Electrocatalysts and membrane for direct ethanol-oxygen fuel cell with alkaline electrolyte

Abstract

Results of studies of anodic (RuNi/C) and cathodic (PtCo/C; CoN4/C) catalysts, polybenzimidazole membrane, and membrane-electrode assemblies on their basis for alkaline ethanol-oxygen fuel cell are presented. It is shown that the anodic catalyst RuNi/C optimized in its composition (Ru: Ni = 68: 32 in atomic percent) and the metal mass on carbonaceous support (15–20%) is sufficiently effective with respect to ethanol oxidation; it is well superior to commercial Pt/C- and RuPt/C-catalysts when calculated per unit mass of the precious metal. The effect of electrolyte composition, electrode potential, and temperature on the CO2 yield is studied by chromatographic analysis of the ethanol oxidation products. It is shown that the highest CO2 yield (the process involves the C-C bond break) is achieved at low electrolysis overvoltage and elevated temperature. The mean number of electrons given up by C2H5OH molecule approaches 10 at temperatures over 60°C. The studied cathodic catalysts form the following series of their specific activity in the oxygen reduction reaction: (20 wt % Pt) E-TEK ≥ (7.3 wt % Pt) PtCo/C > CoN4/C; however, in the presence of alcohol the activity series is reversed. On this reason fuel cell cathodes were prepared by using synthesized CoN4/C-catalyst. For the alkali-doped polybenzimidazole membrane the conductivity and ethanol crossover were determined. A membrane-electrode assembly for platinum-free alkaline ethanol-oxygen fuel cell is designed. It comprised anodic (RuNi/C) and cathodic (CoN4/C) catalysts and polybenzimidazole membrane. The period of service of the fuel cell exceeded 100 h at a voltage of 0.5 V and current of 100 mA/cm2.