, and their allowance for more accessible ion diffusion. In particular, 1D-structured nanomaterials with a highly complex inner-pore configuration enhance functionality by taking advantage of both the hollow and 1D structures. In this study, we report a MnO2 nanohair-decorated, hybrid multichannel carbon nanofiber (Mn_MCNF) fabricated via single-nozzle co-electrospinning of two immiscible polymer solutions, followed by carbonization and redox reactions. With improved ion accessibility, the optimized Mn_MCNF sample (Mn_MCNF_60 corresponding to a reaction duration time of 60 min for optimal MnO2 nanohair growth) exhibited a high specific capacitance of 855 F g(-1) and excellent cycling performance with ∼87.3% capacitance retention over 5000 cycles.

Dissolution of Arsenic Minerals Mediated by Dissimilatory Arsenate Reducing Bacteria: Estimation of the Physiological Potential for Arsenic Mobilization

PubMed Central

Lukasz, Drewniak; Liwia, Rajpert; Aleksandra, Mantur; Aleksandra, Sklodowska

2014-01-01

The aim of this study was characterization of the isolated dissimilatory arsenate reducing bacteria in the context of their potential for arsenic removal from primary arsenic minerals through reductive dissolution. Four strains, Shewanella sp. OM1, Pseudomonas sp. OM2, Aeromonas sp. OM4, and Serratia sp. OM17, capable of anaerobic growth with As (V) reduction, were isolated from microbial mats from an ancient gold mine. All of the isolated strains: (i) produced siderophores that promote dissolution of minerals, (ii) were resistant to dissolved arsenic compounds, (iii) were able to use the dissolved arsenates as the terminal electron acceptor, and (iii) were able to use copper minerals containing arsenic minerals (e.g., enargite) as a respiratory substrate. Based on the results obtained in this study, we postulate that arsenic can be released from some As-bearing polymetallic minerals (such as copper ore concentrates or middlings) under reductive conditions by dissimilatory arsenate reducers in indirect processes. PMID:24724102

Dissolution of arsenic minerals mediated by dissimilatory arsenate reducing bacteria: estimation of the physiological potential for arsenic mobilization.

PubMed

Lukasz, Drewniak; Liwia, Rajpert; Aleksandra, Mantur; Aleksandra, Sklodowska

2014-01-01

The aim of this study was characterization of the isolated dissimilatory arsenate reducing bacteria in the context of their potential for arsenic removal from primary arsenic minerals through reductive dissolution. Four strains, Shewanella sp. OM1, Pseudomonas sp. OM2, Aeromonas sp. OM4, and Serratia sp. OM17, capable of anaerobic growth with As (V) reduction, were isolated from microbial mats from an ancient gold mine. All of the isolated strains: (i) produced siderophores that promote dissolution of minerals, (ii) were resistant to dissolved arsenic compounds, (iii) were able to use the dissolved arsenates as the terminal electron acceptor, and (iii) were able to use copper minerals containing arsenic minerals (e.g., enargite) as a respiratory substrate. Based on the results obtained in this study, we postulate that arsenic can be released from some As-bearing polymetallic minerals (such as copper ore concentrates or middlings) under reductive conditions by dissimilatory arsenate reducers in indirect processes.

Application of biomass-derived flexible carbon cloth coated with MnO2 nanosheets in supercapacitors

NASA Astrophysics Data System (ADS)

He, Shuijian; Chen, Wei

2015-10-01

Successful application of inexpensive energy storage devices lies in the exploitation of fabrication approaches that are based on cost-efficient materials and that can be easily scaled up. Here, inexpensive textile weaved by natural flax fiber is selected as raw material in preparing flexible and binder-free electrode material for supercapacitors. Although carbon fiber cloth obtained from the direct carbonization of flax textile exhibits a low specific capacitance of 0.78 F g-1, carbon fiber cloth electrode shows a very short relaxation time of 39.1 m s and good stability with almost 100% capacitance retaining after 104 cycles at 5 A g-1. To extend the application of the resulting carbon cloth in supercapacitor field, a layer of MnO2 nanosheets is deposited on the surface of carbon fiber via in situ redox reaction between carbon and KMnO4. The specific capacitance of MnO2 reaches 683.73 F g-1 at 2 A g-1 and still retains 269.04 F g-1 at 300 A g-1, indicating the excellent rate capacitance performance of the carbon cloth/MnO2 hybrids. The present study shows that carbon cloth derived from flax textile can provide a low-cost material platform for the facile, cost-efficient and large scale fabrication of binder-free electrode materials for energy storage devices.

Green Synthesis of Three-Dimensional MnO2/Graphene Hydrogel Composites as a High-Performance Electrode Material for Supercapacitors.

PubMed

Meng, Xiaoyi; Lu, Liang; Sun, Chunwen

2018-05-16

Graphene hydrogels (GHs) and their composites have attracted wide attention because of the special structure of graphene assembly and exceptional electrochemical performance as electrodes for energy storage devices. Here, we report a GH with three-dimensional architecture prepared by a hydrothermal method via a self-assembled process in glucose and ammonia system as well as subsequent freeze-drying. The δ-MnO 2 /GH composite was then obtained by immersing GH in KMnO 4 solution with a certain concentration under heat treatment. The asymmetric supercapacitor MnO 2 /GH//GH consisting of pseudocapacitive nanosheet-like δ-MnO 2 /GH as the cathode and electric double-layer capacitive GH as the anode provides high energy density of 34.7 W h/kg at a power density of 1.0 kW/kg. Importantly, it is found that the pseudocapacitive behavior of MnO 2 has great effects on the rate performance of the supercapacitor, which is identified by kinetic analysis.

Seasonal variation in denitrification and dissimilatory nitrate reduction to ammonia process rates and corresponding key functional genes along an estuarine nitrate gradient

PubMed Central

Smith, Cindy J.; Dong, Liang F.; Wilson, John; Stott, Andrew; Osborn, A. Mark; Nedwell, David B.

2015-01-01

This research investigated spatial-temporal variation in benthic bacterial community structure, rates of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) processes and abundances of corresponding genes and transcripts at three sites—the estuary-head, mid-estuary and the estuary mouth (EM) along the nitrate gradient of the Colne estuary over an annual cycle. Denitrification rates declined down the estuary, while DNRA rates were higher at the estuary head and middle than the EM. In four out of the six 2-monthly time-points, rates of DNRA were greater than denitrification at each site. Abundance of gene markers for nitrate-reduction (nitrate reductase narG and napA), denitrification (nitrite reductase nirS) and DNRA (DNRA nitrite reductase nrfA) declined along the estuary with significant relationships between denitrification and nirS abundance, and DNRA and nrfA abundance. Spatially, rates of denitrification, DNRA and corresponding functional gene abundances decreased along the estuary. However, temporal correlations between rate processes and functional gene and transcript abundances were not observed. PMID:26082763

Immobilization of R-ω-transaminase on MnO2 nanorods for catalyzing the conversion of (R)-1-phenylethylamine.

PubMed

Sun, Jian; Cui, Wen-Hui; Du, Kun; Gao, Qian; Du, Mengmeng; Ji, Peijun; Feng, Wei

2017-03-10

R-ɷ-transaminases transfer an amino group from an amino donor (e.g. (R)-1-phenylethylamine) onto an amino acceptor (e.g. pyruvate), resulting a co-product (e.g. d-alanine). This work intends to immobilize R-ɷ-Transaminase on MnO 2 nanorods to achieve multienzyme catalysis. R-ɷ-Transaminase (RTA) and d-amino acid oxidase (DAAO) have been fused to an elastin-like polypeptide (ELP) separately through genetic engineering of the enzymes. ELP-RTA and ELP-DAAO have been separately immobilized on polydopamine-coated MnO 2 nanorods. When the two immobilized enzymes were used together in one pot, the transformation of (R)-1-phenylethylamine was catalyzed by the immobilized ELP-RTA, and the co-product d-alanine was converted back to pyruvate under the catalysis of the immobilized ELP-DAAO, achieving the recycling of pyruvate in situ. Thus pyruvate was maintained at a low concentration in order to reduce its negative effect. On the other hand, the generated H 2 O 2 of ELP-DAAO was decomposed by the MnO 2 nanorods, and the evolved oxygen oxidized the reduced cofactors of ELP-DAAO. Forming the circles of hydrogen peroxide→oxygen→hydrogen peroxide accelerated the deamination reaction. The highly efficient conversion of the co-product d-alanine back to pyruvate accelerated the forming of the pyruvate→d-alanine→pyruvate cycle between the two immobilized enzymes. The coordination of the pyruvate→d-alanine→pyruvate and hydrogen peroxide→oxygen→hydrogen peroxide cycles accelerated the transformation of (R)-1-phenylethylamine. As a result, As a result, the immobilized enzymes achieved a conversion of 98±1.8% in comparison to 69.6±1.2% by free enzymes. Copyright © 2017 Elsevier B.V. All rights reserved.

Doping Li-rich cathode material Li2MnO3 : Interplay between lattice site preference, electronic structure, and delithiation mechanism

NASA Astrophysics Data System (ADS)

Hoang, Khang

2017-12-01

We report a detailed first-principles study of doping in Li2MnO3 , in both the dilute doping limit and heavy doping, using hybrid density-functional calculations. We find that Al, Fe, Mo, and Ru impurities are energetically most favorable when incorporated into Li2MnO3 at the Mn site, whereas Mg is most favorable when doped at the Li sites. Nickel, on the other hand, can be incorporated at the Li site and/or the Mn site, and the distribution of Ni over the lattice sites can be tuned by tuning the material preparation conditions. There is a strong interplay among the lattice site preference and charge and spin states of the dopant, the electronic structure of the doped material, and the delithiation mechanism. The calculated electronic structure and voltage profile indicate that in Ni-, Mo-, or Ru-doped Li2MnO3 , oxidation occurs on the electrochemically active transition-metal ion(s) before it does on oxygen during the delithiation process. The role of the dopants is to provide charge compensation and bulk electronic conduction mechanisms in the initial stages of delithiation, hence enabling the oxidation of the lattice oxygen in the later stages. This work thus illustrates how the oxygen-oxidation mechanism can be used in combination with the conventional mechanism involving transition-metal cations in design of high-capacity battery cathode materials.

Anomalous magnetic behavior of Sm0.8Ca0.2MnO3 nanoparticles.

PubMed

Mogilyansky, D; Fita, I; Wisniewski, A; Markovich, V; Puzniak, R; Gorodetsky, G

2012-11-01

Magnetic properties of compacted Sm0.8Ca0.2MnO3 (SCMO) particles with average particle size of 23-100 nm, prepared by the glycine-nitrate method, have been investigated. It was found that the relative volume of the ferromagnetic phase decreases with decreasing particle size. Curves of field cooled and zero filed cooled magnetization (M(ZFC)) exhibit a bifurcation just below the Curie temperature (T(c) approximately 55-64 K) for all particles studied. The field dependence of M(ZFC) peak follows de Almeida-Thouless line. Both features are characteristic of spin-glasses (SG). Measurements of ac-susceptibility in the temperature range 5-300 K and the frequency range f = 10 Hz-10 kHz show a sharp peak for both real and imaginary components in the vicinity of T(c), apparently attributed to the Hopkinson effect. A second small peak is seemingly associated with antiferromagnetic or ferrimagnetic ordering. Though, for smaller particles both peaks depend on frequency, no shift to higher temperatures with increasing f, characteristic for SG systems, was observed. The dissimilarity in magnetic properties and dynamic characteristics observed for SCMO and for La0.8Ca0.2MnO3 nanoparticles is discussed, taking into account a difference in the width of the band and the strength of double exchange and interparticle interactions.

Predicting heavy metals' adsorption edges and adsorption isotherms on MnO2 with the parameters determined from Langmuir kinetics.

PubMed

Hu, Qinghai; Xiao, Zhongjin; Xiong, Xinmei; Zhou, Gongming; Guan, Xiaohong

2015-01-01

Although surface complexation models have been widely used to describe the adsorption of heavy metals, few studies have verified the feasibility of modeling the adsorption kinetics, edge, and isotherm data with one pH-independent parameter. A close inspection of the derivation process of Langmuir isotherm revealed that the equilibrium constant derived from the Langmuir kinetic model, KS-kinetic, is theoretically equivalent to the adsorption constant in Langmuir isotherm, KS-Langmuir. The modified Langmuir kinetic model (MLK model) and modified Langmuir isotherm model (MLI model) incorporating pH factor were developed. The MLK model was employed to simulate the adsorption kinetics of Cu(II), Co(II), Cd(II), Zn(II) and Ni(II) on MnO2 at pH3.2 or 3.3 to get the values of KS-kinetic. The adsorption edges of heavy metals could be modeled with the modified metal partitioning model (MMP model), and the values of KS-Langmuir were obtained. The values of KS-kinetic and KS-Langmuir are very close to each other, validating that the constants obtained by these two methods are basically the same. The MMP model with KS-kinetic constants could predict the adsorption edges of heavy metals on MnO2 very well at different adsorbent/adsorbate concentrations. Moreover, the adsorption isotherms of heavy metals on MnO2 at various pH levels could be predicted reasonably well by the MLI model with the KS-kinetic constants. Copyright © 2014. Published by Elsevier B.V.

Dissimilatory perchlorate reduction: a review.

PubMed

Bardiya, Nirmala; Bae, Jae-Ho

2011-05-20

In the United States anthropogenic activities are mainly responsible for the wide spread perchlorate contamination of drinking water, surface water, groundwater, and soil. Even at microgram levels, perchlorate causes toxicity to flora and fauna and affects growth, metabolism and reproduction in humans and animals. Reports of antithyroid effects of perchlorate and its detection in common food items have raised serious public health concerns, leading to extensive decontamination efforts in recent years. Several physico-chemical removal and biological decontamination processes are being developed. Although promising, ion exchange is a non-selective and incomplete process as it merely transfers perchlorate from water to the resin. The perchlorate-laden spent resins (perchlorate 200-500 mg L(-1)) require regeneration resulting in production of concentrated brine (6-12% NaCl) or caustic waste streams. On the contrary, biological reduction completely degrades perchlorate into O(2) and innocuous Cl(-). High reduction potential of ClO(4)(-)/Cl(-) (E° =∼ 1.28 V) and ClO(3)(-)/Cl(-) pairs (E° =1.03 V) makes these contaminants thermodynamically ideal e(-) acceptors for microbial reduction. In recent years unique dissimilatory perchlorate reducing bacteria have been isolated and detailed studies pertaining to their microbiological, biochemical, genetics and phylogenetic aspects have been undertaken which is the subject of this review article while the various physico-chemical removal and biological reduction processes have been reviewed by others. Copyright © 2010 Elsevier GmbH. All rights reserved.

H-TiO(2) @MnO(2) //H-TiO(2) @C core-shell nanowires for high performance and flexible asymmetric supercapacitors.

PubMed

Lu, Xihong; Yu, Minghao; Wang, Gongming; Zhai, Teng; Xie, Shilei; Ling, Yichuan; Tong, Yexiang; Li, Yat

2013-01-11

A flexible solid-state asymmetric supercapacitor device with H-TiO(2) @MnO(2) core-shell NWs as the positive electrode and H-TiO(2) @C core-shell NWs as the negative electrode is developed. This device operates in a 1.8 V voltage window and is able to deliver a high specific capacitance of 139.6 F g(-1) and maximum volumetric energy density of 0.30 mWh cm(-3) with excellent cycling performance and good flexibility. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A new concept for high-cycle-life LEO: Rechargeable MnO2-hydrogen

NASA Technical Reports Server (NTRS)

Appleby, A. John; Dhar, Y. J.; Murphy, O. J.; Srinivasan, Supramaniam

1989-01-01

The nickel-hydrogen secondary battery system is now the one of choice for use in GEO satellites. It offers superior energy density to that of nickel-cadmium, with a lifetime that is at least comparable in terms of both cycle life and overall operating life. While the number of deep cycles required for GEO use is small, LEO satellites with long lifetimes (5 to 10 years) will require secondary battery systems allowing 30,000 to 60,000 useful cycles which are characterized by an approximately 2C charge rate and C average discharge rate. Recent work has shown that birnessite MnO2 doped with bismuth oxide can be cycled at very high rates (6C) over a very large number of cycles (thousands) at depths-of-discharge in the 85 to 90 percent range, based on two electrons, which discharge at the same potential in a flat plateau. The potential is about 0.7 V vs. hydrogen, with a cut-off at 0.6 V. At first sight, this low voltage would seem to be a disadvantage, since the theoretical energy density will be low. However, it permits the use of lightweight materials that are immune from corrosion at the positive. The high utilization and low equivalent weight of the active material, together with the use of teflon-bonded graphite for current collection, result in very light positives, especially when these are compared with those in a derated nickel-hydrogen system. In addition, the weight of the pressure vessel falls somewhat, since the dead volume is lower. Calculations show that a total system will have 2.5 times the Ah capacity of a derated nickel-hydrogen LEO battery, so that the energy density, based on 1.2 V for nickel-hydrogen and 0.7 V for MnO2-hydrogen, will be 45 percent higher for comparable cycling performance.

The effect of bismuth on the structure, magnetic and electric properties of Co2MnO4 spinel multiferroic

NASA Astrophysics Data System (ADS)

Chouaya, H.; Smari, M.; Walha, I.; Dhahri, E.; Graça, M. P. F.; Valente, M. A.

2018-04-01

Mixed Co2Mn1-xBixO4 (x = 0, x = 0.05 and x = 0.1) samples were prepared by the sol-gel method using the citric acid route and characterized by various techniques. The X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure with Fd 3 ‾ m space group. The introduction of Bismuth (Bi) into Co2MnO4 did not modify the ferrimagnetic character of the parent compound Co2MnO4, whereas the field-cooled magnetizations MFC and the Curie temperature Tc decreased when increasing the Bi content. The electrical properties showed an activation energy (Ea) increase caused by the decrease of the double-exchange interaction following the substitution of Mn3+ by Bi3+. Eventually, the temperature coefficient of resistance (TCR) shows significant values for all samples can be investigated also as good candidates for bolometer applications.

Stoichiometric modelling of assimilatory and dissimilatory biomass utilisation in a microbial community

PubMed Central

Hunt, Kristopher A.; Jennings, Ryan deM.; Inskeep, William P.; Carlson, Ross P.

