Identifying the Transfer Kinetics of Adsorbed Hydroxyl as a Descriptor of Alkaline Hydrogen Evolution Reaction

Abstract

The key descriptor that dominates the kinetics of the alkaline hydrogen evolution reaction (HER) has not yet been unequivocally identified. Herein, we focus on the adsorbed hydroxyl (OH_ad ) transfer process (OH_ad + e^- ⇄ OH^- ) and reveal its crucial role in promoting the overall kinetics of alkaline HER based on Ni/Co-modified MoSe₂ model catalysts (Ni-MoSe₂ and Co-MoSe₂ ) that feature almost identical water dissociation and hydrogen adsorption energies, but evidently different activity trends in alkaline (Ni-MoSe₂ ≫ Co-MoSe₂ ) and acidic (Co-MoSe₂ ≥ Ni-MoSe₂ ) media. Experimental and theoretical calculation results demonstrate that tailoring MoSe₂ with Ni not only optimizes the hydroxyl adsorption, but also promotes the desorption of OH^- and the electron-involved conversion of OH_ad to OH^- , all of which synergistically accelerate the kinetics of OH_ad + e^- ⇄ OH^- and thereby the overall kinetics of the alkaline HER.