Construction of CoO–Cu₂O Composites with Enhanced HMF Adsorption and Passivated Water Oxidation for High-Efficiency Biomass Valorization

Electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) to high-value-added products shows great promise for sustainable chemical production and reduced fossil resource utilization, yet exploring highly efficient HMFOR electrocatalysts with high current densities and Faraday efficiency (FE) remains a great challenge. Co-based catalysts could enable 5-hydroxymethylfurfural (HMF) oxidation at low potentials, but the slow kinetics as well as competing oxygen evolution reaction (OER) often results in low FE, especially under high current densities. Meanwhile, Cu-based catalysts with poor OER activities could achieve high FE for HMFOR but at the cost of low current densities. Herein, bimetallic Co-Cu oxide composites (CoO-Cu2O) are constructed to combine the advantages of both, while the synergistic effect between CoO and Cu2O could modulate oxygen vacancy (VO) defects, boost electron transfer from Cu to Co species, which improves HMF adsorption and accelerate HMF conversion. Besides, the competitive OER is suppressed by Cu-based species with an apparent inhibitory effect. As a result, the optimized CoO–Cu2O composites achieve a remarkable current density of 355.7 mA cm–2 at 1.425 V vs RHE for HMFOR. Besides, nearly 100% of HMF conversion and a high FEFDCA of 99.6% are obtained. This work highlights the advantage of constructing transition bimetallic catalysts in synergistically improving HMFOR performance and provides new insights into the design of efficient catalysts.