2017-01-01

Summary Assimilatory and dissimilatory utilisation of autotroph biomass by heterotrophs is a fundamental mechanism for the transfer of nutrients and energy across trophic levels. Metagenome data from a tractable, thermoacidophilic microbial community in Yellowstone National Park was used to build an in silico model to study heterotrophic utilisation of autotroph biomass using elementary flux mode analysis and flux balance analysis. Assimilatory and dissimilatory biomass utilisation was investigated using 29 forms of biomass-derived dissolved organic carbon (DOC) including individual monomer pools, individual macromolecular pools and aggregate biomass. The simulations identified ecologically competitive strategies for utilizing DOC under conditions of varying electron donor, electron acceptor or enzyme limitation. The simulated growth environment affected which form of DOC was the most competitive use of nutrients; for instance, oxygen limitation favoured utilisation of less reduced and fermentable DOC while carbon-limited environments favoured more reduced DOC. Additionally, metabolism was studied considering two encompassing metabolic strategies: simultaneous versus sequential use of DOC. Results of this study bound the transfer of nutrients and energy through microbial food webs, providing a quantitative foundation relevant to most microbial ecosystems. PMID:27387069

The influences of shape and structure of MnO2 nanomaterials over the non-enzymatic sensing ability of hydrogen peroxide

NASA Astrophysics Data System (ADS)

Babu, K. Justice; Zahoor, Awan; Nahm, Kee Suk; Ramachandran, R.; Rajan, M. A. Jothi; Gnana kumar, G.

2014-02-01

The different morphologies of MnO2 nanomaterials such as rod, belt, and flower were synthesized through a facile hydrothermal method, and their phases were also effectively controlled without employing any organic surfactants. The growth mechanisms of prepared nanostructures has been rationalized through the observed morphologic and structural characterizations. The prepared MnO2 nanostructures improved the electron transfer kinetics and minimized the overpotential and exhibited good electrocatalytic activities in detecting the hydrogen peroxide. Among the studied nanostructures, r-MnO2 exhibited an excellent sensing behavior toward hydrogen peroxide, and a linear current response was observed for the hydrogen peroxide, ranging from 1 micromolar to 1.5 mM with a high-sensitivity and low-level detection limit of 62.9 μAmM-1 cm-2 and 0.1 μM, respectively. Moreover, r-MnO2-modified electrode exhibited high selectivity toward hydrogen peroxide and interference-free phenomenon for the other electroactive species.

Magnetic-field-dependent dielectric constant in La2/3Ca1/3MnO3

NASA Astrophysics Data System (ADS)

Rivas, J.; Mira, J.; Rivas-Murias, B.; Fondado, A.; Dec, J.; Kleemann, W.; Señarís-Rodríguez, M. A.

2006-06-01

We report a rather high dependence of the dielectric permittivity on the magnetic field in La2/3Ca1/3MnO3. The variation is maximum at around 270K, little above the Curie temperature TC, and it reaches a 35% under only 0.5T. We attribute this phenomenon to the space-charge or interfacial polarization produced between the insulator and the metallic regions segregated intrinsically in the material above TC.

Nanostructured MnO2-Based Cathodes for Li-Ion/Polymer Cells

NASA Technical Reports Server (NTRS)

Skandan, Ganesh; Singhal, Amit

2005-01-01

Nanostructured MnO2-based cathodes for Li-ion/polymer electrochemical cells have been investigated in a continuing effort to develop safe, high-energy-density, reliable, low-toxicity, rechargeable batteries for a variety of applications in NASA programs and in mass-produced commercial electronic equipment. Whereas the energy densities of state-of-the-art lithium-ion/polymer batteries range from 150 to 175 W h/kg, the goal of this effort is to increase the typical energy density to about 250 W h/kg. It is also expected that an incidental benefit of this effort will be increases in power densities because the distances over which Li ions must diffuse through nanostructured cathode materials are smaller than those through solid bulk cathode materials.

The electrochemical performance of aqueous rechargeable battery of Zn/Na0.44MnO2 based on hybrid electrolyte

NASA Astrophysics Data System (ADS)

Wu, Xianwen; Li, Yehua; Xiang, Yanhong; Liu, Zhixiong; He, Zeqiang; Wu, Xianming; Li, Youji; Xiong, Lizhi; Li, Chuanchang; Chen, Jian

2016-12-01

There is a broad application prospect for smart grid about aqueous rechargeable sodium-ion battery. In order to improve its electrochemical performance, a hybrid cationic aqueous-based rechargeable battery system based on the nanostructural Na0.44MnO2 and metallic zinc foil as the positive and negative electrodes respectively is built up. Nano rod-like Na0.44MnO2 is synthesized by sol-gel method followed by calcination at 850 °C for 9 h, and various characterization techniques including the X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to investigate the structure and morphology of the as-prepared material. The cyclic voltammetry, galvanostatic charge-discharge and self-discharge measurements are performed at the same time. The results show that the battery delivers a very high initial discharge capacity of 186.2 mAh g-1 at 0.2 C-rate in the range of 0.5-2.0 V, and it exhibits a discharge capacity of 113.3 mAh g-1 at high current density of 4 C-rate, indicative of excellent rate capability.

A facile hydrothermal recovery of nano sealed MnO2 particle from waste batteries: An advanced material for electrochemical and environmental applications

NASA Astrophysics Data System (ADS)

Mylarappa, M.; Venkata Lakshmi, V.; Vishnu Mahesh, K. R.; Nagaswarupa, H. P.; Raghavendra, N.

2016-09-01

This work deliberates a method for manganese (Mn) recovery as manganese oxide obtained by leaching of waste batteries with 3M sulphuric acid. The Experimental test for the recovery of Mn present within the waste dry cell batteries were carried out by a reductive leachant. Elemental composition of leached sample was confirmed by Energy Dispersive X-ray analysis (EDAX), and Surface morphology of the recovered MnO2 was examined by using Scanning Electron microscopy (SEM). Phase composition was confirmed from X-ray Diffractro meter (XRD). The obtained leached solution was treated with 4M NaOH, yielded to Manganese Dioxide with high extraction degree, while it do not touches the Zn content within the solutions. The recovered samples were characterized using XRD, EDAX, SEM and Fourier transform infrared spectrometry (FTIR). The electrochemical properties of the as-recovered sample from leached solution was examined used cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Remarkably, the 80 wt.% MnO2 displays reversibility, diffusion constant, smaller equivalent series resistance and charge transfer resistance in 0.5M NaOH showed superior results as compared to alternative electrolytes. The ideal capacitive behaviour of MnO2 electrode and nano particle was applied to photocatalytic degradation of dyes.

A new concept for high-cycle-life LEO: Rechargeable MnO2-hydrogen

NASA Technical Reports Server (NTRS)

Appleby, A. J.; Dhar, H. P.; Kim, Y. J.; Murphy, O. J.

1989-01-01

The nickel-hydrogen secondary battery system, developed in the early 1970s, has become the system of choice for geostationary earth orbit (GEO) applications. However, for low earth orbit (LEO) satellites with long expected lifetimes the nickel positive limits performance. This requires derating of the cell to achieve very long cycle life. A new system, rechargeable MnO2-Hydrogen, which does not require derating, is described here. For LEO applications, it promises to have longer cycle life, high rate capability, a higher effective energy density, and much lower self-discharge behavior than those of the nickel-hydrogen system.

Investigation on porous MnO microsphere anode for lithium ion batteries

NASA Astrophysics Data System (ADS)

Zhong, Kaifu; Zhang, Bin; Luo, Shihai; Wen, Wen; Li, Hong; Huang, Xuejie; Chen, Liquan

MnO microspheres with and without carbon coating are prepared as anode materials for lithium ion batteries. The MnO microsphere material shows a reversible capacity of 800 mAh g -1 and an initial efficiency of 71%. It can deliver 600 mAh g -1 at a rate of 400 mA g -1. Results of Mn K-edge X-ray absorption near-edge structure (XANES) spectra and extended X-ray absorption fine structure (EXAFS) confirm further the conversion reaction mechanism, indicate that pristine MnO is reduced to Mn 0 after discharging to 0 V and part of reduced Mn 0 is not oxidized to Mn 2+ after charging to 3 V. This explains the origin of the initial irreversible capacity loss partially. The quasi open circuit voltage and the relationship between the current density and the overpotential are investigated. Both indicate that there is a significant voltage difference between the charging and discharging profiles even when the current density decreases to zero.

MnO2-graphene nanosheets wrapped mesoporous carbon/sulfur composite for lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Li, Zhengzheng

2018-02-01

MnO2-graphene nanosheets wrapped mesoporous carbon/sulfur (MGN@MC/S) composite is successfully synthesized derived from metal-organic frameworks and investigated as cathode for lithium-ion batteries. Used as cathode, MGN@MC/S composite possesses electronic conductivity network for redox electron transfer and strong chemical bonding to lithium polysulfides, which enables low capacity loss to be achieved. MGN@MC/S cathodes exhibit high reversible capacity of 1475 mA h g-1 at 0.1 C and an ultra-low capacity fading of 0.042% per cycle at 1 C over 450 cycles.

(Na,□)5[MnO2]13 nanorods: a new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data

PubMed Central

Mugnaioli, Enrico; Gemmi, Mauro; Merlini, Marco; Gregorkiewitz, Michele

2016-01-01

(Nax□1 − x)5[MnO2]13 has been synthesized with x = 0.80 (4), corresponding to Na0.31[MnO2]. This well known material is usually cited as Na0.4[MnO2] and is believed to have a romanèchite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (χ2 = 0.690, R wp = 0.051, R p = 0.037, R F2 = 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) Å, β = 105.0925 (16)°, V = 918.90 (4) Å3, Z = 2. A hitherto unknown [MnO2] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by egg-shaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)5[MnO2]13. The trivalent Mn3+ ions concentrate at two of the seven Mn sites where larger Mn—O distances and Jahn–Teller distortion are observed. One of the Mn3+ sites is five-coordinated in a square pyramid which, on oxidation to Mn4+, may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures. PMID:27910840

Dissimilatory Metabolism of Nitrogen Oxides in Bacteria:Comparative Reconstruction of Transcriptional Networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodionov, Dmitry A.; Dubchak, Inna L.; Arkin, Adam P.

2005-09-01

Bacterial response to nitric oxide (NO) is of major importance since NO is an obligatory intermediate of the nitrogen cycle. Transcriptional regulation of the dissimilatory nitric oxides metabolism in bacteria is diverse and involves FNR-like transcription factors HcpR, DNR and NnrR, two-component systems NarXL and NarQP, NO-responsive activator NorR, and nitrite sensitive repressor NsrR. Using comparative genomics approaches we predict DNA-binding signals for these transcriptional factors and describe corresponding regulons in available bacterial genomes. Within the FNR family of regulators, we observed a correlation of two specificity-determining amino acids and contacting bases in corresponding DNA signal. Highly conserved regulon HcpRmore » for the hybrid cluster protein and some other redox enzymes is present in diverse anaerobic bacteria including Clostridia, Thermotogales and delta-proteobacteria. NnrR and DNR control denitrification in alpha- and beta-proteobacteria, respectively. Sigma-54-dependent NorR regulon found in some gamma- and beta-proteobacteria contains various enzymes involved in the NO detoxification. Repressor NsrR, which was previously known to control only nitrite reductase operon in Nitrosomonas spp., appears to be the master regulator of the nitric oxides metabolism not only in most gamma- and beta-proteobacteria (including well-studied species like Escherichia coli), but also in Gram-positive Bacillus and Streptomyces species. Positional analysis and comparison of regulatory regions of NO detoxification genes allows us to propose the candidate NsrR-binding signal. The most conserved member of the predicted NsrR regulon is the NO-detoxifying flavohemoglobin Hmp. In enterobacteria, the regulon includes also two nitrite-responsive loci, nipAB (hcp-hcr) and nipC(dnrN), thus confirming the identity of the effector, i.e., nitrite. The proposed NsrR regulons in Neisseria and some other species are extended to include denitrification genes. As

Facile fabrication of MnO x and N co-doped hierarchically porous carbon microspheres for high-performance supercapacitors

DOE PAGES

Yang, Ying; Yang, Feng; Lee, Sungsik; ...

2016-01-16

Facile fabrication of manganese oxide (MnO x, 0 < x < 2) and nitrogen (N) co-doped carbon microspheres (MnO x-N-CS) has been firstly developed by one-pot construction of Mn-functionalized melamine-formaldehyde (Mn-MF) resin spheres before pyrolysis. The resulting hybrids bear evenly dispersed MnO x and N moieties in situ anchored on hierarchically porous carbon microspheres formed simultaneously. The capacitive performance is greatly tailored by varying the Mn/melamine molar ratio in the synthetic mixture and pyrolysis temperature. It is found that the MnO x-N-CS hybrid (0.008 wt% Mn, pyrolyzed at 800 °C) exhibits the highest specific capacitance up to 258 F gmore » –1 at a scan rate of 1 mV s –1 (in 6 M KOH), and keeps a high capacitance retention ratio of 98% after 5000 cycles. The synergism between MnO x, N moieties and carbon spheres proves to be responsible for the remarkably improved performance, as compared to the pure carbon sphere and MnO x (N)-doped carbon sphere. Lastly, the well-developed MnO x-N-CS hybrids highlight the great potentials for widespread supercapacitor applications.« less

Detailed study of the magnetic behaviour at low scale in La2/3Sr1/3MnO3

NASA Astrophysics Data System (ADS)

Arango, I. C.; E Ordoñez, J.; Dominguez, C.; Arango, C.; E Gomez, M.

2017-12-01

The La2/3Sr1/3MnO3 (LSMO) with Curie temperature above room temperature is the leading compound of the manganite perovskite family. Therefore, the physical properties are desirable for practical applications as magnetic sensors. However, when the dimensions are reduced the ferromagnetic properties of material are weakened. In this research, we have grown La2/3Sr1/3MnO3/SrTiO3 thin films by sputtering DC at high oxygen pressure at 830°C. X-Ray Diffraction (XRD) analysis reveals that only (0 0 2) LSMO peak are present, indicating a textured growth. The samples morphology was characterized by Atomic Force Microscopy (AFM). Additionally, LSMO microwires were patterned by UV lithography; the devices are a well-defined channel with current and voltage leads enabling four points resistance measurements. Resistivity versus temperature curves displays typical manganite behaviour with metal-insulator transition ∼350K. We study the electric and magnetotransport properties in LSMO film and in wire channel and their dependence with size (width and length) for potential applications like magnetic sensors.

Structural and thermoelectric properties of n-type Sr1- x Ti x MnO3- δ perovskite system

NASA Astrophysics Data System (ADS)

Kim, C. M.; Seo, J. W.; Choi, S.-M.; Seo, W.-S.; Lee, S.; Lim, Y. S.; Park, K.

2015-03-01

A series of Sr1- x Ti x MnO3- δ (0.05 ≤ x ≤ 0.3) was fabricated by the solid-state reaction method. We studied the structural and thermoelectric properties of Sr1- x Ti x MnO3- δ , with respect to the partial substitution of Ti4+ for Sr2+. The sintered Sr1- x Ti x MnO3- δ crystallized in the hexagonal perovskite-type structure with a space group of P6 3 / mmc. For x ≤ 0.1, the partial substitution of Ti4+ for Sr2+ led to increases in the electrical conductivity and the absolute value of the Seebeck coefficient, thus enhancing the power factor. The highest power factor (2.5 × 10-5 Wm-1K-2) was obtained for Sr0.9Ti0.1MnO3- δ at 800°C. The partial substitution of Ti4+ for Sr2+ in SrMnO3- δ led to a significant improvement in the thermoelectric properties. [Figure not available: see fulltext.

Aluminum and sulphate removal by a highly Al-resistant dissimilatory sulphate-reducing bacteria community.

PubMed

Martins, Mónica; Taborda, Rita; Silva, Gonçalo; Assunção, Ana; Matos, António Pedro; Costa, Maria Clara

2012-09-01

A highly Al-resistant dissimilatory sulphate-reducing bacteria community was isolated from sludge of the wetland of Urgeiriça mine (community W). This community showed excellent sulphate removal at the presence of Al³⁺. After 27 days of incubation, 73, 86 and 81% of sulphate was removed in the presence of 0.48, 0.90 and 1.30 mM of Al³⁺, respectively. Moreover, Al³⁺ was simultaneously removed: 55, 85 and 78% of metal was removed in the presence of 0.48, 0.90 and 1.30 mM of Al³⁺, respectively. The dissociation of aluminium-lactate soluble complexes due to lactate consumption by dissimilatory sulphate-reducing bacteria can be responsible for aluminum removal, which probably precipitates as insoluble aluminium hydroxide. Phylogenetic analysis of 16S rRNA gene showed that this community was mainly composed by bacteria closely related to Desulfovibrio desulfuricans. However, bacteria affiliated to Proteus and Ralstonia were also present in the community.

Mechanism of H2S Oxidation by the Dissimilatory Perchlorate-Reducing Microorganism Azospira suillum PS

PubMed Central

Mehta-Kolte, Misha G.; Loutey, Dana; Wang, Ouwei; Youngblut, Matthew D.; Hubbard, Christopher G.; Wetmore, Kelly M.; Conrad, Mark E.

2017-01-01

ABSTRACT The genetic and biochemical basis of perchlorate-dependent H2S oxidation (PSOX) was investigated in the dissimilatory perchlorate-reducing microorganism (DPRM) Azospira suillum PS (PS). Previously, it was shown that all known DPRMs innately oxidize H2S, producing elemental sulfur (So). Although the process involving PSOX is thermodynamically favorable (ΔG°′ = −206 kJ ⋅ mol−1 H2S), the underlying biochemical and genetic mechanisms are currently unknown. Interestingly, H2S is preferentially utilized over physiological electron donors such as lactate or acetate although no growth benefit is obtained from the metabolism. Here, we determined that PSOX is due to a combination of enzymatic and abiotic interactions involving reactive intermediates of perchlorate respiration. Using various approaches, including barcode analysis by sequencing (Bar-seq), transcriptome sequencing (RNA-seq), and proteomics, along with targeted mutagenesis and biochemical characterization, we identified all facets of PSOX in PS. In support of our proposed model, deletion of identified upregulated PS genes traditionally known to be involved in sulfur redox cycling (e.g., Sox, sulfide:quinone reductase [SQR]) showed no defect in PSOX activity. Proteomic analysis revealed differential abundances of a variety of stress response metal efflux pumps and divalent heavy-metal transporter proteins, suggesting a general toxicity response. Furthermore, in vitro biochemical studies demonstrated direct PSOX mediated by purified perchlorate reductase (PcrAB) in the absence of other electron transfer proteins. The results of these studies support a model in which H2S oxidation is mediated by electron transport chain short-circuiting in the periplasmic space where the PcrAB directly oxidizes H2S to So. The biogenically formed reactive intermediates (ClO2− and O2) subsequently react with additional H2S, producing polysulfide and So as end products. PMID:28223460

Voltage controlled Bi-mode resistive switching effects in MnO2 based devices

NASA Astrophysics Data System (ADS)

Hu, P.; Wu, S. X.; Wang, G. L.; Li, H. W.; Li, D.; Li, S. W.

