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.

聚合物电解质膜燃料电池 (PEMFC) 催化剂层 (CL) 的微观结构变化会导致性能下降，尤其是在动态操作条件下。在这项研究中，研究了相对湿度 (RH) 循环对 CL 微观结构变化、相关机制和燃料电池性能退化的影响。发现由于 RH 循环，Pt/C 团聚体尺寸显着增加，特别是在双极板肋下的位置。在 1000 mA cm ^-2，与新鲜的 CL 相比，退化的 CL 的输出电压下降了约 6.56%。电化学阻抗谱和循环伏安法也相应测量。此外，提出了一种基于有限元方法的数学模型来模拟CL中的微观结构变化。由于溶胀和收缩行为，离聚物中可能存在残余塑性应变，导致离聚物和 Pt/C 附聚物之间的界面分层。随着塑性应变的积累，离聚物在长期运行过程中可能会损坏。在膨胀/收缩过程中，被挤压的团聚体可能相互结合，这可以看作是团聚体尺寸增长机制。