Ab initio study of oxygen reduction mechanism at Pt(4) cluster.

We used density functional theory to investigate the reaction pathway of oxygen reduction/water splitting at a tetrahedral Pt(4) cluster. Four extra water molecules were included to account for the effect of water in mediating elementary surface processes. We propose a 6-step reaction sequence that includes a proton transfer between neighbouring active sites. Thermochemical considerations and the nudged elastic band method were employed to calculate reaction and activation energies for the elementary reaction steps. We generated the free energy diagram along the reaction path for various applied potentials. This plot provides vital information on the stability of intermediates and the rate determining processes in oxygen reduction and water splitting. Results suggest that removal of the reaction product, viz. molecular oxygen or water, is an energetically strongly hindered step in either direction.