Particle Proximity Effect in Nanoparticle Electrocatalysis: Surface Charging and Electrostatic Interactions

Understanding the structure activity relation of nanostructured electrocatalysts is crucial for advances in emerging electrochemical energy systems, most prominently polymer electrolyte fuel cells and electrolyzers. In this realm, the surface-specific activity of platinum is a peculiar function of particle size and interparticle spacing. Previous attempts to rationalize the particle size and proximity effects focused on geometric and electronic factors and they largely ignored the role of the support. The present study focuses on a consistent treatment of electrostatic reaction conditions around Pt nanoparticles, taking into consideration the specific surface charging properties of Pt and the support material. The model reveals a double-layer overlap regime in which the surface-specific activity is significantly enhanced by decreasing the interparticle spacing. Relevance of the model in explaining the particle proximity effect is demonstrated.