A Coherent Picture of the Hydrogen Oxidation and Evolution Reactions in Aqueous Solutions

Recent studies show the limitations of catalytic activity descriptor-based approaches to rationalize the kinetics of the hydrogen oxidation and evolution reactions (HOR/HER). Herein, we deposited several transition metals (TMs) onto Pt surfaces to disturb and probe the interface in alkaline solutions. The redox transition of these TMs in association with adsorption and desorption of reaction intermediates during the HOR/HER was monitored via in situ X-ray absorption spectroscopy. We propose that the TM facilitates the HOR by anchoring H₂O with the H-up configuration (↑H₂O_ad) that removes H_ad on Pt via the bifunctional mechanism, based on the first in situ experimental evidence for the presence of ↑H₂O_ad on surface Ru. Meanwhile, the TM promotes the HER of Pt by anchoring OH_ad to trigger the hard–soft acid–base (HSAB) mechanism for OH_ad removal. The revised 2B theory depicts a coherent picture of the HOR/HER kinetics in aqueous solutions.