Theoretical and Experimental Understanding of Hydrogen Evolution Reaction Kinetics in Alkaline Electrolytes with Pt-Based Core-Shell Nanocrystals.

The free energy of H adsorption (ΔGH) on a metallic catalyst has been taken as a descriptor to predict the hydrogen evolution reaction (HER) kinetics but has not been well applied in alkaline media. To assess this, we prepare Pd@Pt and PdH@Pt core-shell octahedra enclosed by Pt(111) facets as model catalysts for controlling the ΔGH affected by the ligand, the strain, and their ensemble effects. The Pt shell thickness is adjusted from 1 to 5 atomic layers by varying the amount of Pt precursor added during synthesis. In an alkaline electrolyte, the HER activity of core-shell models is improved either by the construction of core-shell structures or by the increased number of Pt shells. These experimental results are in good agreement with the ΔGH values calculated by the first-principles density functional theory with a complex surface strained core-shell slab model. However, enhanced HER activities of Pd@Pt and PdH@Pt core-shell nanocrystals over the Pt catalyst are inconsistent with the thermodynamic ΔGH scaling relationship only but can be explained by the work function and apparent ΔGH models that predict the interfacial electric field for the HER.