Activating Co²⁺/Co³⁺ Redox Couple Mediated-Electrooxidation of 5-Hydroxymethyl Furfuryl Under Low Potentials

Cobalt-based electrocatalysts are promising candidates for electrochemical 5-hydroxymethylfurfural oxidation reaction (eHMFOR). However, the activity origin for eHMFOR on most cobalt-based electrocatalysts is the Co³⁺/Co⁴⁺ redox couple at the high-potential window, instead of the Co²⁺/Co³⁺ redox couple at the low-potential window, thus leading to a high onset potential above 1.3 V. Herein, we developed F-V_O-CoMoO₄ catalyst containing abound oxygen vacancies and lattice fluorine (F) heteroatom, which activates the Co²⁺/Co³⁺ redox couple for eHMFOR at the low-potential window, e.g., 1.15 V. Oxygen vacancies prompt the electrochemical generation of Co³⁺-OH_ads at low potentials, and meanwhile, lattice F heteroatoms enhance the electrophilicity of Co³⁺-OH_ads. Benefiting by those unique structure, F-V_O-CoMoO₄ catalyst effectively electro-synthesizes 2,5-furandicarboxylic acid from 5-hydroxymethylfurfural, with a high yield (95.3%) and Faradaic efficiency (96.1%). This work provides an intelligent strategy for achieving the low-potential eHMFOR mediated by the Co²⁺/Co³⁺ redox couple, unlocking significant potential for reducing the energy consumption in biomass conversion.