Micro-kinetic mean-field model of subsurface oxidation in a platinum electrocatalyst

The ability to predict surface reactions on heterogeneous nanoparticle catalysts is important for the design and development of high-performance materials and for controlling the reaction conditions. Herein, we formulate a mean-field model of interacting reaction intermediates involving subsurface species. The model uses a partition function based on a statistical lattice gas model to describe the surface phase, with thermodynamic relationships satisfied using the derived intermediates. Kinetic rate equations were systematically formulated, aided by linear relationships between activation barriers and reaction free energies. The model was applied to oxide growth on a Pt electrocatalyst for use in proton-exchange membrane fuel cells, which demonstrated that the model reasonably reproduces the experimentally measured amounts of oxide formed over a wide time range. Kinetic simulations and density functional theory calculations consistently indicate the significance of the self-stabilizing interactions of subsurface oxides in accurately simulating Pt-oxide formation and reduction.