Ionomer migration within PEMFC catalyst layers induced by humidity changes

Abstract

The degradation of the membrane electrode assembly, originating from microstructural changes in the catalyst layer, inhibits the commercialization of polymer electrolyte membrane fuel cell. In particular, changes in relative humidity during starting/working conditions cause crack growth and propagation within the catalyst layer, but the reason is still not clear. Here, accelerated stress tests are designed from starting conditions (25 °C, 45% RH) to working conditions with different RHs (20%, 45% and 99%) at 85 °C for different cycles. For low working RH of 20%, no obvious change can be observed, while the accelerated stress test to high working RH induces apparent changes in the catalyst layer structure, with ionomer aggregation and migration leading to crack generation. The obtained results indicated that ionomer migration plays an important role in the structure changes of catalyst layer, suggesting that the design of ionomer with high stability and reliable water retention is necessary to improve the structural stability of the catalyst layer. Keywords: Catalyst layer degradation, Ionomer migration, Polymer electrolyte membrane fuel cell, Membrane electrode assembly