Unlocking the role of oxygen vacancies in FeO/NiO/Ni for boosting 5-hydroxymethylfurfural electrooxidation

Electrocatalytic oxidation of 5-hydroxymethylfurfural (HMFOR) offers an energy-efficient route to high value-added chemicals. There is an urgent demand for high-performance non-precious metal catalysts. Herein, the oxygen-deficient FeO/NiO/Ni was synthesized, which has high performance for HMFOR with a conversion rate of 100%, a selectivity of 98.6% for 2,5-furandicarboxylic acid (FDCA), and a Faradaic efficiency of 94.1% at 1.5 V (vs. RHE), superior to most reported non-precious metal catalysts. The efficient catalytic activity of FeO/NiO/Ni is attributed to the high specific surface area and enhanced adsorption and activation of HMF by oxygen vacancies, thereby reducing the rate-limiting step energy barrier of 5-hydroxymethyl-2-furancarboxylic acid to 5-formyl-furancarboxylic acid (*HMFCA→*FFCA). Ni 3+ acts as the active site for direct HMF oxidation catalysis, while Fe doping induces oxygen vacancies that facilitate the formation and stabilization of Ni 3+ species, enhancing their formation and catalytic functionality.