2018-01-01

In this paper, the voltage induced bi-mode resistive switching behavior of an MnO2 thin film based device was studied. The device showed prominent bipolar resistive switching behavior with good reproducibility and high endurance. In addition, complementary resistive switching characteristics can be observed by extending the voltage bias during voltage sweep operations. The electrical measurement data and fitting results indicate that the oxygen vacancies act as defects to form a conductive path, which is connective or disrupted to realize a low resistive state or a high resistive state. Changing the sweep voltage can tune the oxygen vacancies distribution, which will achieve complementary resistive switching.

An Asymmetric Supercapacitor with Both Ultra-High Gravimetric and Volumetric Energy Density Based on 3D Ni(OH)2/MnO2@Carbon Nanotube and Activated Polyaniline-Derived Carbon.

PubMed

Shen, Juanjuan; Li, Xiaocheng; Wan, Liu; Liang, Kun; Tay, Beng Kang; Kong, Lingbin; Yan, Xingbin

2017-01-11

Development of a supercapacitor device with both high gravimetric and volumetric energy density is one of the most important requirements for their practical application in energy storage/conversion systems. Currently, improvement of the gravimetric/volumetric energy density of a supercapacitor is restricted by the insufficient utilization of positive materials at high loading density and the inferior capacitive behavior of negative electrodes. To solve these problems, we elaborately designed and prepared a 3D core-shell structured Ni(OH) 2 /MnO 2 @carbon nanotube (CNT) composite via a facile solvothermal process by using the thermal chemical vapor deposition grown-CNTs as support. Owing to the superiorities of core-shell architecture in improving the service efficiency of pseudocapacitive materials at high loading density, the prepared Ni(OH) 2 /MnO 2 @CNT electrode demonstrated a high capacitance value of 2648 F g -1 (1 A g -1 ) at a high loading density of 6.52 mg cm -2 . Coupled with high-performance activated polyaniline-derived carbon (APDC, 400 F g -1 at 1 A g -1 ), the assembled Ni(OH) 2 /MnO 2 @CNT//APDC asymmetric device delivered both high gravimetric and volumetric energy density (126.4 Wh kg -1 and 10.9 mWh cm -3 , respectively), together with superb rate performance and cycling lifetime. Moreover, we demonstrate an effective approach for building a high-performance supercapacitor with high gravimetric/volumetric energy density.

Anaerobes into heavy metal: Dissimilatory metal reduction in anoxic environments

USGS Publications Warehouse

Lovley, D.R.

1993-01-01

Within the last decade, a novel form of microbial metabolism of major environmental significance has been elucidated. In this process, known as dissimilatory metal reduction, specialized microorganisms, living in anoxic aquatic sediments and ground water, oxidize organic compounds to carbon dioxide with metals serving as the oxidant. Recent studies have demonstrated that this metabolism explains a number of important geochemical phenomena in ancient and modern sedimentary environments, affecting not only the cycling of metals but also the fate of organic matter. Furthermore, this metabolism may have practical application in remediation of environments contaminated with toxic metals and/or organics.

Bacterial respiration of arsenic and selenium

USGS Publications Warehouse

Stolz, J.F.; Oremland, R.S.

1999-01-01

Oxyanions of arsenic and selenium can be used in microbial anaerobic respiration as terminal electron acceptors. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram- positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated.

Hybrid MnO2/carbon nanotube-VN/carbon nanotube supercapacitors

NASA Astrophysics Data System (ADS)

Su, Y.; Zhitomirsky, I.

2014-12-01

Composite materials, containing fibrous VN nanoparticles and multiwalled carbon nanotubes (MWCNT) are prepared by a chemical method for application in electrochemical supercapacitors. We demonstrate for the first time that VN-MWCNT electrodes exhibit good capacitive behavior in 0.5 M Na2SO4 electrolyte in a negative voltage window of 0.9 V. Quartz crystal microbalance studies provide an insight into the mechanism of charge storage. Composite VN-MWCNT materials show significant improvement in capacitance, compared to individual VN and MWCNT materials. Testing results indicate that VN-MWCNT electrodes exhibit high specific capacitance at high mass loadings in the range of 10-30 mg cm-2, good capacitance retention at scan rates in the range of 2-200 mV s-1 and good cycling stability. The highest specific capacitance of 160 F g-1 is achieved at a scan rate of 2 mV s-1. The new findings open a new and promising strategy in the fabrication of hybrid devices based on VN. The proof-of-principle is demonstrated by the fabrication of hybrid supercapacitor devices based on VN-MWCNT negative electrodes and MnO2 -MWCNT positive electrodes with voltage window of 1.8 V in aqueous 0.5 M Na2SO4 electrolyte. The hybrid VN-MWCNT/MnO2-MWCNT supercapacitor cells show promising capacitive and power-energy characteristics.

High-energy MnO2 nanowire/graphene and graphene asymmetric electrochemical capacitors.

PubMed

Wu, Zhong-Shuai; Ren, Wencai; Wang, Da-Wei; Li, Feng; Liu, Bilu; Cheng, Hui-Ming

2010-10-26

In order to achieve high energy and power densities, we developed a high-voltage asymmetric electrochemical capacitor (EC) based on graphene as negative electrode and a MnO(2) nanowire/graphene composite (MGC) as positive electrode in a neutral aqueous Na(2)SO(4) solution as electrolyte. MGC was prepared by solution-phase assembly of graphene sheets and α-MnO(2) nanowires. Such aqueous electrolyte-based asymmetric ECs can be cycled reversibly in the high-voltage region of 0-2.0 V and exhibit a superior energy density of 30.4 Wh kg(-1), which is much higher than those of symmetric ECs based on graphene//graphene (2.8 Wh kg(-1)) and MGC//MGC (5.2 Wh kg(-1)). Moreover, they present a high power density (5000 W kg(-1) at 7.0 Wh kg(-1)) and acceptable cycling performance of ∼79% retention after 1000 cycles. These findings open up the possibility of graphene-based composites for applications in safe aqueous electrolyte-based high-voltage asymmetric ECs with high energy and power densities.

Ultrafine MnO2 Nanowire Arrays Grown on Carbon Fibers for High-Performance Supercapacitors

NASA Astrophysics Data System (ADS)

Hu, Jiyu; Qian, Feng; Song, Guosheng; Li, Wenyao; Wang, Linlin

2016-10-01

Large-area ultrafine MnO2 nanowire arrays (NWA) directly grew on a carbon fiber (CF, used as a substrate) by a simple electrochemical method, forming three-dimensional (3D) hierarchical heterostructures of a CF@MnO2 NWA composite. As an electrode for supercapacitors, the CF@MnO2 NWA composite exhibits excellent electrochemical performances including high specific capacitance (321.3 F g-1 at 1000 mA g-1) and good rate capability. Further, the overall capacitance retention is 99.7 % capacitance after 3000 cycles. These outstanding electrochemical performances attribute to a large number of transport channels for the penetration of electrolyte and the transportation of ions and electrons of electrodes. The as-prepared CF@MnO2 NWA composite may be a promising electrode material for high-performance supercapacitors.

MnO2 nanotubes assembled on conductive graphene/polyester composite fabric as a three-dimensional porous textile electrode for flexible electrochemical capacitors.

PubMed

Jin, Chun; Jin, Li-Na; Guo, Mei-Xia; Liu, Ping; Zhang, Jia-Nan; Bian, Shao-Wei

2017-12-15

A three-dimensional (3D) electrode material was successfully synthesized through a facile ZnO-assisted hydrothermal process in which vertical MnO 2 nanotube arrays were in situ grown on the conductive graphene/polyester composite fabric. The morphology and structure of MnO 2 nanotubes/graphene/polyester textile electrode were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The 3D electrode structure facilitates to achieve the maximum number of active sites for the pesudocapacitance redox reaction, fast electrolyte ion transportation and short ion diffusion path. The electrochemical measurements showed that the electrode possesses good capacitance capacity which reached 498F/g at a scan rate of 2mV/s in Na 2 SO 4 electrolyte solution. The electrode also showed stable electrochemical performances under the conditions of long-term cycling, and mechanical bending and twisting. Copyright © 2017 Elsevier Inc. All rights reserved.

Size effect on the magnetic properties of antiferromagnetic La0.2Ca0.8MnO3 nanoparticles

NASA Astrophysics Data System (ADS)

Markovich, V.; Fita, I.; Wisniewski, A.; Mogilyansky, D.; Puzniak, R.; Titelman, L.; Martin, C.; Gorodetsky, G.

2010-03-01

Magnetic properties of electron-doped La0.2Ca0.8MnO3 manganite nanoparticles with average particle size ranging from 15 to 37 nm, prepared by the glycine-nitrate method, have been investigated in temperature range 5-300 K and in magnetic fields up to 90 kOe. A monotonous enhancement of weak ferromagnetism linked to the reduction in the particle size was observed for all nanoparticles. Magnetic hysteresis loops also indicate size-dependent exchange bias effect displayed by horizontal and vertical shifts in field-cooled processes. The magnetization data reveal two ferromagnetic components: first one appears at T˜200K and may be attributed to surface magnetization and second one appears as a result of spin canting of antiferromagnetic core or is developed at some interfaces inside nanoparticles. Time evolution of magnetization recorded in magnetic fields after the field cooling to low temperatures exhibits a very noisy behavior that may be caused by formation of collective state of nanoparticles with no clear tendency to reach equilibrium state. Magnetic properties of the nanoparticle samples are compared with those of the bulk La0.2Ca0.8MnO3 .

Ti-substituted tunnel-type Na 0.44MnO 2 oxide as a negative electrode for aqueous sodium-ion batteries

DOE PAGES

Wang, Yuesheng; Liu, Jue; Lee, Byungju; ...

2015-03-25

The aqueous sodium-ion battery system is a safe and low-cost solution for large-scale energy storage, due to the abundance of sodium and inexpensive aqueous electrolytes. Although several positive electrode materials, e.g., Na 0.44MnO 2, were proposed, few negative electrode materials, e.g., activated carbon and NaTi 2(PO 4) 3, are available. Here we show that Ti-substituted Na 0.44MnO 2 (Na 0.44[Mn 1-xTi x]O 2) with tunnel structure can be used as a negative electrode material for aqueous sodium-ion batteries. This material exhibits superior cyclability even without the special treatment of oxygen removal from the aqueous solution. Atomic-scale characterizations based on sphericalmore » aberration-corrected electron microscopy and ab initio calculations are utilized to accurately identify the Ti substitution sites and sodium storage mechanism. Ti substitution tunes the charge ordering property and reaction pathway, significantly smoothing the discharge/charge profiles and lowering the storage voltage. Both the fundamental understanding and practical demonstrations suggest that Na 0.44[Mn 1-xTi x]O 2 is a promising negative electrode material for aqueous sodium-ion batteries.« less

Identification and characterization of a bacterial hydrosulphide ion channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Czyzewski, Bryan K.; Wang, Da-Neng

2012-10-26

The hydrosulphide ion (HS{sup -}) and its undissociated form, hydrogen sulphide (H{sub 2}S), which are believed to have been critical to the origin of life on Earth, remain important in physiology and cellular signalling. As a major metabolite in anaerobic bacterial growth, hydrogen sulphide is a product of both assimilatory and dissimilatory sulphate reduction. These pathways can reduce various oxidized sulphur compounds including sulphate, sulphite and thiosulphate. The dissimilatory sulphate reduction pathway uses this molecule as the terminal electron acceptor for anaerobic respiration, in which process it produces excess amounts of H{sub 2}S. The reduction of sulphite is a keymore » intermediate step in all sulphate reduction pathways. In Clostridium and Salmonella, an inducible sulphite reductase is directly linked to the regeneration of NAD{sup +}, which has been suggested to have a role in energy production and growth, as well as in the detoxification of sulphite. Above a certain concentration threshold, both H{sub 2}S and HS{sup -} inhibit cell growth by binding the metal centres of enzymes and cytochrome oxidase, necessitating a release mechanism for the export of this toxic metabolite from the cell. Here we report the identification of a hydrosulphide ion channel in the pathogen Clostridium difficile through a combination of genetic, biochemical and functional approaches. The HS{sup -} channel is a member of the formate/nitrite transport family, in which about 50 hydrosulphide ion channels form a third subfamily alongside those for formate (FocA) and for nitrite (NirC). The hydrosulphide ion channel is permeable to formate and nitrite as well as to HS{sup -} ions. Such polyspecificity can be explained by the conserved ion selectivity filter observed in the channel's crystal structure. The channel has a low open probability and is tightly regulated, to avoid decoupling of the membrane proton gradient.« less

The location of dissimilatory nitrite reductase and the control of dissimilatory nitrate reductase by oxygen in Paracoccus denitrificans.

PubMed Central

Alefounder, P R; Ferguson, S J

1980-01-01

1. A method is described for preparing spheroplasts from Paracoccus denitrificans that are substantially depleted of dissimilatory nitrate reductase (cytochrome cd) activity. Treatment of cells with lysozyme + EDTA together with a mild osmotic shock, followed by centrifugation, yielded a pellet of spheroplasts and a supernatant that contained d-type cytochrome. The spheroplasts were judged to have retained an intact plasma membrane on the basis that less than 1% of the activity of a cytoplasmic marker protein, malate dehydrogenase, was released from the spheroplasts. In addition to a low activity towards added nitrite, the suspension of spheroplasts accumulated the nitrite that was produced by respiratory chain-linked reduction of nitrate. It is concluded that nitrate reduction occurs at the periplasmic side of the plasma membrane irrespective of whether nitrite is generated by nitrate reduction or is added exogenously. 2. Further evidence for the integrity of the spheroplasts was that nitrate reduction was inhibited by O2, and that chlorate was reduced at a markedly lower rate than nitrate. These data are taken as evidence for an intact plasma membrane because it was shown that cells acquire the capability to reduce nitrate under aerobic conditions after addition of low amounts of Triton X-100 which, with the same titre, also overcame the permeability barrier to chlorate reduction by intact cells. The close relationship between the appearance of chlorate reduction and the loss of the inhibitory effect of O2 on nitrate reduction also suggests that the later feature of nitrate respiration is due to a control on the accessibility of nitrate to its reductase rather than on the flow of electrons to nitrate reductase. PMID:7197918

Ultrafine MnO2 Nanowire Arrays Grown on Carbon Fibers for High-Performance Supercapacitors.

PubMed

Hu, Jiyu; Qian, Feng; Song, Guosheng; Li, Wenyao; Wang, Linlin

2016-12-01

Large-area ultrafine MnO 2 nanowire arrays (NWA) directly grew on a carbon fiber (CF, used as a substrate) by a simple electrochemical method, forming three-dimensional (3D) hierarchical heterostructures of a CF@MnO 2 NWA composite. As an electrode for supercapacitors, the CF@MnO 2 NWA composite exhibits excellent electrochemical performances including high specific capacitance (321.3 F g -1 at 1000 mA g -1 ) and good rate capability. Further, the overall capacitance retention is ~99.7 % capacitance after 3000 cycles. These outstanding electrochemical performances attribute to a large number of transport channels for the penetration of electrolyte and the transportation of ions and electrons of electrodes. The as-prepared CF@MnO 2 NWA composite may be a promising electrode material for high-performance supercapacitors.

Enhanced microwave absorption properties of epoxy composites containing graphite nanosheets@Fe3O4 decorated comb-like MnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Su, Xiaogang; Wang, Jun; Zhang, Bin; Chen, Wei; Wu, Qilei; Dai, Wei; Zou, Yi

2018-05-01

Recently, owing to the radiation and interference from electromagnetic wave (EMW), the requirements of EMW absorbing materials have been increasing. Herein, a novel absorber composed of graphite nanosheets@Fe3O4 composites decorated comb-like MnO2 (GNFM) has been successfully synthesized via a facile two steps, characterized using x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, vibrating sample magnetometry (VSM) and vector network analyzer (VNA). The ternary composites with enhanced microwave absorption performance are due to the complementary effects of electroconductive material (graphite nanosheets), dielectric materials (MnO2) and magnetic material (Fe3O4 nanospheres). Hence, the maximum reflection loss of GNFM/epoxy composites is up to ‑31.7 dB at 5.85 GHz with absorbing thickness of 4.5 mm, and the efficient frequency bandwidth below ‑10 dB can reach up to 4.47 GHz (11.87–16.34 GHz) at matching thickness of 2 mm. The results demonstrate that GNFM could be regarded as a novel type of microwave absorbing material.

Interfacial coupling in multiferroic BiFeO3 and ferromagnetic La2/3Sr1/3MnO3 thin films

NASA Astrophysics Data System (ADS)

Dominguez, C.; E Ordoñez, J.; E Gomez, M.

2017-12-01

Antiferromagnetic/Ferromagnetic coupling mechanics have been studying by growing successfully BiFeO3/La2/3Sr1/3MnO3 bilayers on SrTiO3 single crystals by using rf and dc sputtering technique at pure oxygen pressures. We have investigated the magnetic behaviour of this samples, field cooling loops evidence interfacial coupling effect when antiferromagnetic ferroelectric BiFeO3 is placed in contact with ferromagnetic La2/3Sr1/3MnO3 indicate by the shift of the magnetization loop to negative values of the applied magnetic field. Our samples exhibited an exchange bias of 76Oe at 5K after field cooling the sample under 5000Oe. Temperature dependence of the exchange bias field showed exponential decay. The BFO/LSMO bilayer exhibits excellent ferroelectric behaviour (Ps=65μC/cm2 at 4V and 100Hz). Coexistence of ferroelectric and ferromagnetic properties in the BFO/LSMO bilayer make it a promising candidate system for applications where the magnetoelectric behaviour is required.

Effects of lattice deformation on magnetic properties of electron-doped La0.8Hf0.2MnO3 thin films

NASA Astrophysics Data System (ADS)

Wu, Z. P.; Jiang, Y. C.; Gao, J.

