Insights into how ionomer degradation affects oxygen transport resistance in catalyst layers

The side chain of ionomer is generally attacked by the free radicals during the long-term operation of proton exchange membrane fuel cells (PEMFCs). Investigating how ionomer degradation affects the oxygen permeation resistance through the thin film on the platinum (Pt) catalysts is crucial for enhancing PEMFC performance. In this work, we employed molecular dynamics (MD) simulations to explore the oxygen transport process to Pt surfaces under different ionomer degradation modes, and determine the local oxygen transport resistance ( [Formula: see text] ). Since the oxygen adsorption resistance (R_ads) is dominated, [Formula: see text] decreases after ionomer degradation due to the decrease of (R_ads) on Pt surfaces, although the oxygen diffusion resistance (R_dis) in the ionomer film increases. Different from the undegraded film, we find that the ratio of R_ads to [Formula: see text] decreases when the ionomer water content increases. Phase separations occurs when the chain-scission degree reaches 83.3 %. Besides, R_ads decreases while R_dif increases when the scission position is closer to the main chain. The above phenomena are ascribed to the microstructural evolutions of ionomer in the bulk region and that adsorbed on Pt surfaces.