Microkinetic modeling of the oxygen reduction reaction at the Pt(111)/gas interface

A microkinetic model of the oxygen reduction reaction (ORR) on Pt(111) under a gaseous H2 and O2 atmosphere is used to predict and explain which compositions of H2 and O2 lead to the fastest rate of water formation for temperatures between 600 and 900 K. For a stoichiometric (2:1) mixture of H2 and O2 the rate-determing step is found to transition from O hydrogenation to O2 H dissociation over this same temperature range. These results are explained in terms of the temperature dependence of the surface coverages of O and H and are shown to be consistent with kinetic models aimed at understanding the ORR under electrochemical conditions.