Optimization of competitive adsorption via oxygen vacancies on NiCo hydroxides for selective electrosynthesis of adipic acid coupled with hydrogen production

Abstract

The electrosynthesis of adipic acid through the cyclohexanol oxidation reaction (COR) can address the pollution issues associated with the traditional process. However, the complexity of the electrooxidation process and unclear dehydrogenation and oxidation mechanisms limit its application. Herein, we report oxygen vacancy (V_O) modification on NiCo hydroxides for the selective electrosynthesis of adipic acid. In situ IR and DFT calculations revealed significantly enhanced adsorption capacity and an optimized process for the co-adsorption of OH⁻ and organic compounds. The V_O promotes the conversion of ketone intermediates into glycol with the addition of H₂O while inhibiting the formation of ketone alcohols. In situ synchrotron radiation and Raman analyses reveal the reversible remodeling processes of Ni²⁺–OH and Ni³⁺–OOH during the COR. Consequently, V_O-NiCo demonstrated excellent COR performance (1.32 V vs. RHE onset potential) with conversion, adipic acid selectivity, and faradaic efficiency values of 98.4%, 95.6%, and 95.2%, respectively. The system generates 8.2 times more hydrogen compared with pure water splitting at the cathode. This integrated electrocatalytic system shows potential for large-scale production of H₂ and adipic acid, offering new insights for designing advanced electrocatalysts for cost-effective and sustainable energy conversion.