Unifying the Alkaline Hydrogen Evolution/oxidation Reactions Kinetics by Identifying the 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 (OHad)-water-alkali metal cation (AM+) adducts, on the basis of the observations that enriching the OHad 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 OHad-(H2O)x-AM+ in the double layer region facilitates the OHad removal into the bulk forming OH--(H2O)x-AM+ as per the hard-soft acid-base (HSAB) theory, thereby selectively promoting the HER. It can be detrimental to the HOR as per the bifunctional mechanism as the AM+ destabilizes the OHad, which is further supported by the CO oxidation results. This new notion may be important for alkaline electrochemistry.