First-principles based analysis of the electrocatalytic activity of the unreconstructed Pt(100) surface for oxygen reduction reaction

We apply a rigorous computational procedure combining ab initio DFT calculations and statistical mechanics based methods to examine the electrocatalytic activity of the unreconstructed Pt(100) surface for oxygen reduction reaction. Using the cluster expansion formalism, we obtain stable interfacial water structures using Monte Carlo simulations carried out using parametrized interactions of water-water and water-metal. We find that both long-range and multibody interactions are important to describe the adsorbate interactions as a consequence of the mismatch between the preferred "hexagonal" water overlayer and the underlying square symmetry of the (100) surface. Our results indicate that the stable interfacial water structure is substantially different from that found on the Pt(111) surface. We compute the potential-dependent equilibrium coverages of oxygen-containing adsorbates, which shows that the surface is poisoned by strongly adsorbed OH. We construct the free-energy diagram of intermediates for oxygen reduction reaction on the Pt(100) surface and find that the limiting step is the reduction of the strongly adsorbed OH. We also find that, at a given potential, a higher degree of poisoning by OH is the reason unreconstructed (100) surfaces are catalytically less active than (111) surfaces. This study shows the importance of accurately capturing atomistic interactions beyond the nearest neighbor pairs.