Revelation of transport properties of ultra-thin ionomer films in catalyst layer of polymer electrolyte membrane fuel cells using molecular dynamics

Understanding the transport of oxygen, proton, and water in the catalyst layer is important for improving the performance of proton exchange membrane fuel cells. In this investigation, the nanostructure of ultrathin (3–7 nm) ionomer films and the influence of the film thickness on the transport properties are investigated using molecular dynamics simulations. The development of the water channel, corresponding to the transport of water and vehicular transport of proton, is accelerated with the increasing thickness of the ionomer films and the hydration level. However, the oxygen permeability, which is associated with the solubility and diffusivity of oxygen, is affected by the free volume and has a trade-off relationship with the properties of water. Notably, the hopping transport of protons is hindered by the increasing thickness of the ionomer films because of the nanostructure of the water phase, derived from the strong interaction with the Pt particles.