2013-05-01

The lattice deformation effects on electric and magnetic properties of electron-doped La0.8Hf0.2MnO3 (LHMO) thin films have been systematically investigated. LHMO films with various thicknesses (15 nm, 40 nm, and 80 nm) were grown on (001) SrTiO3 and (001) LaAlO3 substrates, which induces in-plane tensile and compressive biaxial stress, respectively. The metal-insulator phase transition temperature (TP) and magnetoresistance (MR) effect show a strong dependence on film thickness. TP increases with a decrease in thickness and is enhanced as the lattice strain rises, regardless of whether it is tensile or compressive. The maximum MR ratio is suppressed by reduction of the film thickness. These anomalous phenomena may be attributed to the competition between the strain induced modification of the Mn-O bond length and the eg orbital stability.

Redox states of Desulfovibrio vulgaris DsrC, a key protein in dissimilatory sulfite reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venceslau, Sofia S.; Cort, John R.; Baker, Erin S.

2013-11-29

Highlights: •DsrC is known to interact with the dissimilatory sulfite reductase enzyme (DsrAB). •We show that, however, most cellular DsrC is not associated with DsrAB. •A gel-shift assay was developed that allows monitoring of the DsrC redox state. •The DsrC intramolecularly oxidized state could only be produced by arginine treatment. -- Abstract: Dissimilatory reduction of sulfite is carried out by the siroheme enzyme DsrAB, with the involvement of the protein DsrC, which has two conserved redox-active cysteines. DsrC was initially believed to be a third subunit of DsrAB. Here, we report a study of the distribution of DsrC in cellmore » extracts to show that, in the model sulfate reducer Desulfovibrio vulgaris, the majority of DsrC is not associated with DsrAB and is thus free to interact with other proteins. In addition, we developed a cysteine-labelling gel-shift assay to monitor the DsrC redox state and behaviour, and procedures to produce the different redox forms. The oxidized state of DsrC with an intramolecular disulfide bond, which is proposed to be a key metabolic intermediate, could be successfully produced for the first time by treatment with arginine.« less

Phylogenetic and environmental diversity of DsrAB-type dissimilatory (bi)sulfite reductases

PubMed Central

Müller, Albert Leopold; Kjeldsen, Kasper Urup; Rattei, Thomas; Pester, Michael; Loy, Alexander

2015-01-01

The energy metabolism of essential microbial guilds in the biogeochemical sulfur cycle is based on a DsrAB-type dissimilatory (bi)sulfite reductase that either catalyzes the reduction of sulfite to sulfide during anaerobic respiration of sulfate, sulfite and organosulfonates, or acts in reverse during sulfur oxidation. Common use of dsrAB as a functional marker showed that dsrAB richness in many environments is dominated by novel sequence variants and collectively represents an extensive, largely uncharted sequence assemblage. Here, we established a comprehensive, manually curated dsrAB/DsrAB database and used it to categorize the known dsrAB diversity, reanalyze the evolutionary history of dsrAB and evaluate the coverage of published dsrAB-targeted primers. Based on a DsrAB consensus phylogeny, we introduce an operational classification system for environmental dsrAB sequences that integrates established taxonomic groups with operational taxonomic units (OTUs) at multiple phylogenetic levels, ranging from DsrAB enzyme families that reflect reductive or oxidative DsrAB types of bacterial or archaeal origin, superclusters, uncultured family-level lineages to species-level OTUs. Environmental dsrAB sequences constituted at least 13 stable family-level lineages without any cultivated representatives, suggesting that major taxa of sulfite/sulfate-reducing microorganisms have not yet been identified. Three of these uncultured lineages occur mainly in marine environments, while specific habitat preferences are not evident for members of the other 10 uncultured lineages. In summary, our publically available dsrAB/DsrAB database, the phylogenetic framework, the multilevel classification system and a set of recommended primers provide a necessary foundation for large-scale dsrAB ecology studies with next-generation sequencing methods. PMID:25343514

Hierarchically MnO2-Nanosheet Covered Submicrometer-FeCo2O4-Tube Forest as Binder-Free Electrodes for High Energy Density All-Solid-State Supercapacitors.

PubMed

Zhu, Baogang; Tang, Shaochun; Vongehr, Sascha; Xie, Hao; Meng, Xiangkang

2016-02-01

The current problem of the still relatively low energy densities of supercapacitors can be effectively addressed by designing electrodes hierarchically on micro- and nanoscale. Herein, we report the synthesis of hierarchically porous, nanosheet covered submicrometer tube forests on Ni foam. Chemical deposition and thermal treatment result in homogeneous forests of 750 nm diameter FeCo2O4 tubes, which after hydrothermal reaction in KMnO4 are wrapped in MnO2-nanosheet-built porous covers. The covers' thickness can be adjusted from 200 to 800 nm by KMnO4 concentration. An optimal thickness (380 nm) with a MnO2 content of 42 wt % doubles the specific capacitance (3.30 F cm(-2) at 1.0 mA cm(-2)) of the bare FeCo2O4-tube forests. A symmetric solid-state supercapacitor made from these binder-free electrodes achieves 2.52 F cm(-2) at 2 mA cm(-2), much higher than reported for capacitors based on similar core-shell nanowire arrays. The large capacitance and high cell voltage of 1.7 V allow high energy and power densities (93.6 Wh kg(-1), 10.1 kW kg(-1)). The device also exhibits superior rate capability (71% capacitance at 20 mA cm(-2)) and remarkable cycling stability with 94% capacitance retention being stable after 1500 cycles.

Magneto-reactance based detection of MnO nanoparticle-embedded Lewis lung carcinoma cells

NASA Astrophysics Data System (ADS)

Devkota, J.; Howell, M.; Mukherjee, P.; Srikanth, H.; Mohapatra, S.; Phan, M. H.

2015-05-01

We demonstrate the capacity of detecting magnetically weak manganese oxide (MnO) nanoparticles and the Lewis lung carcinoma (LLC) cancer cells that have taken up these nanoparticles using a novel biosensor based on the magneto-reactance (MX) effect of a soft ferromagnetic amorphous ribbon with a microhole-patterned surface. While the magnetic moment of the MnO nanoparticles is relatively small, and a magneto-impedance based sensor fails to detect them in solution (0.05 mg/ml manganese oxide lipid micellar nanoparticles) and inside cells at low concentrations (8.25 × 104 cells/ml), the detection of these nanoparticles and the LLC cells containing them is achieved with the MX-based sensor, which, respectively, reaches the detection sensitivity of ˜3.6% and 2.8% as compared to the blank cells. Since the MnO nanoparticles are a promising contrast agent for magnetic resonance imaging (MRI) of lung cells, the MX-based biosensing technique can be developed as a pre-detection method for MRI of lung cancer cells.

Positive magnetoresistance of La0.7Sr0.3MnO3/C composites

NASA Astrophysics Data System (ADS)

Kabirov, Yu. V.; Gavrilyachenko, V. G.; Bogatin, A. S.

2016-07-01

The perovskite manganite La0.7Sr0.3MnO3 compound is used as a component in ceramic (1-x)(La0.7Sr0.3MnO3)-xC composites at x = 0.15-0.85. It is found that every studied specimen is characterized by the linear dependence of the positive magnetoresistance (PMR) on the magnetic field strength at room temperature. The 0.6(La0.7Sr0.3MnO3)-0.4C composite has the largest magnetoresistance value (15%) at room temperature and intensity of magnetic field H=15kOe. A possible mechanism for the PMR of (1-x)(La0.7Sr0.3MnO3)-xC composites is discussed.

Fabrication and Properties of Cr2O3 and La0.7Sr0.3MnO3 Thin Film Heterostructures Integrated on Si(001)

NASA Astrophysics Data System (ADS)

Punugupati, Sandhyarani

Spintronics that utilizes both the spin and charge degrees of freedom of an electron is emerged as an alternate memory technology to conventional CMOS electronics. Many proposed spintronic devices require multifunctional properties in a single material. The oxides Cr2O3 and La0.7Sr0.3MnO3 are such materials which exhibit unique physical properties at room temperature. The Cr2O3 is an antiferromagnetic and magnetoelectric material below its Neel temperature 307K. The La0.7Sr0.3MnO3 is a ferromagnetic half metal with a Curie temperature of 360K and exhibits colossal magnetoresistance. However, the reach of this spintronic technology into more device applications is possible only when these materials in epitaxial thin film form are integrated with Si(001) which is the mainstay substrate in semiconductor industry. The primary objective of this dissertation was to integrate epitaxial Cr2O3, La0.7Sr0.3MnO3 and Cr2O3/La0.7Sr0.3MnO3 thin film heterostructure on Si(001) and, study their physical properties to investigate structure-processing-property relationship in these heterostructures. The epitaxial integration of Cr2O3 thin films on Si(001) was done using epitaxial cubic yttria stabilized zirconia (c-YSZ) buffer layer by pulsed laser deposition. Detailed structural characterizations XRD (2theta and phi) and TEM confirm the epitaxial nature of the films. Though bulk Cr2O3 is antiferromagnetic along the c-axis, the in-plane magnetization measurements on Cr2O3(0001) thin films showed ferromagnetic behavior up to 400K. The thickness dependent magnetization together with oxygen annealing results suggested that the in-plane ferromagnetism in Cr2O3 was due to the oxygen related defects whose concentration is controlled by strain in the films. The out-of-plane magnetic measurements on Cr2O3(0001) films showed magnetic behavior indicative of antiferromagnetic nature. To verify whether ferromagnetism can be induced by strain in Cr 2O3 thin films with orientation other than (0001

Manganese Recovery by Silicothermic Reduction of MnO in BaO-MnO-MgO-CaF2 (-SiO2) Slags

NASA Astrophysics Data System (ADS)

Heo, Jung Ho; Park, Joo Hyun

2018-04-01

The effects of reducing agent, CaF2 content, and reaction temperature upon the silicothermic reduction of MnO in the BaO-MnO-MgO-CaF2 (-SiO2) slags were investigated. Mn recovery was proportional to Si activity in the molten alloy. Moreover, 90 pct yield of Mn recovery was obtained under 5 mass pct CaF2 content and 1873 K (1600 °C) reaction temperature. Increasing CaF2 content above 5 pct yielded little or no further increase in Mn recovery, because it was accompanied by increased slag viscosity owing to the precipitation of high melting point compounds such as Ba2SiO4.

Stretchable Fiber Supercapacitors with High Volumetric Performance Based on Buckled MnO2 /Oxidized Carbon Nanotube Fiber Electrodes.

PubMed

Li, Mingyang; Zu, Mei; Yu, Jinshan; Cheng, Haifeng; Li, Qingwen

2017-03-01

A stretchable fiber supercapacitor (SC) based on buckled MnO 2 /oxidized carbon nanotube (CNT) fiber electrode is fabricated by a simple prestraining-then-buckling method. The prepared stretchable fiber SC has a specific volumetric capacitance up to 409.4 F cm -3 , which is 33 times that of the pristine CNT fiber based SC, and shows the outstanding stability and repeatability in performance as a stretchable SC. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Estimation of the magnetic entropy change by means of Landau theory and phenomenological model in La0.6Ca0.2 Sr0.2MnO3/Sb2O3 ceramic composites

NASA Astrophysics Data System (ADS)

Nasri, M.; Dhahri, E.; Hlil, E. K.

2018-06-01

In this paper, magnetocaloric properties of La0.6Ca0.2Sr0.2MnO3/Sb2O3 oxides have been investigated. The composite samples were prepared using the conventional solid-state reaction method. The second-order phase transition can be testified with the positive slope in Arrott plots. An excellent agreement has been found between the -ΔSM values estimated by Landau theory and those obtained using the classical Maxwell relation. The field dependence of the magnetic entropy change analysis shows a power law dependence,|ΔSM|≈Hn , with n(TC) = 0.65. Moreover, the scaling analysis of magnetic entropy change exhibits that ΔSM(T) curves collapse into a single universal curve, indicating that the observed paramagnetic to ferromagnetic phase transition is an authentic second-order phase transition. The maximum value of magnetic entropy change of composites is found to decrease slightly with the further increasing of Sb2O3 concentration. A phenomenological model was used to predict magnetocaloric properties of La0.6Ca0.2Sr0.2MnO3/Sb2O3 composites. The theoretical calculations are compared with the available experimental data.

Surface multiheme c-type cytochromes from Thermincola potens: Implications for dissimilatory metal reduction by Gram-positive bacteria

NASA Astrophysics Data System (ADS)

Carlson, H. K.; Iavarone, A. T.; Gorur, A.; Yeo, B. S.; Tran, R.; Melnyk, R. A.; Mathies, R. A.; Auer, M.; Coates, J. D.

2011-12-01

Almost nothing is known about the mechanisms of dissimilatory metal reduction by Gram-positive bacteria, although they have been shown to be the dominant species in some environments. Thermincola potens strain JR was isolated from the anode of a microbial fuel cell inoculated with anaerobic digester sludge and operated at 55 °C. Preliminary characterization revealed that T. potens coupled acetate oxidation to the reduction of hydrous ferric oxides (HFO) or the humic substances analog, anthraquinone-2,6-disulfonate (AQDS). The genome of T. potens was recently sequenced, and the abundance of multiheme c-type cytochromes (MHCs) is unusual for a Gram-positive bacterium. We present evidence from trypsin shaving LC-MS/MS experiments and surface-enhanced Raman spectroscopy (SERS) that indicates the expression of a number of MHCs during T. potens growth on either HFO or AQDS and that several MHCs are localized to the cell wall or cell surface of T. potens. Furthermore, one of the MHCs can be extracted from cells with low pH or denaturants suggesting a loose association with the cell wall or cell surface. Electron microscopy does not reveal an S-layer, and the precipitation of silver metal on the cell surface is inhibited by cyanide, supporting the involvement of surface-localized redox-active heme proteins in dissimilatory metal reduction. These results are the first direct evidence for cell-wall associated cytochromes and MHC involvement in conducting electrons across the cell envelope of a Gram-positive bacterium.

A nanoporous metal recuperated MnO2 anode for lithium ion batteries.

PubMed

Guo, Xianwei; Han, Jiuhui; Zhang, Ling; Liu, Pan; Hirata, Akihiko; Chen, Luyang; Fujita, Takeshi; Chen, Mingwei

2015-10-07

Lithium-ion batteries (LIBs) have been intensively studied to meet the increased demands for the high energy density of portable electronics and electric vehicles. The low specific capacity of the conventional graphite based anodes is one of the key factors that limit the capacity of LIBs. Transition metal oxides, such as NiO, MnO2 and Fe3O4, are known to be promising anode materials that are expected to improve the specific capacities of LIBs for several times. However, the poor electrical conductivity of these oxides significantly restricts the lithium ion storage and charge/discharge rate. Here we report that dealloyed nanoporous metals can realize the intrinsic lithium storage performance of the oxides by forming oxide/metal composites. Without any organic binder, conductive additive and additional current collector, the hybrid electrodes can be directly used as anodes and show highly reversible specific capacity with high-rate capability and long cyclic stability.

Reversible control of magnetism in La 0.67Sr 0.33MnO 3 through chemically-induced oxygen migration

DOE PAGES

Grutter, A. J.; Gilbert, D. A.; Alaan, U. S.; ...

2016-02-22

We demonstrate reversible control of magnetization and anisotropy in La 0.67Sr 0.33MnO 3 films through interfacial oxygen migration. Gd metal capping layers deposited onto La 0.67Sr 0.33MnO 3 leach oxygen from the film through a solid-state redox reaction to form porous Gd 2O 3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Effects of the oxygen migration are observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive diffusion of oxygen vacancies. After Gd-capped Lamore » 0.67Sr 0.33MnO 3 is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd 2O 3 layer and the magnetization of the La 0.67Sr 0.33MnO 3 returns to the uncapped value. In conclusion, these findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.« less

Dissimilatory reduction and transformation of ferrihydrite-humic acid coprecipitates.

PubMed

Shimizu, Masayuki; Zhou, Jihai; Schröder, Christian; Obst, Martin; Kappler, Andreas; Borch, Thomas

2013-01-01

Organic matter (OM) is present in most terrestrial environments and is often found coprecipitated with ferrihydrite (Fh). Sorption or coprecipitation of OM with Fe oxides has been proposed to be an important mechanism for long-term C preservation. However, little is known about the impact of coprecipitated OM on reductive dissolution and transformation of Fe(III) (oxyhydr)oxides. Thus, we study the effect of humic acid (HA) coprecipitation on Fh reduction and secondary mineral formation by the dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens strain CN32. Despite similar crystal structure for all coprecipitates investigated, resembling 2-line Fh, the presence of coprecipitated HA resulted in lower specific surface areas. In terms of reactivity, coprecipitated HA resulted in slower Fh bioreduction rates at low C/Fe ratios (i.e., C/Fe ≤ 0.8), while high C/Fe ratios (i.e., C/Fe ≥ 1.8) enhanced the extent of bioreduction compared to pure Fh. The coprecipitated HA also altered the secondary Fe mineralization pathway by inhibiting goethite formation, reducing the amount of magnetite formation, and increasing the formation of a green rust-like phase. This study indicates that coprecipitated OM may influence the rates, pathway, and mineralogy of biogeochemical Fe cycling and anaerobic Fe respiration within soils.

Nitrogen-limited mangrove ecosystems conserve N through dissimilatory nitrate reduction to ammonium

PubMed Central

Fernandes, Sheryl Oliveira; Bonin, Patricia C.; Michotey, Valérie D.; Garcia, Nicole; LokaBharathi, P. A.

2012-01-01

Earlier observations in mangrove sediments of Goa, India have shown denitrification to be a major pathway for N loss1. However, percentage of total nitrate transformed through complete denitrification accounted for <0–72% of the pore water nitrate reduced. Here, we show that up to 99% of nitrate removal in mangrove sediments is routed through dissimilatory nitrate reduction to ammonium (DNRA). The DNRA process was 2x higher at the relatively pristine site Tuvem compared to the anthropogenically-influenced Divar mangrove ecosystem. In systems receiving low extraneous nutrient inputs, this mechanism effectively conserves and re-circulates N minimizing nutrient loss that would otherwise occur through denitrification. In a global context, the occurrence of DNRA in mangroves has important implications for maintaining N levels and sustaining ecosystem productivity. For the first time, this study also highlights the significance of DNRA in buffering the climate by modulating the production of the greenhouse gas nitrous oxide. PMID:22639727

Nitrogen-limited mangrove ecosystems conserve N through dissimilatory nitrate reduction to ammonium.

