Kinetic Multi-reaction Model of Platinum Nanoparticle Oxidation and Cathodic Dissolution in a Wide Potential Window

Mathematical modeling provides a powerful framework for understanding and mitigating degradation in catalyst materials such as platinum nanoparticles. A hallmark of platinum degradation during voltage cycling is the appearance of two distinct maxima in the dissolved Pt concentration: a smaller peak upon increasing potential and a larger peak upon decreasing potential. To explain this observation, we propose a kinetic multi-reaction model of Pt nanoparticle oxidation and dissolution, which describes dissolution as an interplay between direct electrochemical dissolution, passivation of the Pt surface, and the electrochemical dissolution of Pt oxides. The model is calibrated using cyclic voltammograms and time traces of Pt ion concentrations measured for two Pt catalyst samples with different nanoparticle sizes and different supports (carbon-supported 3 nm and unsupported 30 nm particles). The model results show very good agreement with the experimental data and indicate that the dissolution dynamics are indeed governed by oxide surface passivation and dissolution. Furthermore, comparison of results for different catalysts shows that the observed differences in Pt dissolution arise not only from variations in reaction rates on particles of different sizes but also from differences in the catalysts’ microscopic structure, which significantly influence Pt loss through diffusion.