Fatigue properties of catalyst coated membranes for fuel cells: Ex-situ measurements supported by numerical simulations

Abstract

The interactions between catalyst layers and membrane are known to have significant impact on the mechanical properties of the composite catalyst coated membrane (CCM) materials used in fuel cells. The mechanical fatigue durability of such composite CCM materials is investigated herein, and compared to the characteristics of pure membranes. Ex-situ uniaxial cyclic tension tests are conducted under controlled environmental conditions to measure the fatigue lifetime, defined by the number of stress cycles that the specimen can withstand before mechanical failure. The sensitivity of the CCM fatigue lifetime to the applied stress is determined to be higher than that of the pure membrane, and varies significantly with environmental conditions. The experimental results are then utilized to develop a finite element based CCM fatigue model featuring an elastic–plastic constitutive relation with strain hardening. Upon validation, the model is used to simulate the fatigue durability of the CCM under cyclic variations in temperature and relative humidity, which is critical for fuel cells but cannot be effectively measured ex-situ. When combined, the experimental and numerical methods demonstrated in this work provide a novel, convenient approach to determine the CCM fatigue durability under various hygrothermal loading conditions of relevance for fuel cell design and operation.