A Theoretical Consideration on the Surface Structure and Nanoparticle Size Effects of Pt in Hydrogen Electrocatalysis

Abstract

Microkinetic modeling and density functional theory (DFT) calculations are combined to understand the surface structure and nanoparticle size effects of Pt on the kinetics of hydrogen electrode reactions (HERs). The microkinetic modeling leads to a mechanism-free volcano relation between the exchange current density of HERs (j0) and the surface coverage of the reactive H adatoms at the equilibrium potential (θ0), making the activity trend of various catalytic surfaces for HERs predictable with θ0. It is shown that catalytic surfaces with θ0 values closer to 0.5 monolayer will have higher j0. A DFT calculation scheme is developed to determine the nature of the reactive H atoms and the corresponding θ0 values. The calculated results on Pt single crystal electrodes predict that j0 follows a trend that Pt(110) ≈ Pt(100) > Pt(111), whereas for Pt nanoparticles the j0 follows a trend that (100) facets > (111) facets ≈ edge rows, which in turn suggests a decrease of j0 with the decreasing particle size of Pt. It...