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Abstract: A novel fibrous MnO2 electrode for a fuel cell/battery system is fabricated on carbon fiber by the electrodeposition method. The characteristics of the fibrous MnO2 electrode are examined by electrochemical impedance spectra, galvanostatic performance and cyclic voltammetry. The experimental results indicate that the fibrous MnO2 electrodes are superior to pasted electrodes because of the following: (i) better contact between MnO2 and the electrical conducting material; (ii) high charge-transfer rate because of a smaller diameter than conventional electrodeposited MnO2 particles (thus it is expected that the specific surface area would be higher); and (iii) a low overpotential. The morphology and the crystal structure of the fibrous MnO2 electrode are investigated by scanning electron microscopy and X-ray diffraction, respectively. The entire surface of the carbon fiber is found to be coated with γ-MnO2 after 2h of electrodeposition at 0.01Adm−2 current density. [Copyright &y& Elsevier]

Abstract: Fuel cell/battery (FCB) systems are promising power generation/energy storage systems because of their bi-functionality as fuel cells and as secondary batteries. We investigated the required charging after the discharged manganese dioxide (MnOOH) by oxygen gas under the rest condition and during the fuel cell operation mode using manganese dioxide as a positive electrode for the FCB system. Electrochemical characterization was performed using cyclic voltammetry and galvanostatic measurements. Additionally, changes in the crystal structure and the chemical functional groups during the electrode reactions were monitored by X-ray diffractometry and Fourier transform infrared spectroscopy. The results indicated that MnOOH formed via the electrochemical discharge of manganese dioxide (MnO2) and that the oxyhydroxide can be chemically transformed back to MnO2 with gaseous oxygen (O2). The recharged MnO2 can be used as the cathode in a fuel cell with an O2 supply and it can also be electrochemically discharged without an O2 supply. In addition, we confirmed that MnO2 does not convert to Mn3O4 during the charge/discharge cycles if the redox reaction is maintained within a restricted range where a homogeneous process exists between MnO2 and MnOOH. The results in this study suggest that the FCB system can be constructed using MnO2 as the positive electrode and a metal hydride (MH) as the negative electrode, which can be rapidly charged to more than 70% of the theoretical capacity within 10min using pressurized H2 and electrochemically discharged, in an alkaline electrolyte. This system possesses a high-power generation efficiency, a high-energy density and a high load-following capability. [Copyright &y& Elsevier]

Electrochemical properties of composite films consisting of polyaniline/carboxydextran (PANI/carDEX) as a biofuel cell electrode platform were investigated. These composite films were formed on a planar gold surface through electropolymerization after a simple chemical modification of dextran with carboxyl groups. Cyclic voltammetry indicated that the composite films retained a redox activity in neutral pH environment. The PANI/carDEX composite films showed an electrocatalytic activity for the oxidation of ascorbic acid. The PANI/carDEX composite films also demonstrated an excellent electron-transfer mediating capability for the bioelectrocatalytic activation of glucose oxidase (GOx) toward the oxidation of glucose. [ABSTRACT FROM AUTHOR]