PubMed

Fernandes, Sheryl Oliveira; Bonin, Patricia C; Michotey, Valérie D; Garcia, Nicole; LokaBharathi, P A

2012-01-01

Earlier observations in mangrove sediments of Goa, India have shown denitrification to be a major pathway for N loss. However, percentage of total nitrate transformed through complete denitrification accounted for <0-72% of the pore water nitrate reduced. Here, we show that up to 99% of nitrate removal in mangrove sediments is routed through dissimilatory nitrate reduction to ammonium (DNRA). The DNRA process was 2x higher at the relatively pristine site Tuvem compared to the anthropogenically-influenced Divar mangrove ecosystem. In systems receiving low extraneous nutrient inputs, this mechanism effectively conserves and re-circulates N minimizing nutrient loss that would otherwise occur through denitrification. In a global context, the occurrence of DNRA in mangroves has important implications for maintaining N levels and sustaining ecosystem productivity. For the first time, this study also highlights the significance of DNRA in buffering the climate by modulating the production of the greenhouse gas nitrous oxide.

Morphology and phase identification of micron to nanosized manganese oxide (MnO) with variations in sintering time

NASA Astrophysics Data System (ADS)

Sasongko, Muhammad Ilman Nur; Puspitasari, Poppy; Yazirin, Cepi; Tsamroh, Dewi Izzatus; Risdanareni, Puput

2017-09-01

Manganese oxide (MnO) occurs in many rock types and may take the form of minerals. MnO has its drawbacks, namely highly reactive oxidizing species classified as dangerous and explosive at temperatures above 55 °C. Despite this,MnO has excellent magnetic, electrochemical, and conductivity properties, which should be reduced to nano-size to maximize their use and improve the properties of MnO. Phase and morphology characterization of powder this research aims to reduce the grain size of the MnO from micro to nano using the sol-gel method with various sintering times. Sol-gel is a simple synthesis method that has been proven capable of synthesizing a wide variety of micro-sized oxide materials into nano. Sintering time is a technique performed in the synthesis process to dry the material to a temperature above the normal temperature. The temperature used for sintering starting from 600 °C to 1000 °C. Characterizations were done using XRD, SEM, EDX, and FTIR machines. The sintering processes in this study used a temperature of 600 °C with different sintering periods of 30, 60 and 90 minutes. The XRD characterization with a 30-minute sintering time resulted in the smallest MnO in the form crystalline powder of 47.3 nm. The highest intensity (degree of crystallinity) found in MnO sintered for 90 minutes. The results of the morphological characterization of SEM showed a morphological change in MnO from micro-sized triangular to nano-sized spherical shape. The EDX characterization results indicated that the 30-minute sintering caused the lowest change in Mn and the highest change in O. The results of FTIR characterization showed a shift in C-H and Mn-O followed by an increase in the group of N-H, C=O and Mn-O.

Performance of MnO2 Crystallographic Phases in Rechargeable Lithium-Air Oxygen Cathode

NASA Astrophysics Data System (ADS)

Oloniyo, Olubukun; Kumar, Senthil; Scott, Keith

2012-05-01

Manganese dioxide (MnO2) has been shown to be effective for improving the efficiency of cathodes in lithium-air cells. Different crystallographic phases including α-, β-, and γ-MnO2 nanowires, α-MnO2 nanospheres, and α-MnO2 nanowires on carbon ( α-MnO2/C) were synthesized using the hydrothermal method. Their physical properties were examined using x-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurements, and scanning electron microscopy (SEM) and found to be in agreement with the literature. Electrochemical properties of the synthesized catalyst particles were investigated by fabricating cathodes and testing them in a lithium-air cell with lithium hexafluorophosphate in propylene carbonate (LiPF6/PC) and tetra(ethylene glycol)dimethyl ether (LiTFSi/TEGDME) electrolytes. α-MnO2 had the highest discharge capacity in the LiTFSi/TEGDME electrolyte (2500 mAh/g), whilst α-MnO2/C in LiPF6/PC showed a significantly higher discharge capacity of 11,000 mAh/g based on total mass of the catalytic cathode. However, the latter showed poor capacity retention compared with γ-MnO2 nanowires, which was stable for up to 30 cycles. The reported discharge capacity is higher than recorded in previous studies on lithium-air cells.

Selective interlayer ferromagnetic coupling between the Cu spins in YBa2Cu3O7−x grown on top of La0.7Ca0.3MnO3

PubMed Central

Huang, S. W.; Wray, L. Andrew; Jeng, Horng-Tay; Tra, V. T.; Lee, J. M.; Langner, M. C.; Chen, J. M.; Roy, S.; Chu, Y. H.; Schoenlein, R. W.; Chuang, Y.-D.; Lin, J.-Y.

2015-01-01

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa2Cu3O7−x (YBCO) superconductor when it is grown on top of ferromagnetic La0.7Ca0.3MnO3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO2 but not with La0.7Ca0.3O interfacial termination. Such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO2 plane at the La0.7Ca0.3O and MnO2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems. PMID:26573394

Mineral transformations during the dissolution of uranium ore minerals by dissimilatory metal-reducing bacteria

NASA Astrophysics Data System (ADS)

Glasauer, S.; Weidler, P.; Fakra, S.; Tyliszczak, T.; Shuh, D.

2011-12-01

Carnotite minerals [X2(UO2)2(VO4)2]; X = K, Ca, Ba, Mn, Na, Cu or Pb] form the major ore of uranium in the Colorado Plateau. These deposits are highly oxidized and contain U(VI) and V(IV). The biotransformation of U(VI) bound in carnotite by bacteria during dissimilatory metal reduction presents a complex puzzle in mineral chemistry. Both U(VI) and V(V) can be respired by metal reducing bacteria, and the mineral structure can change depending on the associated counterion. We incubated anaerobic cultures of S. putrefaciens CN32 with natural carnotite minerals from southeastern Utah in a nutrient-limited defined medium. Strain CN32 is a gram negative bacterium and a terrestrial isolate from New Mexico. The mineral and metal transformations were compared to a system that contained similar concentrations of soluble U(VI) and V(V). Electron (SEM, TEM) microscopies and x-ray spectromicroscopy (STXM) were used in conjunction with XRD to track mineral changes, and bacterial survival was monitored throughout the incubations. Slow rates of metal reduction over 10 months for the treatment with carnotite minerals revealed distinct biotic and abiotic processes, providing insight on mineral transformation and bacteria-metal interactions. The bacteria existed as small flocs or individual cells attached to the mineral phase, but did not adsorb soluble U or V, and accumulated very little of the biominerals. Reduction of mineral V(V) necessarily led to a dismantling of the carnotite structure. Bioreduction of V(V) by CN32 contributed small but profound changes to the mineral system, resulting in new minerals. Abiotic cation exchange within the carnotite group minerals induced the rearrangement of the mineral structures, leading to further mineral transformation. In contrast, bacteria survival was poor for treatments with soluble U(VI) and V(V), although both metals were reduced completely and formed solid UO2 and VO2; we also detected V(III). For these treatments, the bacteria

Effect of Al and Mg Contents on Wettability and Reactivity of Molten Zn-Al-Mg Alloys on Steel Sheets Covered with MnO and SiO2 Layers

NASA Astrophysics Data System (ADS)

Huh, Joo-Youl; Hwang, Min-Je; Shim, Seung-Woo; Kim, Tae-Chul; Kim, Jong-Sang

2018-05-01

The reactive wetting behaviors of molten Zn-Al-Mg alloys on MnO- and amorphous (a-) SiO2-covered steel sheets were investigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests were carried out at 460 °C and the variation in the contact angles (θc) of alloys containing 0.2-2.5 wt% Al and 0-3.0 wt% Mg was monitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the a-SiO2-covered steel exhibited nonreactive, nonwetting (θc > 90°) behavior. The MnO layer was rapidly removed by Al and Mg contained in the alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreased upon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the a-SiO2 layer were found to be sluggish, the wettability of Zn-Al-Mg alloys on the a-SiO2 layer improved upon increasing the Al and Mg contents. These results suggest that the wetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and SiO2, with Zn-Al-Mg alloys could be most effectively improved by increasing the Mg content of the alloys.

Intrinsic quantum spin Hall and anomalous Hall effects in h-Sb/Bi epitaxial growth on a ferromagnetic MnO2 thin film.

PubMed

Zhou, Jian; Sun, Qiang; Wang, Qian; Kawazoe, Yoshiyuki; Jena, Puru

2016-06-07

Exploring a two-dimensional intrinsic quantum spin Hall state with a large band gap as well as an anomalous Hall state in realizable materials is one of the most fundamental and important goals for future applications in spintronics, valleytronics, and quantum computing. Here, by combining first-principles calculations with a tight-binding model, we predict that Sb or Bi can epitaxially grow on a stable and ferromagnetic MnO2 thin film substrate, forming a flat honeycomb sheet. The flatness of Sb or Bi provides an opportunity for the existence of Dirac points in the Brillouin zone, with its position effectively tuned by surface hydrogenation. The Dirac points in spin up and spin down channels split due to the proximity effects induced by MnO2. In the presence of both intrinsic and Rashba spin-orbit coupling, we find two band gaps exhibiting a large band gap quantum spin Hall state and a nearly quantized anomalous Hall state which can be tuned by adjusting the Fermi level. Our findings provide an efficient way to realize both quantized intrinsic spin Hall conductivity and anomalous Hall conductivity in a single material.

Low frequency sonochemical synthesis of nanoporous amorphous manganese dioxide (MnO2) and adsorption of remazol reactive dye

NASA Astrophysics Data System (ADS)

Hasan, Siti Zubaidah; Yusop, Muhammad Rahimi; Othman, Mohamed Rozali

2015-09-01

Nanoporous amorphous-MnO2 was synthesized by sonochemical process (sonication) on the solid manganese (II) acetate tetrahydrate (Mn(CH3COO)2.4H2O) in 0.1 M KMnO4. The product was characterized by X-ray diffraction (XRD), morphology of the material was scanned by Field Emission Scanning Electron Microscopy (FE-SEM) and absorptions of MnO2 bonding was characterized by Fourier Transform Infra-Red Spectrometer (FT-IR). Remazol reactive dye or Red 3BS, was used in the adsorption study using nanoporous amorphous-MnO2. In batch experiment, 10 ppm of Remazol reactive dye was used and experiment was carried out at room temperature. Adsorption of Remazol dye on 0.2g synthesized nanoporous amorphous-MnO2 showed 99 - 100% decolorization.

Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium

USGS Publications Warehouse

Sparks, N.H.C.; Mann, S.; Bazylinski, D.A.; Lovley, D.R.; Jannasch, H.W.; Frankel, R.B.

1990-01-01

Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57Fe Mo??ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 ?? 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of {110} faces which are capped and truncated by {111} end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization. ?? 1990.

Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery

PubMed Central

Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

2016-01-01

α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm−2. At 1.0 V of cell voltage, a current density of 324 mA cm−2 is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm−2, and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte. PMID:27646032

Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery.

PubMed

Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

2016-09-20

α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm(-2). At 1.0 V of cell voltage, a current density of 324 mA cm(-2) is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm(-2), and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte.

Influence of an O2 background gas on the composition and kinetic energies of species in laser induced La0.4Ca0.6MnO3 plasmas

NASA Astrophysics Data System (ADS)

Chen, Jikun; Stender, Dieter; Bator, Matthias; Schneider, Christof W.; Lippert, Thomas; Wokaun, Alexander

2013-08-01

Oxygen is one of the most commonly used background gases for pulsed laser deposition of oxide thin films. In this work the properties of a 308 nm laser-induced La0.4Ca0.6MnO3 plasma were analyzed using a quadrupole mass spectrometer combined with an energy analyzer, to investigate the interaction between the various plasma species and the background gas. The composition and kinetic energies of the plasma species were compared in vacuum and an O2 background gas at different pressures. It has been observed that the O2 background gas decreases the kinetic energy of the positively charged atomic plasma species. In addition, the interaction with the O2 background gas causes the generation of positive diatomic oxide species of LaO+, CaO+ and MnO+. The amount of negatively charged diatomic or tri-atomic oxide species decreases in the O2 background compared to vacuum, while the amount of O2- increases strongly.

Effects of Electrodeposition Mode and Deposition Cycle on the Electrochemical Performance of MnO2-NiO Composite Electrodes for High-Energy-Density Supercapacitors.

PubMed

Rusi; Majid, S R

2016-01-01

Nanostructured network-like MnO2-NiO composite electrodes were electrodeposited onto stainless steel substrates via different electrodeposition modes, such as chronopotentiometry, chronoamperometry, and cyclic voltammetry, and then subjected to heat treatment at 300°C for metal oxide conversion. X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy were used to study the crystalline natures and morphologies of the deposited films. The electrochemical properties were investigated using cyclic voltammetry and charge/discharge tests. The results revealed that the electrochemical performance of the as-obtained composite electrodes depended on the electrodeposition mode. The electrochemical properties of MnO2-NiO composite electrodes prepared using cyclic voltammetry exhibited the highest capacitance values and were most influenced by the deposition cycle number. The optimum specific capacitance was 3509 Fg-1 with energy and power densities of 1322 Wh kg-1 and 110.5 kW kg-1, respectively, at a current density of 20 Ag-1 in a mixed KOH/K3Fe(CN)6 electrolyte.

Effects of Electrodeposition Mode and Deposition Cycle on the Electrochemical Performance of MnO2-NiO Composite Electrodes for High-Energy-Density Supercapacitors

PubMed Central

Rusi; Majid, S. R.

2016-01-01

Nanostructured network-like MnO2-NiO composite electrodes were electrodeposited onto stainless steel substrates via different electrodeposition modes, such as chronopotentiometry, chronoamperometry, and cyclic voltammetry, and then subjected to heat treatment at 300°C for metal oxide conversion. X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy were used to study the crystalline natures and morphologies of the deposited films. The electrochemical properties were investigated using cyclic voltammetry and charge/discharge tests. The results revealed that the electrochemical performance of the as-obtained composite electrodes depended on the electrodeposition mode. The electrochemical properties of MnO2-NiO composite electrodes prepared using cyclic voltammetry exhibited the highest capacitance values and were most influenced by the deposition cycle number. The optimum specific capacitance was 3509 Fg−1 with energy and power densities of 1322 Wh kg−1 and 110.5 kW kg−1, respectively, at a current density of 20 Ag−1 in a mixed KOH/K3Fe(CN)6 electrolyte. PMID:27182595

The effects of high magnetic field on the morphology and microwave electromagnetic properties of MnO 2 powder

NASA Astrophysics Data System (ADS)

Zhang, Jia; Yuping, Duan; Shuqing, Li; Xiaogang, Li; Shunhua, Liu

2010-07-01

MnO 2 with a sea urchin-like ball chain shape was first synthesized in a high magnetic field via a simple chemical process, and a mechanism for the formation of this grain shape was discussed. The as-synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The dielectric constant and the loss tangent clearly decreased under a magnetic field. The magnetic loss tangent and the imaginary part of the magnetic permeability increased substantially. Furthermore, the theoretically calculated values of reflection loss showed that the absorption peaks shifted to a higher frequency with increases in the magnetic field strength.

Flexible solid-state symmetric supercapacitors based on MnO2 nanofilms with high rate capability and long cyclability

NASA Astrophysics Data System (ADS)

Wu, Lingxia; Li, Ruizhi; Guo, Junling; Zhou, Cheng; Zhang, Wenpei; Wang, Chong; Huang, Yu; Li, Yuanyuan; Liu, Jinping

2013-08-01

Flexible solid-state symmetric supercapacitor was fabricated using MnO2 nanofilms growing directly on carbon cloth as the electrodes and PVA/H3PO4 gel as the electrolyte/separator. The device can be operated at a stable cell-voltage up to 1.4 V, obviously larger than that of conventional solid-state symmetric supercapacitors (≤1 V). It exhibited excellent rate capability with a scan rate as high as 20 V s-1 and a long cyclability (˜60000 cycles) even under severe mechanical deformation. The charge storage mechanism at different scan rates was also quantitatively analyzed.

Selective interlayer ferromagnetic coupling between the Cu spins in YBa 2Cu 3O 7–x grown on top of La 0.7Ca 0.3MnO 3

DOE PAGES

Huang, S. W.; Wray, L. Andrew; Jeng, Horng -Tay; ...

2015-11-17

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa 2Cu 3O 7–x (YBCO) superconductor when it is grown on top of ferromagnetic La 0.7Ca 0.3MnO 3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO 2 but not withmore » La 0.7Ca 0.3O interfacial termination. Thus, such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO 2 plane at the La 0.7Ca 0.3O and MnO 2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.« less

Thermal Decomposition Behaviors and Burning Characteristics of AN/RDX-Based Composite Propellants Supplemented with MnO2 and Fe2O3

NASA Astrophysics Data System (ADS)

Kohga, Makoto; Naya, Tomoki

2015-10-01

Ammonium nitrate (AN)-based composite propellants have gained popularity because of the clean burning nature of AN as an oxidizer. However, such propellants have several disadvantages such as poor ignition and low burning rate. The burning characteristics of the AN propellant were improved when a portion of this propellant was replaced by an energetic material and the addition of a catalyst. In this study, RDX (1,3,5-trinitroperhydro-1,3,5-triazine) was used as the energetic material, and Fe2O3 and MnO2 were used as catalysts. The burning characteristics of the AN/RDX propellants supplemented with catalysts were investigated, and the effects of the replacement of AN by RDX and the catalyst addition were evaluated.

