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Unifying the Alkaline Hydrogen Evolution/oxidation Reactions Kinetics by Identifying the Roles of Hydroxyl-Water-Cation Adducts
preprintsubmitted on 26.09.2018, 18:06 and posted on 27.09.2018, 14:35 by Ershuai Liu, Jingkun Li, Li Jiao, Huong Thi Thanh Doan, Zeyan Liu, Zipeng Zhao, Yu Huang, Kuzhikalail. M. Abraham, Sanjeev Mukerjee, Qingying Jia
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.