Abstract: Nickel-cobalt-based hydroxides represent promising electrocatalysts for biomass valorization, replacing energy-intensive oxygen evolution reaction (OER) through low-potential oxidation of biomass to high-value chemicals. Understanding structural transformations during electrochemical oxidation is crucial for elucidating active species and engineering efficient catalysts. Herein, the electroactivation-induced transformation of Ce-regulated NiCo-LDHs (NCCe5-P) into CeO₂-modified NiCoOOH (NCCe5-R) was investigated. During this process, significant valence state evolution toward higher oxidation states occurs for Ni, Co, and Ce elements. CeO₂ modification coupled with electrochemical reconstruction induces abundant oxygen vacancy (V_O) formation in NCCe5-R. The V_O-rich NCCe5-R possesses more metal sites capable of oxidizing to high-valent states and accelerates the reaction kinetics between active species and 5-hydroxymethylfurfural (HMF). This rapid redox behavior stems from enhanced HMF adsorption capacity and accelerated charge transfer rates. Electrocatalytic evaluation demonstrates exceptional HMF oxidation reaction (HMFOR) performance: The optimized catalyst achieves complete HMF conversion (100%), high FDCA yield (99.5%), and outstanding Faradaic efficiency (99.1%). In HMFOR coupled with hydrogen evolution reaction systems, both NCCe5-P and NCCe5-R exhibit superior performance compared to overall water splitting systems, alongside robust stability and favorable comprehensive metrics.

Key words: Oxygen vacancies, Cerium oxide, Layered double hydroxides, Hydroxyl oxides, 5-hydroxymethylfurfural oxidation