Unveiling Cation-Dependent Electrocatalytic Behavior in HMF Oxidation over Organic-Ligand-Tailored Charged Cu-Ni(OH)2

Electrocatalytic 5-hydroxymethylfurfural oxidation (HMFOR) is a sustainable route for biomass valorization to 2,5-furandicarboxylic acid (FDCA), yet balancing the competitive adsorption of HMF and OH− at the electrode−electrolyte interface is pivotal for boosting catalytic activity and selectivity. Herein, we report a terephthalic acid (PTA) modification strategy to tailor Cu-Ni(OH)2 with tunable metal valence and controllable surface charge, fabricating positively charged Cu-Ni(OH)2 and negatively charged Cu-Ni(OH)2-PTA. PTA functionalization elevates the Ni oxidation state and reinforces HMF adsorption on the catalyst surface. In situ surface-enhanced Raman spectroscopy and electrochemical impedance spectroscopy confirm that the negatively charged surface of Cu-Ni(OH)2-PTA efficiently mitigates the steric hindrance of hydrated ions and preserves a fully hydrated Cs+ interfacial microenvironment. This synergy optimizes the adsorption equilibrium of HMF and OH− via efficient and persistent HMF capture, enabling continuous enhancement of HMFOR activity. Consequently, Cu-Ni(OH)2-PTA delivers superior HMFOR performance in CsOH electrolyte, including a high FDCA Faradaic efficiency (98.2%), large current density, excellent cycling stability over 10 cycles, and stable operation for 120 h in a membrane electrode assembly (MEA) system. Notably, a high FDCA Faradaic efficiency of ∼86% is retained even in a pH 13 electrolyte with 1 M Cs+. This work elucidates the coupled effects of metal valence, surface charge, cation hydration, and interfacial water structure on HMFOR, providing a universal interfacial engineering principle for designing advanced electrocatalysts for efficient biomass electrooxidation.