Molecular insights into ionic-liquid-regulated interfacial structure and transport in Pt/mesoporous-carbon for PEMFC cathodes

Abstract

Ionic-liquid filling provides a potential strategy for regulating local O2 and vehicular H3O+ transport in Pt-containing mesopores while modifying the molecular environment near Pt surfaces. All-atom molecular dynamics (MD) simulations were employed to compare seven imidazolium-based ionic liquids (ILs) in nanoscale Pt/mesoporous-carbon interfacial models by varying cation alkyl-chain length and fluorinated anion structure. Through-plane concentration profiles, radial distribution functions (RDFs), and mean-square-displacement (MSD) analyses were used to quantify hydration around Nafion sulfonate groups, O2 partitioning and mesopore-side O2 self-diffusion, vehicular H3O+ self-diffusion, and Pt–S spatial correlations. In the cation series, [C8mim][NTf2] lay at the upper end of both cation-series mobility ranges. In the anion series, [C2mim][C6F13SO3] gave the largest normalized integrated O2 occupancy index and mesopore-side O2 self-diffusion estimate, whereas [C2mim][NTf2] gave the largest vehicular H3O+ self-diffusion estimate. Pt–S RDFs revealed broad Pt-proximal sulfur distributions whose positions and shapes depended on IL structure.