Physical Theory of Platinum Nanoparticle Dissolution in Polymer Electrolyte Fuel Cells

The loss or electrochemically active surface area (ECSA) causes severe performance degradation over relevant lifetimes of polymer electrolyte fuel cells. Using a simple physical model, we analyze the interrelations between kinetics of platinum nanoparticle dissolution, evolution of the particle size distribution, and ECSA loss with time. The model incorporates the initial particle radius distribution, and it accounts for kinetic processes involving Pt dissolution, Pt-O formation, and Pt-O dissolution. Employing reasonable simplifying assumptions to the governing equations, a full analytical solution was found under potentiostatic conditions. The simplified model predicts the evolution of the particle radius distribution as well as ECSA loss with time, in close agreement with experimental ex situ and in situ studies. The study indicates that the rates of chemical Pt-O dissolution, driven by the particle size dependence of the cohesive energy, may dominate over electrochemical dissolution. Fitting of the model to experimental data provides an effective surface tension and an effective rate constant of Pt-O dissolution. Implications of the model for the development of strategies to reduce ECSA loss are discussed.