Non-electrochemical degradation: a critical hidden factor limiting durability of ultra-low platinum PEMFCs

Abstract

Reducing the dosage of precious metal catalysts is the most direct way to lower the cost of PEMFCs. Numerous studies have addressed the significant performance degradation observed at high current densities due to low Pt loading. However, few investigations have systematically and comprehensively examined the stability of ultra-low Pt PEMFCs. In this work, both electrochemical and non-electrochemical degradation mechanisms of ultra-low Pt PEMFCs are explored experimentally, and the underlying degradation mechanisms are elucidated through simulation. The experimental results indicate that, in ultra-low Pt PEMFCs, non-electrochemical cycling causes substantially greater output power degradation than electrochemical aging. Specifically, the maximum power density decreases by 40.7 % after 200 relative humidity cycles, whereas it remains stable after 10,000 catalyst aging AST (accelerated stress test). The primary cause of output power degradation is the detachment of ionomers from the surface of the carbon-supported catalyst (Pt/C) during non-electrochemical cycling, which leads to an inhomogeneous ionomer distribution. Simulation results reveal that stresses generated by ionomer expansion due to water absorption and contraction caused by water desorption induce the detachment of ionomers from the Pt/C surface. This study offers guidance for developing PEMFCs with reduced platinum content and enhanced durability.