Identification of performance degradations in catalyst layer and gas diffusion layer in proton exchange membrane fuel cells

Degradations occur in both the catalyst layer (CL) and gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFC) due to different mechanisms. Identification of the locations and mechanisms of degradations is critical in mitigating them. In this study, performance degradation of a PEMFC is examined using an accelerated stress test (AST) protocol. Using a novel methodology of combining fresh and aged MEAs with either fresh or aged GDLs, the origins of losses in either CL or GDL are identified. Increase in mass transport resistance caused by increases in water saturation and in oxygen transport resistance are further isolated. The results show although kinetic degradation accounts for the primary performance decay, mass transport losses increase significantly due to the deterioration in water transport and increase in oxygen transport resistances. The increase in mass transport resistance in CL is greater than in GDL. The aged CL tends to retain more liquid water, causing significant decrease in actual porosity. Water transport in aged GDL also deteriorates and leads to increase in mass transport loss, especially under high relative humidity (RH). Oxygen transport resistance increases significantly in aged CL. However, there is no apparent increase in oxygen transport resistance in aged GDLs.