Promotion and Stabilization of High-Valence CoO ₂ for the Efficient Electrooxidation of 5-Hydroxymethylfurfural (HMF) toward 2,5-Furandicarboxylic Acid (FDCA)

The electrochemical oxidation of HMF (HMFOR) to FDCA presents a promising alternative to the anodic oxygen evolution reaction (OER) in water electrolysis, offering reduced energy consumption and enhanced safety. However, achieving efficient FDCA production is hindered by the instability of HMF in alkaline media and the critical challenge of generating and stabilizing the high-valence metal active centers required for oxidizing the less reactive alcohol group in HMF at practical rates and potentials. This study addresses this challenge by constructing a Co(OH)2/Cu(OH)2 heterostructure on copper foam (CF) via a facile two-step synthesis. Comprehensive characterization, including in situ Raman spectroscopy, reveals significant electron transfer from Co to Cu within the heterostructure. This electronic interaction elevates the oxidation state of Co, thereby facilitating the generation of high-valence CoO2 and enhancing its stability compared to that of pure Co(OH)2. Consequently, the Co(OH)2/Cu(OH)2/CF electrode exhibits a high current density of 200 mA·cm–2 at 1.4 V vs RHE in 20 mmol/L (mM) HMF, along with nearly 100% carbon balance within 60 min. Mechanistic studies confirm that the stabilized CoO2 centers promote strong adsorption of HMF, particularly activating the alcohol group for efficient oxidation to FDCA. This work provides a viable electronic structure modulation strategy for stabilizing high-valent metal centers through interfacial electronic modulation toward efficient biomass electrooxidation.