Atomic-scale insights into the structure-activity relationship between water transport and water phase structure in proton exchange membranes with deposited Pt particles

Commercial development of proton exchange membrane fuel cells is hindered by membrane stability and durability. Platinum particles in the electrodes can deposit in the proton exchange membrane after long-term operation, reducing its performance. Here, Pt/Nafion membranes with different water contents and platinum particle sizes were built, and molecular dynamics simulations were conducted to assess the impact of deposited Pt nanoparticles on water transport capacity within the membrane and to capture nanoscale changes of water structure. The findings show that the Pt particles adsorb water molecules and form a partially coated water film on the surface, thereby reducing the water transport capacity, especially at low hydration levels. The absorbed water molecules exist in two forms, surface-adsorbed and indirectly-adsorbed water molecules. The former is the dominant factor determining the degree of inhibition of water diffusion in the membrane by Pt particles, whereas the latter appears in large numbers outside 3 nm particles, leading to a slightly weaker ability of 3 nm particles to inhibit water molecule diffusion compared to 2 nm particles. This study offers a basic comprehension of water transport properties in proton exchange membranes with platinum particles and guides the development of membranes with enhanced mass transfer capability.