Stronger-than-Pt hydrogen adsorption in a Au₂₂ nanocluster for the hydrogen evolution reaction

Atomically precise metal nanoclusters have recently emerged as a novel class of catalysts for the hydrogen evolution reaction. From first-principles density functional theory, we show that the eight coordinatively unsaturated (cus) Au atoms in the Au₂₂(L⁸)₆ cluster [L⁸ = 1,8-bis(diphenylphosphino) octane] can adsorb H stronger than Pt, thereby being a potentially promising catalyst for the hydrogen evolution reaction (HER). We find that up to six H atoms can adsorb onto the Au₂₂(L⁸)₆ cluster and they have close-to-zero Gibbs free adsorption energies (ΔG_H). From the HOMO-LUMO gaps, frontier orbitals, and Bader charge analysis, we conclude that H behaves as a hydride or electron-withdrawing ligand in the Au₂₂(L⁸)₆ clusters, in contrast to the metallic H in thiolate-protected Au nanoclusters. Our study demonstrates that ligand-protected Au clusters with cus Au sites will be the most promising candidates for realizing Au-H nanoclusters and can act as excellent electrocatalysts for the HER.