Preparation and characterization of Ba0.2Sr0.2La0.6MnO3 nanoparticles and investigation of size & shape effect on microwave absorption

NASA Astrophysics Data System (ADS)

Peymanfar, Reza; Javanshir, Shahrzad

2017-06-01

In this paper, the design and characterization of a radar absorbing material (RAM) was investigated at microwave frequency. Ba0.2Sr0.2La0.6MnO3 magnetic nanoparticles was synthesized thru a facile hydrothermal method in the presence of polymethyl methacrylate (PMMA) and the possibility of shape and size-controlled synthesis of nanoparticles (NPs) over the range 15-50 Nm was also explored. Afterward, the effect of shape and size of the synthesized Ba0.2Sr0.2La0.6MnO3 NPs on microwave absorption properties was investigated in KU-band. The crystal structures and morphology of as-synthesized nanoparticles were characterized and confirmed by FESEM, XRD, VSM, FTIR analysis. The RAM samples were prepared by dispersion of magnetic NPs in silicone rubber in an ultrasonic bath. The maximum reflection loss (RL) values NPs were 12.04 dB at 14.82 GHz and a broad absorption band (over 1.22 GHz) with RL values <-10 dB are obtained and the maximum reflection loss (RL) values of decrease and shaped NPs were 22.36 dB at 14.78 GHz and a broad absorption band (over 2.67 GHz) with RL values <-10 dB are obtained. The results indicated that the particle size and shape play a major role on the absorption properties of the composites in the 12.4-18 GHz frequency range. It is observed that microwave absorption properties increased with the decrease in average particle size of NPs.

Increased Curie Temperature Induced by Orbital Ordering in La0.67Sr0.33MnO3/BaTiO3 Superlattices.

PubMed

Zhang, Fei; Wu, Biao; Zhou, Guowei; Quan, Zhi-Yong; Xu, Xiao-Hong

2018-01-17

Recent theoretical studies indicated that the Curie temperature of perovskite manganite thin films can be increased by more than an order of magnitude by applying appropriate interfacial strain to control orbital ordering. In this work, we demonstrate that the regular intercalation of BaTiO 3 layers between La 0.67 Sr 0.33 MnO 3 layers effectively enhances ferromagnetic order and increases the Curie temperature of La 0.67 Sr 0.33 MnO 3 /BaTiO 3 superlattices. The preferential orbital occupancy of e g (x 2 -y 2 ) in La 0.67 Sr 0.33 MnO 3 layers induced by the tensile strain of BaTiO 3 layers is identified by X-ray linear dichroism measurements. Our results reveal that controlling orbital ordering can effectively improve the Curie temperature of La 0.67 Sr 0.33 MnO 3 films and that in-plane orbital occupancy is beneficial to the double exchange ferromagnetic coupling of thin-film samples. These findings create new opportunities for the design and control of magnetism in artificial structures and pave the way to a variety of novel magnetoelectronic applications that operate far above room temperature.

Dissimilatory Reduction of Extracellular Electron Acceptors in Anaerobic Respiration

PubMed Central

Richter, Katrin; Schicklberger, Marcus

2012-01-01

An extension of the respiratory chain to the cell surface is necessary to reduce extracellular electron acceptors like ferric iron or manganese oxides. In the past few years, more and more compounds were revealed to be reduced at the surface of the outer membrane of Gram-negative bacteria, and the list does not seem to have an end so far. Shewanella as well as Geobacter strains are model organisms to discover the biochemistry that enables the dissimilatory reduction of extracellular electron acceptors. In both cases, c-type cytochromes are essential electron-transferring proteins. They make the journey of respiratory electrons from the cytoplasmic membrane through periplasm and over the outer membrane possible. Outer membrane cytochromes have the ability to catalyze the last step of the respiratory chains. Still, recent discoveries provided evidence that they are accompanied by further factors that allow or at least facilitate extracellular reduction. This review gives a condensed overview of our current knowledge of extracellular respiration, highlights recent discoveries, and discusses critically the influence of different strategies for terminal electron transfer reactions. PMID:22179232

Role of Humic-Bound Iron as an Electron Transfer Agent in Dissimilatory Fe(III) Reduction

PubMed Central

Lovley, Derek R.; Blunt-Harris, Elizabeth L.

1999-01-01

The dissimilatory Fe(III) reducer Geobacter metallireducens reduced Fe(III) bound in humic substances, but the concentrations of Fe(III) in a wide range of highly purified humic substances were too low to account for a significant portion of the electron-accepting capacities of the humic substances. Furthermore, once reduced, the iron in humic substances could not transfer electrons to Fe(III) oxide. These results suggest that other electron-accepting moieties in humic substances, such as quinones, are the important electron-accepting and shuttling agents under Fe(III)-reducing conditions. PMID:10473447

The phase structure and electrochemical performance of xLi2MnO3·(1 - x)LiNi1/3Co1/3Mn1/3O2 during the synthesis and charge-discharge process

NASA Astrophysics Data System (ADS)

Yuan, Ting; Liu, HongQuan; Gu, YiJie; Cui, HongZhi; Wang, YanMin

2016-09-01

The lithium-rich layered xLi2MnO3·(1 - x)LiNi1/3Co1/3Mn1/3O2 materials were simply prepared by the molten-salt method. The effects of reaction temperature and x value on the phase structure and electrochemistry were systemically studied by X-ray diffraction, galvanostatical charge/discharge and electrochemical impedance spectroscopy (EIS). It has been found that the obtained phase is sensitive to the reaction temperature and composition. A layered rock-salt form with hexagonal α-NaFeO2-type structure occurs at 700 °C, while a spinel LiMn2O4 becomes the main phase at 800 °C. Besides, a spinel Li4Mn5O12 component can be found in the lithium-rich layered material when x value decreases to 0.4. The 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 material can deliver a high initial discharge capacity of 218 mAhg-1 under 20 mAg-1 current rate, then increase to the maximum 241 mAhg-1 after 4 cycles. It is confirmed by different cycle d Q/d V profile change that the layer rock-salt transforms into the two phases with the layer rock-salt phase and the spinel phase step by step. According to the EIS analysis, the 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 sample with the better electrochemical performance shows the smaller charge transfer resistance and Warburg impedance associated with Li-ion diffusion through cathode, which is attributed to contribution from a fast 3D Li-ion diffusion channel of appropriate Li4Mn5O12 phase.

MnO Nanoparticle@Mesoporous Carbon Composites Grown on Conducting Substrates Featuring High-performance Lithium-ion Battery, Supercapacitor and Sensor

PubMed Central

Wang, Tianyu; Peng, Zheng; Wang, Yuhang; Tang, Jing; Zheng, Gengfeng

2013-01-01

We demonstrate a facile, two-step coating/calcination approach to grow a uniform MnO nanoparticle@mesoporous carbon (MnO@C) composite on conducting substrates, by direct coating of the Mn-oleate precursor solution without any conducting/binding reagents, and subsequent thermal calcination. The monodispersed, sub-10 nm MnO nanoparticles offer high theoretical energy storage capacities and catalytic properties, and the mesoporous carbon coating allows for enhanced electrolyte transport and charge transfer towards/from MnO surface. In addition, the direct growth and attachment of the MnO@C nanocomposite in the supporting conductive substrates provide much reduced contact resistances and efficient charge transfer. These excellent features allow the use of MnO@C nanocomposites as lithium-ion battery and supercapacitor electrodes for energy storage, with high reversible capacity at large current densities, as well as excellent cycling and mechanical stabilities. Moreover, this MnO@C nanocomposite has also demonstrated a high sensitivity for H2O2 detection, and also exhibited attractive potential for the tumor cell analysis. PMID:24045767

Growth and electrical transport properties of La 0.7 Sr 0.3 MnO 3 thin films on Sr 2 IrO 4 single crystals

DOE PAGES

Moon, E. J.; May, A. F.; Shafer, P.; ...

2017-04-20

Here, we report the physical properties of La 0.7 Sr 0.3 MnO 3 thin films on Sr 2 IrO 4 single crystals. We also deposited the manganite films using oxide molecular beam epitaxy on flux-grown (001)-oriented iridate crystals. Temperature-dependent magnetotransport and x-ray magnetic circular dichroism measurements reveal the presence of a ferromagnetic metallic ground state in the films, consistent with films grown on SrTiO 3 and La 0.3 Sr 0.7 Al 0.65 Ta 0.35 O 3 . A parallel resistance model is used to separate conduction effects within the Sr 2 IrO 4 substrate and the La 0.7 Sr 0.3more » MnO 3 thin films, revealing that the measured resistance maximum does not correspond to the manganite Curie temperature but results from a convolution of properties of the near-insulating substrate and metallic film. Furthermore, the ability to grow and characterize epitaxial perovskites on Sr 2 IrO 4 crystals enables a new route for studying magnetism at oxide interfaces in the presence of strong spin-orbit interactions.« less

Effect of MnO content on the interfacial property of mold flux and steel

NASA Astrophysics Data System (ADS)

Wang, Wanlin; Li, Jingwen; Zhou, Lejun; Yang, Jian

2016-07-01

The interfacial property between liquid mold flux and steel has significant impact on the quality of casting slab, and this property is mainly determined by the chemical composition of mold flux and the reaction between the flux and steel. The effect of MnO content on the contact angle and interfacial tension between liquid mold flux and ultra-low carbon steel was investigated by sessile drop method in this article, and the results suggested that both the contact angle and interfacial tension decreased with the increase of MnO content in the mold flux. The increase of Si and Mn and the reduction of Al and Ti in the interaction layer were caused by the chemical reactions occurred in the vicinity of interface between mold flux and steel substrate. Besides, the thickness of the interaction layer increased from 4 μm to 7 μm, then to 9 μm, 11 μm and 15 μm when the MnO content was added from 1 wt% to 3 wt%, then to 5 wt%, 7 wt%, and 9 wt% due to the fact that MnO can simplify the polymerized structure of the melt and improve the penetrability of molten mold flux to make the interfacial reaction easier.

Concurrent ionic migration and electronic effects at the memristive TiO x /La1/3Ca2/3MnO3-x interface

NASA Astrophysics Data System (ADS)

Román Acevedo, W.; Ferreyra, C.; Sánchez, M. J.; Acha, C.; Gay, R.; Rubi, D.

2018-03-01

The development of reliable redox-based resistive random-access memory devices requires understanding and disentangling concurrent effects present at memristive interfaces. We report on the fabrication and electrical characterization of TiO x /La1/3Ca2/3MnO3-x microstructured interfaces and on the modeling of their memristive behavior. We show that a careful tuning of the applied external electrical stimuli allows controlling the redox process between both layers, obtaining multilevel non-volatile resistance states. We simulate the oxygen vacancies dynamics at the interface between both oxides, and successfully reproduce the experimental electrical behavior after the inclusion of an electronic effect, related to the presence of an n-p diode at the interface. The formation of the diode is due to the n- and p-character of TiO x and La1/3Ca2/3MnO3-x , respectively. Our analysis indicates that oxygen vacancies migration between both layers is triggered after the diode is polarized either in forward mode or in reverse mode above breakdown. Electrical measurements at different temperatures suggest that the diode can be characterized as Zener-type. The advantages of our junctions for their implementation in RRAM devices are finally discussed.

Surveying N2O-producing pathways in bacteria.

PubMed

Stein, Lisa Y

2011-01-01

Nitrous oxide (N(2)O) is produced by bacteria as an intermediate of both dissimilatory and detoxification pathways under a range of oxygen levels, although the majority of N(2)O is released in suboxic to anoxic environments. N(2)O production under physiologically relevant conditions appears to require the reduction of nitric oxide (NO) produced from the oxidation of hydroxylamine (nitrification), reduction of nitrite (denitrification), or by host cells of pathogenic bacteria. In a single bacterial isolate, N(2)O-producing pathways can be complex, overlapping, involve multiple enzymes with the same function, and require multiple layers of regulatory machinery. This overview discusses how to identify known N(2)O-producing inventory and regulatory sequences within bacterial genome sequences and basic physiological approaches for investigating the function of that inventory. A multitude of review articles have been published on individual enzymes, pathways, regulation, and environmental significance of N(2)O-production encompassing a large diversity of bacterial isolates. The combination of next-generation deep sequencing platforms, emerging proteomics technologies, and basic microbial physiology can be used to expand what is known about N(2)O-producing pathways in individual bacterial species to discover novel inventory and unifying features of pathways. A combination of approaches is required to understand and generalize the function and control of N(2)O production across a range of temporal and spatial scales within natural and host environments. Copyright © 2011 Elsevier Inc. All rights reserved.

Electronic structure at transition metal phthalocyanine-transition metal oxide interfaces: Cobalt phthalocyanine on epitaxial MnO films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glaser, Mathias; Peisert, Heiko, E-mail: heiko.peisert@uni-tuebingen.de; Adler, Hilmar

2015-03-14

The electronic structure of the interface between cobalt phthalocyanine (CoPc) and epitaxially grown manganese oxide (MnO) thin films is studied by means of photoemission (PES) and X-ray absorption spectroscopy (XAS). Our results reveal a flat-lying adsorption geometry of the molecules on the oxide surface which allows a maximal interaction between the π-system and the substrate. A charge transfer from MnO, in particular, to the central metal atom of CoPc is observed by both PES and XAS. The change of the shape of N-K XAS spectra at the interface points, however, to the involvement of the Pc macrocycle in the chargemore » transfer process. As a consequence of the charge transfer, energetic shifts of MnO related core levels were observed, which are discussed in terms of a Fermi level shift in the semiconducting MnO films due to interface charge redistribution.« less

PREPARATION AND ELECTRICAL PROPERTIES OF BiFeO3/La0.7Sr0.3MnO3 MULTILAYERS

NASA Astrophysics Data System (ADS)

Zhu, Huiwen; Wang, Shunli; Li, Xiaoyun

2013-07-01

(La0.7Sr0.3MnO3 12 nm/BiFeO3 12 nm)10 was grown on SrTiO3 (001) substrate using rf magnetron sputtering. The structure analysis indicated that BiFeO3/La0.7Sr0.3MnO3 multilayers were highly (001)-oriented. Compared with bottom La0.7Sr0.3MnO3 electrode, the top La0.7Sr0.3MnO3 electrode displayed a rougher surface. The electric transport characteristics of the sample were investigated mainly at low temperature, and it was found that the sample exhibited resistance-temperature curves similar to those of La0.7Sr0.3MnO3 with the exception of an upturn at lower temperature region. Furthermore, a nonlinear I-V curve, which is characteristic of a tunneling conduction mechanism, was observed at 50 K. At higher temperature, the I-V curves were found to be diode-like. When the temperature was further increased to 300 K, the sample showed a space charge limited conduction (SCLC) characteristic.

Bacterial Diversity Across a Turbidite-Stranded Sediment-Water Interface, La Jolla Canyon, CA

NASA Astrophysics Data System (ADS)

Harrison, B. K.; Flood, B.; Myrbo, A.; Bailey, J.

2016-12-01

The emplacement of gravity-driven sediment flows imposes a significant physical and geochemical impact on underlying sediment and microbial communities. Although previous studies have established lasting mineralogical (e.g., McKay and Pederson, 2014) and biological signatures (e.g., Anschutz et al., 2002) of turbidite deposition, the response of prokaryotes within and beneath debris flows remains poorly constrained. Both bacterial cells associated with the underlying sediment and allocthonous material must respond to substantially altered selective pressures. As a consequence, turbidites and underlying sediments provide an exceptional opportunity to examine 1) microbial community response to sedimentation 2) preservation and identification of microbial dispersal mechanisms. We collected Illumina MiSeq sequence libraries across an intact marine turbidite boundary at 25cm sediment depth in La Jolla canyon off the coast of California. 16S rRNA gene signatures of relict and active bacterial populations exhibit persistent differences attributable to turbidite deposition. In particular, the sedimentary boundary is sharply demarcated at the cm scale by the diversity and abundance of Chloroflexi, Planctomycetes, and Actinobacteria. Variations in the abundance of putative dissimilatory sulfate-reducing Deltaproteobacteria across the stranded sediment-water interface reflect persistent turbidite-induced changes to the geochemical environment. This work raises the possibility that abrupt sedimentological events may alter the microbial community in a manner that persists with burial.

Charge ordered ferromagnetic phase in La_0.5Ca_0.5MnO_3

NASA Astrophysics Data System (ADS)

Mathur, Neil

2003-03-01

Charge order and ferromagnetism should be mutually exclusive in the manganites, because ferromagnetism in these materials is normally promoted by delocalised electrons. Surprisingly, a phase that is both strongly charge ordered and fully ferromagnetic is observed [1] at 90 K in La_0.5Ca_0.5MnO_3, using Fresnel imaging, dark-field TEM and electron holography. This new phase coexists with the two low temperature phases that were already known to coexist in La_0.5Ca_0.5MnO_3. (One of these expected phases is ferromagnetic but not charge-ordered, the other is charge-ordered but not ferromagnetic.) Strain fields could be responsible for the novel microscopic texture presented here - perhaps creating conditions in which nearest neighbour hopping is sufficient to promote ferromagnetism. Similarly, strain fields are believed to cause sub-micron phase separation in the manganites. It therefore seems that the manganites can adapt to their environments over a wide range of length scales [2]. [1] http://xxx.lanl.gov/abs/cond-mat/0209436 [2] Neil Mathur and Peter Littlewood, Physics Today, early 2003.

Redox states of Desulfovibrio vulgaris DsrC, a key protein in dissimilatory sulfite reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venceslau, Sofia S.; Cort, John R.; Baker, Erin Shammel

2013-11-29

Dissimilatory reduction of sulfite is carried out by the siroheme enzyme DsrAB, with the involvement of the protein DsrC having two conserved cysteine residues. Here, we report a study of the distribution of DsrC in cell extracts, a cysteine-labelling gel-shift assay to monitor its redox state and behaviour, and procedures to produce the different redox forms. We show that, in the model sulfate reducer Desulfovibrio vulgaris, the majority of DsrC is not associated with DsrAB and is thus free to interact with other proteins. In addition, we successfully produced DsrC with an intramolecular disulfide bond (oxidized state) by treatment withmore » arginine.« less

Redundancy and modularity in membrane-associated dissimilatory nitrate reduction in Bacillus

PubMed Central

Heylen, Kim; Keltjens, Jan

2012-01-01

The genomes of two phenotypically denitrifying type strains of the genus Bacillus were sequenced and the pathways for dissimilatory nitrate reduction were reconstructed. Results suggest that denitrification proceeds in the periplasmic space and in an analogous fashion as in Gram-negative organisms, yet with the participation of proteins that tend to be membrane-bound or membrane-associated. A considerable degree of functional redundancy was observed with marked differences between B. azotoformans LMG 9581T and B. bataviensis LMG 21833T. In addition to the already characterized menaquinol/cyt c-dependent nitric oxide reductase (Suharti et al., 2001, 2004) of which the encoding genes could be identified now, evidence for another novel nitric oxide reductase (NOR) was found. Also, our analyses confirm earlier findings on branched electron transfer with both menaquinol and cytochrome c as reductants. Quite unexpectedly, both bacilli have the disposal of two parallel pathways for nitrite reduction enabling a life style as a denitrifier and as an ammonifying bacterium. PMID:23087684

Towards a More Complete Picture: Dissimilatory Metal Reduction by Anaeromyxobacter Species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loeffler, Frank E.

