Mechanical degradation of catalyst layer under accelerated relative humidity cycling in a polymer electrolyte membrane fuel cell

Microstructure changes in the catalyst layer (CL) of polymer electrolyte membrane fuel cell (PEMFC) cause the performance degradation, especially under dynamic operating conditions. In this study, the effect of relative humidity (RH) cycling on the CL microstructure changes, the associated mechanisms, and fuel cell performance degradation are investigated. It is found that the Pt/C agglomerates size grows significantly due to RH cycling, especially at locations under the rib of bipolar plate. At 1000 mA cm(-2), the output voltage of the degraded CL drops about 6.56% in comparison with the fresh one. The electrochemical impedance spectrum and cyclic voltammetry are also measured correspondingly. Furthermore, a mathematical model is proposed to simulate the microstructure changes in the CL based on finite element method. Residual plastic strain may exist in the ionomer due to the swelling and shrinking behavior, resulting in the interfacial delamination between the ionomer and the Pt/C agglomerates. With the accumulation of plastic strain, the ionomer may be damaged during long term operation. The squeezed agglomerates may be combined each other during the swelling/shrinking process which can be seen as the agglomerates size growth mechanism.