Switching Urea Oxidation Reaction Pathways by Regulating Multi-Component Sites on Chlorine-Doped Nickel-Cobalt...

Urea oxidation reaction (UOR) has been considered as a promising alternative to the oxygen evolution reaction for hydrogen production. So far, there are two proposed catalytic reaction alternatives for UOR, including a conventional direct six-electron process and a rarely reported two-stage reaction pathway. Herein, we successfully achieved the switching of UOR pathways by artificially increasing/decreasing the concentration of oxygen vacancies monotonously on nickel-cobalt hydroxides. The "multi-component active sites" and the UOR structural-pathway relation were clearly elucidated by extensive experimental characterizations and density functional theory (DFT) calculations. With rich "multi-component active sites", chlorine-substituted nickel-cobalt hydroxides (NiCoClOH) exhibit a record performance for Ni³⁺-active sites (1.22/1.34 V versus reversible hydrogen electrode to achieve 10/100 mA cm^-2 in 1 M KOH with 0.33  M urea). This work not only reported highly efficient electrocatalysts for UOR, but also paved new insights for the structure-pathway relationship during UOR.