Electrochemical Behaviors of Mixed Conducting Oxide Anodes for Solid Oxide Fuel Cell

To clarify guidelines for a high-performance mixed conducting oxide anode, electrochemical behaviors of mixed conducting oxide anodes were studied on the oxides, , , , , , , and . The hydrogen oxidation on the oxide anodes is studied by ac impedance and steady-state polarization measurements. In the ac impedance measurements, a slow relaxation process of the order of was observed with the -based and anodes. The corresponding pseudocapacitances are . These pseudocapacitances are identified as the chemical capacitance due to the variation of the nonstoichiometric oxygen content of the electrode material. At the same electrode potential, the -based anodes showed a far higher steady-state current than the - and the -based anodes. The extension of the reaction zone beyond the three phase boundary is estimated from our experimental results. The reaction zone of the anode extends from the three-phase boundary to the electrode/gas interface. To estimate what determines the electrode performance of the oxide anodes, the effect of the material property and the electrode microstructure was studied. The effect of the material property is much larger than that of the electrode microstructure. High ionic conductivity and catalytic activity with a certain level of electronic conductivity is required for a high-performance oxide anode.