Surface electron–hydronium ion-pair bound to silver and gold cathodes: A density functional theoretical study of photocatalytic hydrogen evolution reaction

Noble metal catalysts, such as silver and gold, play a significant role in photocatalytic water splitting to hydrogen for their high efficiency and environmentally-friendly nature. In this paper, a surface electron–hydronium ion-pair (EHIP) was proposed as an intermediate for photocatalytic hydrogen evolution reaction (HER) on silver and gold cathodes based on density functional theory (DFT) calculations. The EHIP is in the configuration of H3O+(H2O)ne−, where the hydronium H3O+ and the electron is separated by water layers. The electron bound in the EHIP can first be excited under light irradiation, subsequently inducing a structural relaxation into a hydrated hydrogen atom. Eventually, two hydrogen atoms recombine into a hydrogen molecule in the thin layer close to the electrode surface, e.g. at the outer Helmholtz plane (OHP). Additionally, Raman spectra of the interfacial EHIP species are calculated, which is in support of the presence of EHIP intermediates in the process of photocatalytic HER on silver and gold cathodes.

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