Electrochemical impedance spectroscopy investigation on the ionomer degradation modeling of the anode using a porous microelectrode

In this study, the modeled degradation behavior of ionomer at the anode was investigated by combining the electrochemical impedance spectroscopy (EIS) and porous microelectrode techniques. We prepared the PME packed with the powder mixtures of Pt/C and Nafion with different ratios of Pt/C:Nafion = 1:1, 1:0.6, and 1:0 for modeling non-degraded, partly degraded and completely degraded ionomer. Based on the EIS results, both the charge transfer and mass transfer resistances increased with the decrease of Nafion content. The increased charge transfer resistance suggests a suppression of the hydrogen oxidation reaction rate at the electrode with degraded ionomer due to the decrease in the electrochemical surface area of Pt. On the other hand, the increase of mass transfer resistance is attributed to the decrease of Nafion content, which suppressed the ionic conductivity and blocked the reactant pathway. Moreover, a significantly higher adsorption resistance of the electrode with completely degraded ionomer was observed, indicating the adsorption site of the intermediates, i.e., the electrochemical surface area of Pt on the electrode without Nafion is lower than that of the electrode packed with the powder mixture of Pt/C and Nafion.