Unraveling Adsorbed Hydroxyl-Mediated 5-Hydroxymethylfurfural Electro-Oxidation on a Cation-Defective Copper Oxide...

Copper oxide (CuO) is identified as a promising electrocatalyst for the oxidative upgrading of biomass derivatives, although the catalysis mechanism on CuO-based catalysts remains poorly understood. In this work, we report that cation defects in CuO enable a new electro-oxidation mechanism, designated as the adsorbed hydroxyl-mediated (AHM) pathway. A cation-defective CuO (CD-CuO) is prepared by the self-reconstruction of a vanadium-doped cuprous sulfide (V-Cu₂S) precatalyst, which exhibits high product yield and Faradaic efficiency exceeding 90% for the electro-oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). By combining operando Raman spectroscopy with density functional theory-based Raman spectrum simulations, we identify that hydroxyl species adsorbed on high-valence copper sites (Cu^2+δO-OH*) act as a redox mediator for HMF oxidation. The cation defects are found to lower the energy barrier for Cu^2+δO-OH* formation and enhance HMF adsorption, thereby promoting catalytic activity. Furthermore, the high performance of CD-CuO is well-maintained for more than 100 h in an anion exchange membrane electrolyzer. This work provides new insights into the catalytic mechanism and structure-performance relationships of copper-based catalysts.