Kinetic Understanding of Metal Ions Doping in Enhancing the Electrocatalytic Ethanol Oxidation Performance of Nickel Hydroxides

Developing highly efficient electrocatalysts for organic electrosynthesis such as the nucleophile oxidation reaction (NOR) is of great significance for renewable energy utilization. However, the kinetic understanding of nickel-based catalysts in NOR still needs to be clarified. Herein, we synthesized several metal ions-doped Ni­(OH)2 and studied the mechanism of metal ions doping in enhancing the electrocatalytic NOR performance. Ethanol oxidation reaction (EOR) was used as a model reaction and a series of electrochemical measurements for the reaction order, electron transfer process, and metal redox kinetics of Ni­(II)/Ni­(III) were combined with the electronic structural characterization and theoretical calculation. The rate-determining step (RDS) of EOR was confirmed as the oxidation process of Ni­(II)–OH to Ni­(III)–O with one electron transfer; meanwhile, the kinetic mechanism of metal ions doping was unveiled: (1) decreasing the oxidation potential of Ni­(II)–OH to Ni­(III)–O was achieved by enhancing the interaction between the adjacent Ni and O and lowering the O–H bond dissociation energy barrier; (2) accelerating the cycling kinetics of Ni­(II)/Ni­(III) redox by bimetallic synergy improved the electronic transfer ability of materials. Our study is valuable in deeply understanding the kinetic mechanism of the synergetic electrochemical-chemically involved reaction processes in NOR.