2005-06-01

Towards a More Complete Picture: Dissimilatory Metal Reduction by Anaeromyxobacter Species The overarching goal of this 3-year project is to explore uranium reduction in Anaeromyxobacter species. Specifically, we explore the physiological requirements of available Anaeromyxobacter isolates, design molecular biology tools to detect and quantify Anaeromyxobacter in pure cultures, consortia, and environmental samples, assess their diversity, distribution, and abundance in the environment, including DOE sites, and attempt the isolation of additional Anaeromyxobacter species from the Oak Ridge Field Research Center (FRC). The performers on this project include Frank Loeffler (PI), Robert Sanford (Co-PI), Qingzhong Wu (postdoc), Sara Henry (graduate student withmore » fellowship, no charges to NABIR project), Ivy Thomson (graduate student, no charges to NABIR project), and Ryan Wagner (''Special Topics'' bioinformatics undergraduate student, no charges to NABIR project). Exploratory MALDI-TOF MS experiments for the specific detection of Anaeromyxobacter species were performed by Kerry Preston (graduate student, no charges to NABIR project).« less

Dissimilatory arsenate and sulfate reduction in sediments of two hypersaline, arsenic-rich soda lakes: Mono and Searles Lakes, California

USGS Publications Warehouse

Kulp, T.R.; Hoeft, S.E.; Miller, L.G.; Saltikov, C.; Murphy, J.N.; Han, S.; Lanoil, B.; Oremland, R.S.

2006-01-01

A radioisotope method was devised to study bacterial respiratory reduction of arsenate in sediments. The following two arsenic-rich soda lakes in California were chosen for comparison on the basis of their different salinities: Mono Lake (???90 g/liter) and Searles Lake (???340 g/liter). Profiles of arsenate reduction and sulfate reduction were constructed for both lakes. Reduction of [73As] arsenate occurred at all depth intervals in the cores from Mono Lake (rate constant [k] = 0.103 to 0.04 h-1) and Searles Lake (k = 0.012 to 0.002 h-1), and the highest activities occurred in the top sections of each core. In contrast, [35S] sulfate reduction was measurable in Mono Lake (k = 7.6 ?? 104 to 3.2 ?? 10-6 h-1) but not in Searles Lake. Sediment DNA was extracted, PCR amplified, and separated by denaturing gradient gel electrophoresis (DGGE) to obtain phylogenetic markers (i.e., 16S rRNA genes) and a partial functional gene for dissimilatory arsenate reduction (arrA). The amplified arrA gene product showed a similar trend in both lakes; the signal was strongest in surface sediments and decreased to undetectable levels deeper in the sediments. More arrA gene signal was observed in Mono Lake and was detectable at a greater depth, despite the higher arsenate reduction activity observed in Searles Lake. A partial sequence (about 900 bp) was obtained for a clone (SLAS-3) that matched the dominant DGGE band found in deeper parts of the Searles Lake sample (below 3 cm), and this clone was found to be closely related to SLAS-1, a novel extremophilic arsenate respirer previously cultivated from Searles Lake. Copyright ?? 2006, American Society for Microbiology. All Rights Reserved.

Three-Dimensional Fibrous Network of Na0.21 MnO2 for Aqueous Sodium-Ion Hybrid Supercapacitors.

PubMed

Karikalan, Natarajan; Karuppiah, Chelladurai; Chen, Shen-Ming; Velmurugan, Murugan; Gnanaprakasam, Periyasami

2017-02-16

Sodium-ion hybrid supercapacitors are potential energy-storage devices and have recently received enormous interest. However, the development of cathode materials and the use of nonaqueous electrolyte remain a great challenge. Hence, aqueous Na-ion hybrid supercapacitors based on a three-dimensional network of NaMnO 2 were developed. The cathode material was synthesized by the electro-oxidation of potassium manganese hexacyanoferrate nanocubes. The oxidized compound was confirmed to be Na 0.21 MnO 2 by various physical characterization methods. Manganese dioxide is a well-characterized material for aqueous asymmetric pseudocapacitors, but its usage at high operating voltages is limited due to the electrochemical stability of water. Nevertheless, high-potential and high-performance aqueous supercapacitors exhibiting a cell potential of 2.7 V were developed. Further, the practical applicability of an asymmetric supercapacitor based on NaMnO 2 (cathode) and reduced graphene oxide (anode) was demonstrated by powering a 2.1 V red LED. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanism of H2S Oxidation by the Dissimilatory Perchlorate-Reducing Microorganism Azospira suillum PS.

PubMed

Mehta-Kolte, Misha G; Loutey, Dana; Wang, Ouwei; Youngblut, Matthew D; Hubbard, Christopher G; Wetmore, Kelly M; Conrad, Mark E; Coates, John D

2017-02-21

The genetic and biochemical basis of perchlorate-dependent H 2 S oxidation (PSOX) was investigated in the dissimilatory perchlorate-reducing microorganism (DPRM) Azospira suillum PS (PS). Previously, it was shown that all known DPRMs innately oxidize H 2 S, producing elemental sulfur (S o ). Although the process involving PSOX is thermodynamically favorable ( ΔG °' = -206 kJ ⋅ mol -1 H 2 S), the underlying biochemical and genetic mechanisms are currently unknown. Interestingly, H 2 S is preferentially utilized over physiological electron donors such as lactate or acetate although no growth benefit is obtained from the metabolism. Here, we determined that PSOX is due to a combination of enzymatic and abiotic interactions involving reactive intermediates of perchlorate respiration. Using various approaches, including barcode analysis by sequencing (Bar-seq), transcriptome sequencing (RNA-seq), and proteomics, along with targeted mutagenesis and biochemical characterization, we identified all facets of PSOX in PS. In support of our proposed model, deletion of identified upregulated PS genes traditionally known to be involved in sulfur redox cycling (e.g., Sox, sulfide:quinone reductase [SQR]) showed no defect in PSOX activity. Proteomic analysis revealed differential abundances of a variety of stress response metal efflux pumps and divalent heavy-metal transporter proteins, suggesting a general toxicity response. Furthermore, in vitro biochemical studies demonstrated direct PSOX mediated by purified perchlorate reductase (PcrAB) in the absence of other electron transfer proteins. The results of these studies support a model in which H 2 S oxidation is mediated by electron transport chain short-circuiting in the periplasmic space where the PcrAB directly oxidizes H 2 S to S o The biogenically formed reactive intermediates (ClO 2 - and O 2 ) subsequently react with additional H 2 S, producing polysulfide and S o as end products. IMPORTANCE Inorganic sulfur

Electronic interaction in an outer-sphere mixed-valence double salt: a polarized neutron diffraction study of K(3)(MnO(4))(2).

PubMed

Cannon, Roderick D; Jayasooriya, Upali A; Tilford, Claire; Anson, Christopher E; Sowrey, Frank E; Rosseinsky, David R; Stride, John A; Tasset, Francis; Ressouche, Eric; White, Ross P; Ballou, Rafik

2004-11-01

The mixed-valence double salt K(3)(MnO(4))(2) crystallizes in space group P2(1)/m with Z = 2. The manganese centers Mn1 and Mn2 constitute discrete "permanganate", [Mn(VII)O(4)](-), and "manganate", [Mn(VI)O(4)](2-), ions, respectively. There is a spin-ordering transition to an antiferromagnetic state at ca. T = 5 K. The spin-density distribution in the paramagnetic phase at T = 10 K has been determined by polarized neutron diffraction, confirming that unpaired spin is largely confined to the nominal manganate ion Mn2. Through use of both Fourier refinement and maximum entropy methods, the spin on Mn1 is estimated as 1.75 +/- 1% of one unpaired electron with an upper limit of 2.5%.

Thermal properties of Pr2/3Sr1/3MnO3 manganites:PdO composites

NASA Astrophysics Data System (ADS)

Rao, Ashok; Manjunatha, S. O.; Bhatt, Ramesh Chandra; Awana, V. P. S.; Lin, C. F.; Kuo, Y. K.; Poornesh, P.

2017-10-01

In the present communication the results on thermal conductivity, Seebeck coefficient and specific heat of Pr2/3Sr1/3MnO3:PdO composites are reported. All the samples exhibit a pronounced anomaly in thermal conductivity (κ) at their respective Curie temperatures, TC of the samples. It is also observed that the overall magnitude of κ decreases with increasing Pd content. The observed reduction of the total k(T) is discussed with various thermal scattering mechanisms. The temperature-dependent Seebeck coefficient data S(T) in the high temperature region is analyzed within the framework of Mott's polaron hopping model. The analysis of low-temperature S(T) data reveals that the electron-magnon scattering contribution dominates the thermoelectric transport at low temperatures. The magnetic contribution for the CP and change in entropy (ΔS) during the magnetic phase transition is also evaluated.

Ultrathin two-dimensional MnO2/graphene hybrid nanostructures for high-performance, flexible planar supercapacitors.

PubMed

Peng, Lele; Peng, Xu; Liu, Borui; Wu, Changzheng; Xie, Yi; Yu, Guihua

2013-05-08

Planar supercapacitors have recently attracted much attention owing to their unique and advantageous design for 2D nanomaterials based energy storage devices. However, improving the electrochemical performance of planar supercapacitors still remains a great challenge. Here we report for the first time a novel, high-performance in-plane supercapacitor based on hybrid nanostructures of quasi-2D ultrathin MnO2/graphene nanosheets. Specifically, the planar structures based on the δ-MnO2 nanosheets integrated on graphene sheets not only introduce more electrochemically active surfaces for absorption/desorption of electrolyte ions, but also bring additional interfaces at the hybridized interlayer areas to facilitate charge transport during charging/discharging processes. The unique structural design for planar supercapacitors enables great performance enhancements compared to graphene-only devices, exhibiting high specific capacitances of 267 F/g at current density of 0.2 A/g and 208 F/g at 10 A/g and excellent rate capability and cycling stability with capacitance retention of 92% after 7000 charge/discharge cycles. Moreover, the high planar malleability of planar supercapacitors makes possible superior flexibility and robust cyclability, yielding capacitance retention over 90% after 1000 times of folding/unfolding. Ultrathin 2D nanomaterials represent a promising material platform to realize highly flexible planar energy storage devices as the power back-ups for stretchable/flexible electronic devices.

Dissimilatory nitrate reduction processes in sediments of urban river networks: Spatiotemporal variations and environmental implications.

PubMed

Cheng, Lv; Li, Xiaofei; Lin, Xianbiao; Hou, Lijun; Liu, Min; Li, Ye; Liu, Sai; Hu, Xiaoting

2016-12-01

Urbanizations have increased the loadings of reactive nitrogen in urban riverine environments. However, limited information about dissimilatory nitrate reduction processes and associated contributions to nitrogen removal is available for urban riverine environments. In this study, sediment slurry experiments were conducted with nitrogen isotope-tracing technique to investigate the potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) and their contributions to nitrate reduction in sediments of urban river networks, Shanghai. The potential rates of denitrification, anammox and DNRA measured in the study area ranged from 0.193 to 98.7 nmol N g -1  h -1 dry weight (dw), 0.0387-23.7 nmol N g -1  h -1  dw and 0-10.3 nmol N g -1  h -1  dw, respectively. Denitrification and DNRA rates were higher in summer than in winter, while anammox rates were greater in winter than in summer for most sites. Dissolved oxygen, total organic carbon, nitrate, ammonium, sulfide, Fe(II) and Fe(III) were found to have significant influence on these nitrate reduction processes. Denitrification contributed 11.5-99.5%% to total nitrate reduction, as compared to 0.343-81.6% for anammox and 0-52.3% for DNRA. It is estimated that nitrogen loss of approximately 1.33 × 10 5  t N year -1 was linked to both denitrification and anammox processes, which accounted for about 20.1% of total inorganic nitrogen transported annually into the urban river networks of Shanghai. Overall, these results show the potential importance of denitrification and anammox in nitrogen removal and provide new insight into the mechanisms of nitrogen cycles in urban riverine environments. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of gadolinium dopant on structural, magneto-transport, magnetic and thermo-power of Pr0.8Sr0.2MnO3

NASA Astrophysics Data System (ADS)

Poojary, Thrapthi; Babu, P. D.; Sanil, Tejaswini; Daivajna, Mamatha D.

2018-07-01

In the present investigation structural, magneto-transport, magnetic and thermo-power measurements of Gadolinium (Gd) doped Pr0.8-xGdxSr0.2MnO3 (0, 0.2, 0.25 and 0.3) manganites have been done. All the samples are single phased with orthorhombic structure. Temperature variation of resistance exhibits a high temperature transition occurring at 156 K and a low temperature cusp at around 95 K for pristine sample. With Gd doping resistance behavior shows insulating behavior throughout the whole temperature range. Magneto-Resistance (MR%) increases with Gd doping. A huge increase in thermo-electric power is observed with Gd doping.

Influence of MnO2 decorated Fe nano cauliflowers on microwave absorption and impedance matching of polyvinylbutyral (PVB) matrix

NASA Astrophysics Data System (ADS)

Bora, Pritom J.; Porwal, Mayuri; Vinoy, K. J.; Ramamurthy, Praveen C.; Madras, Giridhar

2016-09-01

In this work, a promising, polyvinyl butryl (PVB)-MnO2 decorated Fe composite was synthesised and microwave absorption properties were studied for the most important frequency ranges i.e., X-band (8.2-12.4 GHz) and Ku-band (12.4-18 GHz). The microwave absorption of Fe nano cauliflower structure can be enhanced by MnO2 nanofiber coating. 10 wt% Fe-MnO2 nano cauliflower loaded PVB composite films (2 mm thick) shows an appreciable increase in microwave absorption properties. In X-band, the reflection loss (RL) of this composite decreases almost linearly to -7.5 dB, whereas in the Ku-band the minimum RL was found to be -15.7 dB at 14.7 GHz. Here it was observed that impedance matching is the primarily important factor responsible for enhanced microwave absorption. Further, enhancement of EM attenuation constant (α), dielectrics, scattering attenuation also bolsters the obtained results. This polymer composite can be considered as a novel microwave absorbing coating material.

Na0.44MnO2 nanorods as a cathode material for Na-ion batteries

NASA Astrophysics Data System (ADS)

Avci, Sevda; Oz, Erdinc; Demirel, Serkan; Altin, Emine; Altin, Serdar; Bayri, Ali; Yakinci, Eyyuphan

2014-03-01

Lithium-ion batteries have dominated the rechargeable battery market because of their high energy and power capability. On the other hand, sodium is one of the more abundant elements on Earth unlike Li. Moreover, Na has similar chemical properties to Li, indicating that Na-ion batteries can be an alternative to Li counterparts. With that respect, we have synthesized Na0.44MnO2 nanorods as cathode materials for Na-ion batteries. We have investigated the effects of structural, electrical, and magnetic properties on battery performance. We report the synthesis conditions and growth mechanism of the nanorods. The structure and the morphology of the materials were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM) techniques. Temperature dependent structural changes were determined via in situ X-ray diffraction and TG-DTA measurements showing structural changes above room temperature. This work is funded by The Scientific and Technological Research Council of Turkey with Grant No:112M487.

Injectable Silica–Permanganate Gel as a Slow-Release MnO 4 - Source for Groundwater Remediation. Rheological Properties and Release Dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shuo; Oostrom, Martinus; Truex, Michael J.

2016-01-12

Injectable slow-release permanganate gel (ISRPG), formed by mixing KMnO 4 solution with fumed silica powder, may have a potential application in remediating chlorinated solvent plumes in groundwater. A series of batch, column, and flow cell experiments has been completed to test the gel behavior under a variety of conditions. The experiments have provided information on ISRPG rheology, permanganate (MnO 4 - ) release dynamics and distribution, and trichloroethene (TCE) degradation by ISRPG-released oxidant. The gel possesses remarkable shear thinning characteristics, resulting in a relative low viscosity during mixing, and facilitating its subsurface injection and distribution. Batch tests revealed that MnOmore » 4 - was diffused out from ISRPG into water while the gel did not dissolve or disperse into water but maintained its initial shape. Column experiments showed that MnO 4 - release from ISRPG lasted considerably longer than the release from aqueous solution. TCE degradation by ISRPG-released MnO 4 - was much more effective than that when MnO 4 - was delivered using aqueous solution injection. In two-dimensional flow cell experiments, it was demonstrated that ISRPG slowly released a long-lasting low concentration MnO 4 - plume sufficient for remediation and sustainable in an aquifer for a long period of time.« less

Enhancing Catalyzed Decomposition of Na2CO3 with Co2MnO x Nanowire-Decorated Carbon Fibers for Advanced Na-CO2 Batteries.

PubMed

Fang, Cong; Luo, Jianmin; Jin, Chengbin; Yuan, Huadong; Sheng, Ouwei; Huang, Hui; Gan, Yongping; Xia, Yang; Liang, Chu; Zhang, Jun; Zhang, Wenkui; Tao, Xinyong

2018-05-23

The metal-CO 2 batteries, especially Na-CO 2 , batteries come into sight owing to their high energy density, ability for CO 2 capture, and the abundance of sodium resource. Besides the sluggish electrochemical reactions at the gas cathodes and the instability of the electrolyte at a high voltage, the final discharge product Na 2 CO 3 is a solid and poor conductor of electricity, which may cause the high overpotential and poor cycle performance for the Na-CO 2 batteries. The promotion of decomposition of Na 2 CO 3 should be an efficient strategy to enhance the electrochemical performance. Here, we design a facile Na 2 CO 3 activation experiment to screen the efficient cathode catalyst for the Na-CO 2 batteries. It is found that the Co 2 MnO x nanowire-decorated carbon fibers (CMO@CF) can promote the Na 2 CO 3 decomposition at the lowest voltage among all these metal oxide-decorated carbon fiber structures. After assembling the Na-CO 2 batteries, the electrodes based on CMO@CF show lower overpotential and better cycling performance compared with the electrodes based on pristine carbon fibers and other metal oxide-modified carbon fibers. We believe this catalyst screening method and the freestanding structure of the CMO@CF electrode may provide an important reference for the development of advanced Na-CO 2 batteries.

