Copper-Optimized Active Sites in Cobalt Oxide Nanocubesfor Selective Electrooxidation of 5‑Hydroxymethylfurfural

An effective design of a bimetallic cobalt-based spinel oxide catalyst to selectively convert 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA), replacing the oxygen evolution reaction (OER), demonstrates broad application prospects. However, the oxidation mechanisms differ markedly among various catalysts, and the structural transformations of transition metals within cobalt oxides remain insufficiently understood. Here we synthesized a Cu_0.29Co_2.71O₄ model catalyst using a facile solvothermal method. As the applied potential increased, Co(OH)₂ was generated on the surface of Cu_0.29Co_2.71O₄ and subsequently transformed into (Cu)CoO_<i>x</i>H_<i>y</i> via electrooxidation, followed by a rapid (nonelectrochemical) chemical oxidation reaction with HMF, achieving high selectivity (99.8%) and Faraday efficiency (91.6%) for the production of FDCA. Through comprehensive characterization coupled with electrochemical measurements and theoretical simulations, we found that the incorporation of copper effectively modulates the active sites of the cobalt oxide, which enhances OH^– adsorption and improves conductivity, thereby achieving superior HMF oxidation activity. This work provides valuable insights into designing highly active bimetallic spinel oxide electrocatalysts to accelerate the anode oxidation reaction, offering a promising alternative to the OER and promoting efficient biomass conversion.