Towards the understanding of the specifics of reactions in polymer-electrolyte fuel cells

In low-temperature hydrogen–oxygen polymer-electrolyte fuel cells, catalytic reactions usually occur on nm-sized Pt particles located on the walls of a porous carbon support. The electrolyte is usually a hydrated polymer (e.g., NAFION), which consists of hydrophobic chains and hydrophilic subchains and contain appreciable amount of water (up to about 40%). The heterogeneity of the electrolyte has the same length scale (about 10 nm) as the size of catalyst particles. To elucidate some specific aspects of reactions occurring under these conditions, we present Monte Carlo lattice simulations illustrating probable distributions of polymer and water near Pt particles. In the case of cathodic processes, the Pt surface is predicted to be free of polymer, the double layer near Pt to be uniform, and the role of polymer in the surface electrochemistry to be minor. During anodic processes, the polymer chains seem to directly participate in formation of the double layer near Pt, the field distribution in the double layer is far from uniform, and accordingly the role of polymer in surface electrochemistry is appreciable.