Mitigation of mechanical membrane degradation in fuel cells – Part 1: Gas diffusion layers with low surface roughness

Abstract

Hygrothermal variations that arise during dynamic fuel cell operation are known to generate mechanical stresses in the ionomer membrane. Previous research has indicated that membrane electrode assembly (MEA) interaction effects may influence membrane degradation under such loads. The present objective is therefore to evaluate novel MEA design strategies for mitigating mechanical membrane degradation in fuel cells. In this case (Part 1), a gas diffusion layer (GDL) with low surface roughness is applied to suppress buckling-driven membrane failures. Laboratory-based X-ray computed tomography is used in a customized, time-resolved workflow for non-invasive four-dimensional characterization of membrane damage evolution during accelerated stress testing. Membrane crack development is the key failure mode preceded by fracture of the cathode catalyst layer. In comparison to high surface roughness GDL, the severity of membrane buckling is substantially reduced by adoption of the smoother GDL, contributing 2x greater lifetime. Accompanying finite element simulations of the unit fuel cell assembly show plastic strain accumulation in the buckled membrane and identified a critical range of GDL void sizes that influence membrane buckling. Overall, the improvement in GDL surface demonstrates substantial mitigation effect against fatigue-driven mechanical membrane degradation and failure, which is also corroborated by the numerical simulation results. • Novel MEA design strategies are shown to mitigate mechanical membrane degradation • CCM buckling into GDL voids is identified as the key mechanism for membrane failure • 2× higher RH cycling lifetime is achieved with low surface roughness GDLs • Complementary finite element simulations corroborate the experimental findings • A critical GDL pore radius is demonstrated for CCM buckling to occur