Electrochemical Reconstruction Tailoring Catalyst Acidity for Boosted Alkaline Hydrogen Evolution

Electrochemical reconstruction is a powerful strategy to alter the chemical state and electronic structure of a catalyst surface for boosted electrocatalytic performance. Herein, we employ a classical MoNi4 binary alloy as an investigation platform for electrochemical reconstruction on the influence of hydrogen evolution reaction (HER) performance in alkaline electrolyte. The reconstructed MoNi4 catalyst exhibits remarkable alkaline HER activity, with ultralow overpotentials of 80 and 126 mV to deliver high current densities of 200 and 500 mA/cm2, respectively. Besides, the extremely low Tafel slope (30 mV/dec) directly suggests the fastest Tafel-type hydrogen generation kinetics on the MoNi4 alloy surface after electrochemical reconstruction. More importantly, there is no significant activity loss for the reconstructed catalyst electrode after continuous hydrogen production at a high current density of 500 mA/cm2 over 100 h, behaving as a potential catalyst for practical water electrolysis. Comprehensive morphology and spectroscopy characterizations demonstrate that these in situ generated oxyhydroxides (Mo-doped NiOOH, Mo-NiOOH), which cover the bulk alloy phase, possess strong Bro̷nsted-acid nature. These stable solid-acid sites display kinetically fast proton acceptance and donation behaviors in proton-insufficient electrolyte, thereby boosting the proton-coupled electron reaction in the alkaline HER process. Our work may provide a guideline to establish a direct relationship between the basic chemistry of the reconstructed oxide terminations and key proton activities in the alkaline HER process, and such insightful understanding will benefit the exploration of more low-cost but highly efficient catalysts toward water electrolysis and beyond.