Theoretical investigations of surface oxides on platinum and platinum alloy catalysts for fuel cell applications

摘要

The interaction of oxygen with metal surfaces can lead to various structures;udthese include surface oxide films, oxygen penetration in the subsurfaceudregion and bulk oxides, at certain partial pressures and temperatures.udThis research focuses on the oxygen reduction reaction (ORR)udwithin the proton exchange membrane fuel cell (PEMFC).udPEMFC are believed to be kinetically limited for the ORR due to a lossudof surface area at the cathode as a result of oxidation. One explanationudfor this phenomenon is the “so called place exchange mechanism” whichudleads to a thin surface oxide being formed. In an attempt to understand andudverify this hypothesis, Pt and Pt/Ni alloys have been modelled in order touddetermine the relative propensity of surface oxide film formation.udDensity functional theory (DFT) has been used to model various facets ofudthe catalyst particles, in particular the (111) and (100) surfaces. In addition,uda range of oxygen coverages at high symmetry sites and oxide thin filmsudhave also been modelled as intermediates in the place exchange mechanism.udThe DFT data obtained from these calculations have been used in audstatistical thermodynamics model. This allows one to bridge the temperatureudand pressure gap between the technological relevant conditions of theudPEMFC and the electronic structure calculations.