Vacancy-induced catalytic mechanism for alcohol electrooxidation on nickel-based electrocatalyst

Owing to outstanding performances, nickel-based electrocatalysts are commonly used in electrochemical alcohol oxidation reactions (AORs), and the active phase is usually vacancy-rich nickel oxide/hydroxide (NiOxHy) species. However, researchers are not aware of the catalytic role of atom vacancy in AORs. Here, we study vacancy-induced catalytic mechanisms for AORs on NiOxHy species. As to AORs on oxygen-vacancy-poor beta-Ni(OH)2, the only redox mediator is electrooxidation-induced electrophilic lattice oxygen species, which can only catalyze the dehydrogenation process (e.g., the electrooxidation of primary alcohol to carboxylic acid) instead of the C-C bond cleavage. Hence, vicinal diol electrooxidation reaction involving the C-C bond cleavage is not feasible with oxygen-vacancy-poor beta-Ni(OH)2. Only through oxygen vacancy-induced adsorbed oxygen-mediated mechanism, can oxygen-vacancy-rich NiOxHy species catalyze the electrooxidation of vicinal diol to carboxylic acid and formic acid accompanied with the C-C bond cleavage. Crucially, we examine how vacancies and vacancy-induced catalytic mechanisms work during AORs on NiOxHy species. Oxygen vacancy-induced adsorbed oxygen-mediated mechanism (VO-AOM) is essential to the electrooxidation of R-CHOH-CH2OH to R-COOH and HCOOH (VDOR) over nickel-based catalysts, especially for the C-C bond cleavage process.+image