Insights into the oxygen transport through thin films on platinum surfaces: Effects of oxidation and dissolution

During the dynamic operation of proton exchange membrane fuel cells (PEMFCs), platinum nanoparticles (Pt NPs) experience surface structural evolution due to oxidation and dissolution processes. Understanding the oxygen transport through thin films on these structurally evolved Pt NPs is critical for enhancing Pt utilization efficiency. This work uses molecular dynamics (MD) simulations to examine how surface structural evolutions of Pt NPs affect oxygen transport resistances through ionomer or water films. We find that the edge and facet oxidation of Pt NPs alter the interactions between ionomer and Pt surfaces, and thus affect the local oxygen transport resistance (R_Pt^O₂).While for the Pt catalysts covered by water films, the Pt oxides favor the adsorption of water and thus leads to the increase of R_Pt^O₂. Additionally, the dissolution of edge and facet Pt atoms lead to stronger and weaker adsorption of ionomer, resulting in the decrease and increase of R_Pt^O₂, respectively. We ascribe the variation of R_Pt^O₂ to the evolutions of the dense layer formed on the Pt NPs, and propose a general relation to directly describe the dependence of R_Pt^O₂ on the structure of dense layer.