Unifying the Hydrogen Evolution and Oxidation Reactions Kinetics in Base by Identifying the Catalytic Roles of Hydroxyl-Water-Cation Adducts.

Despite the fundamental and practical significance of the hydrogen evolution and oxidation reactions (HER/HOR), their kinetics in base remain unclear. Herein, we show that the alkaline HER/HOR kinetics can be unified by the catalytic roles of the adsorbed hydroxyl (OH)-water-alkali metal cation (AM) adducts, on the basis of the observations that enriching the OH abundance via surface Ni benefits the HER/HOR; increasing the AM concentration only promotes the HER, while varying the identity of AM affects both HER/HOR. The presence of OH-(HO) -AM in the double-layer region facilitates the OH removal into the bulk, forming OH-(HO) -AM as per the hard-soft acid-base theory, thereby selectively promoting the HER. It can be detrimental to the HOR as per the bifunctional mechanism, as the AM destabilizes the OH, which is further supported by the CO oxidation results. This new notion may be important for alkaline electrochemistry.