Complex capacitance analysis of ionic resistance and interfacial capacitance within cathode layers of PEMFC and DMFC electrodes

For PEMFC and DMFC catalyst layers, a complex capacitance analysis of impedance data was developed to evaluate the catalyst/ionomer interfacial capacitance and ionic resistance of ionomer networks, without non-linear data fitting. Assuming no Faradaic reactions, equivalent circuits for the catalyst layers were suggested, and it was confirmed that the plots of the real and imaginary parts as a function of ac frequency are determined by the catalyst/ionomer interfacial capacitances and RC time constants, which are important characteristics for high fuel cell performances. By performing a complex capacitance analysis, the interfacial capacitances and ionic resistances of PEMFC MEAs can be experimentally obtained at various relative humidities, proving that the catalytic activity in fuel cell operation depends on ionic resistances as well as on the catalyst/ionomer interfacial area. In addition, the effects of various MEA preparation methods on the ionomer distributions and DMFC performances were analyzed by a complex capacitance analysis.