Anchoring hydroxyl intermediate on NiCo(OOH)(x) nanosheets to enable highly efficient electrooxidation of benzyl alcohols

Selective oxidation of alcohols to the carboxylic acid plays an important role in the production of valuable chemicals. Herein, NiCo hydroxide (NiCo(OOH)(x)) nanosheets with a thickness of similar to 4 nm were controllably fabricated in a facile way efficient for the electrooxidation of benzyl alcohol (BAL) to benzoic acid (BAD). Mechanistic studies confirmed the hydroxyl active intermediate (-OH*) generated on the surface of NiCo(OOH)(x) nanosheets through operando electrochemical impedance spectroscopy and the electron paramagnetic resonance spectroscopy analysis during the electrooxidation process. Importantly, we discovered that the -OH* was crucial to boost the selective oxidation of BAL by attacking the hydroxyl end group to achieve carboxylic acid. The early onset potential of 1.16 V-RHE in the presence of BAL was below 1.23 V-RHE for oxygen evolution reaction. The rotating ring-disk electrode further revealed that the electrocatalytic BAL oxidation reaction occurred earlier in the oxygen evolution reaction. In 150 mM BAL, NiCo(OOH)(x) nanosheets generated a high BAD selectivity of > 99% and full conversion of BAL in 3 h. The experimental and theoretical calculation revealed that the dominant pathway of BAL oxidation was the interaction between nucleophilic BAL with -OH* to form BAL-OH* directly by dehydrogenates, thereby producing BAD with high efficiency. This research sheds mechanism insights on the electrocatalytic alcohols oxidation reaction.