Facile synthesis of a nitrogen-doped graphene flower-like MnO2 nanocomposite and its application in supercapacitors

NASA Astrophysics Data System (ADS)

Dong, Jinyang; Lu, Gang; Wu, Fan; Xu, Chenxi; Kang, Xiaohong; Cheng, Zhiming

2018-01-01

A flower-like MnO2 nanocomposite embedded in nitrogen-doped graphene (NG-MnO2) is fabricated by a hydrothermal method. It is a mesoporous nanomaterial with a pore size of approximately 0.765 cm3 g-1 and specific surface area of 201.8 m2 g-1. NG-MnO2 exhibits a superior average specific capacitance of 220 F g-1 at 0.5 A g-1 and a preferable capacitance of 189.1 F g-1, even at 10 A g-1. After 1000 cycles, over 98.3% of the original specific capacitance retention of the NG-MnO2 electrode is maintained, and it can even activate a red light emitting diode (LED) after being charged, which indicates that it has excellent cycling stability as an electrode material. This prominent electrochemical performance is primarily attributed to the nitrogen doping and mesoporous structures of NG-MnO2, which can be attributed to its numerous electroactive sites as well as faster ion and electron transfer for redox reactions than general graphene-MnO2 nanocomposites (G-MnO2).

The structural and electrical properties of polycrystalline La0.8Ca0.17Ag0.03MnO3 manganites

NASA Astrophysics Data System (ADS)

Ruli, F.; Kurniawan, B.; Imaduddin, A.

2018-04-01

In this paper, the authors report the electrical properties of polycrystalline La0.8Ca0.17Ag0.03MnO3 manganites synthesized using sol-gel method. The X-ray diffraction (XRD) patterns of polycrystalline La0.8Ca0.17Ag0.03MnO3 samples reveal an orthorhombic perovskite structure with Pnma space group. Analysis using energy dispersive X-ray (EDX) confirms that the sample contains all expected chemical elements without any additional impurity. The measurement of resistivity versus temperature using cryogenic magnetometer was performed to investigate the electrical properties. The results show that the electrical resistivity of polycrystalline La0.8Ca0.17Ag0.03MnO3 exhibits metalic behavior below 244 K. The temperature dependence of electrical resistivity dominantly emanates from electron-electron scattering and the grain/domain boundary play a important role in conduction mechanism in polycrystalline La0.8Ca0.17Ag0.03MnO3.

Potentiometric NO2 Sensors Based on Thin Stabilized Zirconia Electrolytes and Asymmetric (La0.8Sr0.2)0.95MnO3 Electrodes

PubMed Central

Zou, Jie; Zheng, Yangong; Li, Junliang; Zhan, Zhongliang; Jian, Jiawen

2015-01-01

Here we report on a new architecture for potentiometric NO2 sensors that features thin 8YSZ electrolytes sandwiched between two porous (La0.8Sr0.2)0.95MnO3 (LSM95) layers—one thick and the other thin—fabricated by the tape casting and co-firing techniques. Measurements of their sensing characteristics show that reducing the porosity of the supporting LSM95 reference electrodes can increase the response voltages. In the meanwhile, thin LSM95 layers perform better than Pt as the sensing electrode since the former can provide higher response voltages and better linear relationship between the sensitivities and the NO2 concentrations over 40–1000 ppm. The best linear coefficient can be as high as 0.99 with a sensitivity value of 52 mV/decade as obtained at 500 °C. Analysis of the sensing mechanism suggests that the gas phase reactions within the porous LSM95 layers are critically important in determining the response voltages. PMID:26205270

Three-Dimensional Ordered Mesoporous MnO2-Supported Ag Nanoparticles for Catalytic Removal of Formaldehyde.

PubMed

Bai, Bingyang; Qiao, Qi; Arandiyan, Hamidreza; Li, Junhua; Hao, Jiming

2016-03-01

Three-dimensional (3D) ordered mesoporous Ag/MnO2 catalyst was prepared by impregnation method based on 3D-MnO2 and used for catalytic oxidation of HCHO. Ag nanoparticles are uniformly distributed on the polycrystalline wall of 3D-MnO2. The addition of Ag does not change the 3D ordered mesoporous structure of the Ag/MnO2, but does reduce the pore size and surface area. Ag nanoparticles provide sufficient active site for the oxidation reaction of HCHO, and Ag (111) crystal facets in the Ag/MnO2 are active faces. The 8.9% Ag/MnO2 catalyst shows a higher normalized rate (10.1 nmol·s(-1)·m(-2) at 110 °C) and TOF (0.007 s(-1) at 110 °C) under 1300 ppm of HCHO and 150 000 h(-1) of GHSV, and its apparent activation energy of the reaction is the lowest (39.1 kJ/mol). More Ag active sites, higher low-temperature reducibility, more abundant surface lattice oxygen species, oxygen vacancies, and lattice defects generated from interaction Ag with MnO2 are responsible for the excellent catalytic performance of HCHO oxidation on the 8.9% Ag/MnO2 catalyst. The 8.9% Ag/MnO2 catalyst remained highly active and stable under space velocity increasing from 60 000 to 150 000 h(-1), under initial HCHO concentration increasing from 500 to 1300 ppm, and under the presence of humidity, respectively.

[Influence of MnO3 on Photoelectric Performance in Organic Light Emitting Diodes].

PubMed

Guan, Yun-xia; Chen, Li-jia; Chen, Ping; Fu, Xiao-qiang; Niu, Lian-bin

2016-03-01

550 and 2 035 cd x m(-2), respectively at 13 V. At 60 mA x cm(-2), the current efficiency of the microcavity OLEDs using MnO3 are about 2.2, 2.6, 3.1 and 2.6 cd x A(-2) respectively. It is found that electrons are majority carriers and holes are minority carriers in this microcavity OLEDs. MnO3 film can improve hole injection ability from 4 to 10 nm. In addition, hole injection ability is increased with the increasing thickness of the MnO3 film.

Phylogenetic analysis of dissimilatory Fe(III)-reducing bacteria

USGS Publications Warehouse

Lonergan, D.J.; Jenter, H.L.; Coates, J.D.; Phillips, E.J.P.; Schmidt, T.M.; Lovley, D.R.

1996-01-01

Evolutionary relationships among strictly anaerobic dissimilatory Fe(III)- reducing bacteria obtained from a diversity of sedimentary environments were examined by phylogenetic analysis of 16S rRNA gene sequences. Members of the genera Geobacter, Desulfuromonas, Pelobacter, and Desulfuromusa formed a monophyletic group within the delta subdivision of the class Proteobacteria. On the basis of their common ancestry and the shared ability to reduce Fe(III) and/or S0, we propose that this group be considered a single family, Geobacteraceae. Bootstrap analysis, characteristic nucleotides, and higher- order secondary structures support the division of Geobacteraceae into two subgroups, designated the Geobacter and Desulfuromonas clusters. The genus Desulfuromusa and Pelobacter acidigallici make up a distinct branch with the Desulfuromonas cluster. Several members of the family Geobacteraceae, none of which reduce sulfate, were found to contain the target sequences of probes that have been previously used to define the distribution of sulfate-reducing bacteria and sulfate-reducing bacterium-like microorganisms. The recent isolations of Fe(III)-reducing microorganisms distributed throughout the domain Bacteria suggest that development of 16S rRNA probes that would specifically target all Fe(III) reducers may not be feasible. However, all of the evidence suggests that if a 16S rRNA sequence falls within the family Geobacteraceae, then the organism has the capacity for Fe(III) reduction. The suggestion, based on geological evidence, that Fe(III) reduction was the first globally significant process for oxidizing organic matter back to carbon dioxide is consistent with the finding that acetate-oxidizing Fe(III) reducers are phylogenetically diverse.

Editable Supercapacitors with Customizable Stretchability Based on Mechanically Strengthened Ultralong MnO2 Nanowire Composite.

PubMed

Lv, Zhisheng; Luo, Yifei; Tang, Yuxin; Wei, Jiaqi; Zhu, Zhiqiang; Zhou, Xinran; Li, Wenlong; Zeng, Yi; Zhang, Wei; Zhang, Yanyan; Qi, Dianpeng; Pan, Shaowu; Loh, Xian Jun; Chen, Xiaodong

2018-01-01

Although some progress has been made on stretchable supercapacitors, traditional stretchable supercapacitors fabricated by predesigning structured electrodes for device assembling still lack the device-level editability and programmability. To adapt to wearable electronics with arbitrary configurations, it is highly desirable to develop editable supercapacitors that can be directly transferred into desirable shapes and stretchability. In this work, editable supercapacitors for customizable shapes and stretchability using electrodes based on mechanically strengthened ultralong MnO 2 nanowire composites are developed. A supercapacitor edited with honeycomb-like structure shows a specific capacitance of 227.2 mF cm -2 and can be stretched up to 500% without degradation of electrochemical performance, which is superior to most of the state-of-the-art stretchable supercapacitors. In addition, it maintains nearly 98% of the initial capacitance after 10 000 stretch-and-release cycles under 400% tensile strain. As a representative of concept for system integration, the editable supercapacitors are integrated with a strain sensor, and the system exhibits a stable sensing performance even under arm swing. Being highly stretchable, easily programmable, as well as connectable in series and parallel, an editable supercapacitor with customizable stretchability is promising to produce stylish energy storage devices to power various portable, stretchable, and wearable devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Detailed studies of a high-capacity electrode material for rechargeable batteries, Li2MnO3-LiCo(1/3)Ni(1/3)Mn(1/3)O2.

PubMed

Yabuuchi, Naoaki; Yoshii, Kazuhiro; Myung, Seung-Taek; Nakai, Izumi; Komaba, Shinichi

2011-03-30

Lithium-excess manganese layered oxides, which are commonly described by the chemical formula zLi(2)MnO(3)-(1-z)LiMeO(2) (Me = Co, Ni, Mn, etc.), are of great importance as positive electrode materials for rechargeable lithium batteries. In this Article, Li(x)Co(0.13)Ni(0.13)Mn(0.54)O(2-δ) samples are prepared from Li(1.2)Ni(0.13)Co(0.13)Mn(0.54)O(2) (or 0.5Li(2)MnO(3)-0.5LiCo(1/3)Ni(1/3)Mn(1/3)O(2)) by an electrochemical oxidation/reduction process in an electrochemical cell to study a reaction mechanism in detail before and after charging across a voltage plateau at 4.5 V vs Li/Li(+). Changes of the bulk and surface structures are examined by synchrotron X-ray diffraction (SXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (SIMS). SXRD data show that simultaneous oxygen and lithium removal at the voltage plateau upon initial charge causes the structural rearrangement, including a cation migration process from metal to lithium layers, which is also supported by XAS. This is consistent with the mechanism proposed in the literature related to the Li-excess manganese layered oxides. Oxygen removal associated with the initial charge on the high voltage plateau causes oxygen molecule generation in the electrochemical cells. The oxygen molecules in the cell are electrochemically reduced in the subsequent discharge below 3.0 V, leading to the extra capacity. Surface analysis confirms the formation of the oxygen containing species, such as lithium carbonate, which accumulates on the electrode surface. The oxygen containing species are electrochemically decomposed upon second charge above 4.0 V. The results suggest that, in addition to the conventional transition metal redox reactions, at least some of the reversible capacity for the Li-excess manganese layered oxides originates from the electrochemical redox reaction of the oxygen molecules at the electrode surface.

Geovibrio ferrireducens, a phylogenetically distinct dissimilatory Fe(III)-reducing bacterium

USGS Publications Warehouse

Caccavo, F.; Coates, J.D.; Rossello-Mora, R. A.; Ludwig, W.; Schleifer, K.H.; Lovley, D.R.; McInerney, M.J.

1996-01-01

A new, phylogenetically distinct, dissimilatory, Fe(III)-reducing bacterium was isolated from surface sediment of a hydrocarbon-contaminated ditch. The isolate, designated strain PAL-1, was an obligately anaerobic, non-fermentative, motile, gram-negative vibrio. PAL-1 grew in a defined medium with acetate as electron donor and ferric pyrophosphate, ferric oxyhydroxide, ferric citrate, Co(III)-EDTA, or elemental sulfur as sole electron acceptor. PAL-1 also used proline, hydrogen, lactate, propionate, succinate, fumarate, pyruvate, or yeast extract as electron donors for Fe(III) reduction. It is the first bacterium known to couple the oxidation of an amino acid to Fe(III) reduction. PAI-1 did not reduce oxygen, Mn(IV), U(VI), Cr(VI), nitrate, sulfate, sulfite, or thiosulfate with acetate as the electron donor. Cell suspensions of PAL-1 exhibited dithionite-reduced minus air-oxidized difference spectra that were characteristic of c-type cytochromes. Analysis of the 16S rRNA gene sequence of PAL-1 showed that the strain is not related to any of the described metal-reducing bacteria in the Proteobacteria and, together with Flexistipes sinusarabici, forms a separate line of descent within the Bacteria. Phenotypically and phylogenetically, strain PAI-1 differs from all other described bacteria, and represents the type strain of a new genus and species. Geovibrio ferrireducens.

Phase separation enhanced magneto-electric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films

PubMed Central

Alberca, A.; Munuera, C.; Azpeitia, J.; Kirby, B.; Nemes, N. M.; Perez-Muñoz, A. M.; Tornos, J.; Mompean, F. J.; Leon, C.; Santamaria, J.; Garcia-Hernandez, M.

2015-01-01

We study the origin of the magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films in experiments based on the converse magnetoelectric effect. The magnetization changes by around 30–40% upon applying electric fields on the order of 1 kV/cm to the BaTiO3 substrate, corresponding to magnetoelectric coupling constants on the order of α = (2–5)·10−7 s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields. We compare the magnetoelectric effect in pre-poled and unpoled BaTiO3 substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30 Å at the interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3. The magnetic granularity of the La0.7Ca0.3MnO3 film and the robust magnetoelastic coupling at the La0.7Ca0.3MnO3/BaTiO3 interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite. PMID:26648002

High performance Li2MnO3/rGO composite cathode for lithium ion batteries

NASA Astrophysics Data System (ADS)

Zhao, Wei; Xiong, Lilong; Xu, Youlong; Li, Houli; Ren, Zaihuang

2017-05-01

The novel composite Li2MnO3 (LMO)/reduced graphene oxide (rGO) has been synthesized successfully. Based on the scanning electron microscopy and transmission electron microscopy, LMO is found to distribute separately on the rGO sheets by forming a laminated structure, which is in favor of good electrical contact between the cathode active materials and the rGO matrix, and also facilitates the separation of LMO secondary particles with reduced size. Cyclic voltammetry and electrochemical impedance spectroscopy tests show that the charge transfer resistance decreases from 81.2 Ω for LMO to 29.6 Ω for LMO/rGO composite. The Li-ion diffusion coefficient of LMO/rGO composite is almost triple that of LMO. As a result, the LMO/rGO composite delivers an initial discharge capacity of 284.9 mAh g-1 with a capacity retention of 86.6% after 45 cycles at 0.1 C between 2.0 and 4.6 V. Cycle performance is even better at a higher current density 0.2 C while the retention ratio is up to 97.1% after 45 cycles. The rate capability is also significantly enhanced, and the LMO/rGO composite could exhibit a large discharge capacity of 123.7 mAh g-1 which is more than three times larger than that of LMO (40.8 mAh g-1) at a high rate of 8 C.

Sulfide-Induced Dissimilatory Nitrate Reduction to Ammonium Supports Anaerobic Ammonium Oxidation (Anammox) in an Open-Water Unit Process Wetland

PubMed Central

Jones, Zackary L.; Jasper, Justin T.; Sedlak, David L.

2017-01-01

ABSTRACT Open-water unit process wetlands host a benthic diatomaceous and bacterial assemblage capable of nitrate removal from treated municipal wastewater with unexpected contributions from anammox processes. In exploring mechanistic drivers of anammox, 16S rRNA gene sequencing profiles of the biomat revealed significant microbial community shifts along the flow path and with depth. Notably, there was an increasing abundance of sulfate reducers (Desulfococcus and other Deltaproteobacteria) and anammox microorganisms (Brocadiaceae) with depth. Pore water profiles demonstrated that nitrate and sulfate concentrations exhibited a commensurate decrease with biomat depth accompanied by the accumulation of ammonium. Quantitative PCR targeting the anammox hydrazine synthase gene, hzsA, revealed a 3-fold increase in abundance with biomat depth as well as a 2-fold increase in the sulfate reductase gene, dsrA. These microbial and geochemical trends were most pronounced in proximity to the influent region of the wetland where the biomat was thickest and influent nitrate concentrations were highest. While direct genetic queries for dissimilatory nitrate reduction to ammonium (DNRA) microorganisms proved unsuccessful, an increasing depth-dependent dominance of Gammaproteobacteria and diatoms that have previously been functionally linked to DNRA was observed. To further explore this potential, a series of microcosms containing field-derived biomat material confirmed the ability of the community to produce sulfide and reduce nitrate; however, significant ammonium production was observed only in the presence of hydrogen sulfide. Collectively, these results suggest that biogenic sulfide induces DNRA, which in turn can explain the requisite coproduction of ammonium and nitrite from nitrified effluent necessary to sustain the anammox community. IMPORTANCE This study aims to increase understanding of why and how anammox is occurring in an engineered wetland with limited exogenous

An evaluation of bacterial contamination of barriers used in periapical tissue regeneration: Part 2--Bacterial penetration.

PubMed

Sharma, Priya; Mickel, André K; Chogle, Sami; Sharma, Prem Nath; Han, Yiping W; Jones, Jefferson J

2008-03-01

To compare the relative penetration of Prevotella melaninogenica and Enterococcus faecalis through 3 guided tissue regeneration membranes: Atrisorb, Lambone, and OsseoQuest. It was hypothesized that OsseoQuest would show increased bacterial penetration when compared to Lambone and Atrisorb. Centrifuge tubes containing trypticase soy broth were sealed with circular sections of membranes and placed in test tubes containing culture media. The bacterial penetration was assessed by passage of bacteria from the outer tube culture media to the inner centrifuge tube media through the membrane. After incubation for 4 and 48 hours, the media from the outer and inner tubes were compared for bacterial count. P melaninogenica exhibited 91% penetration for Lambone in 2 days, while OsseoQuest displayed 87% penetration with E faecalis in the same time. Atrisorb displayed a minimal penetration with both bacteria (2%). Atrisorb displayed the least bacterial penetration, which may be attributed to membrane structure, chemical configuration, hydrophobicity, and porosity of tested membranes.

A Host-Produced Autoinducer-2 Mimic Activates Bacterial Quorum Sensing.