The role of temperature in mechanical degradation of catalyst coated membrane in fuel cell: A 4D in-situ investigation based on X-ray computed tomography

Abstract

The application of polymer-electrolyte fuel cells for heavy-duty vehicles requires higher temperature and longer lifetime. However, the effect of temperature on the mechanical degradation mechanisms remains unclear, especially at higher temperature. In this study, the in-situ mechanical degradation behavior of catalyst coated membrane (CCM) is investigated at 70 °C, 80 °C and 90 °C using 4D X-ray computed tomography to track the evolution of mechanical damage throughout the lifetime, with the aim of clarifying the mechanical degradation mechanisms at different temperature to elucidate the role of temperature. Buckling in catalyst layer (CL) is observed at 70 °C, 80 °C and 90 °C, which is thought to be the key factor for mechanical degradation, and the degree of buckling at 90 °C is more severe. The path of buckling in CL is in alignment with cracks in microporous layer (MPL), occurring only in wider MPL crack regions. The deteriorated mechanical properties and increased plastic flow of CCM at higher temperature make CL more vulnerable to buckling, leading to the premature failure and reduced lifetime at 90 °C. In addition, the distribution of cracks at different temperatures is also different. While multiple cracks form due to buckling in the channel area at 90 °C, cracks are observed only at the edge of flow field plate at 70 °C and 80 °C without associated CL buckling progressing into cracks, which is ascribed to the competition between stress in channels and the loading conditions at edges. Finally, mechanisms of mechanical degradation at different temperatures as well as strategies for optimization of fuel cells are proposed.