Abstract
Strongly alkaline electrolytes are typically used for electrochemical 5-hydroxymethylfurfural oxidation (HMFOR) to selective 2,5-furandicarboxylic acid (FDCA) production, despite HMF degradation. Although HMF remains stable in weakly alkaline media, slow kinetics due to limited OH(-) concentration hinder active FDCA formation. Herein, unlike the CuO or NiOOH catalyst, significantly improved direct aldehyde oxidation is demonstrated via the utilization of adsorbed OH ((*)OH) on the CuO/NiOOH interface surface, enabling complete conversion to FDCA even at mild pH. Operando measurements reveal that the CuO/NiOOH interface serves as a synergistic active site: Cu sites enhance (*)OH adsorption and utilization, while Ni sites promote HMF dehydrogenation through rapid Ni(OH)(2)/NiOOH redox cycling. The synergistic effect promotes highly selective FDCA production while preventing premature desorption of intermediates, which leads to outperforming activity compared with individual CuO and Ni(OH)(2). The interface-enriched CuO@NiOOH catalyst delivers >95% FDCA yield and Faradaic efficiency, and maintains long-term stability for 32.8 h under large-volume operation, owing to the enhanced HMF stability at pH 12. Water structure investigation further supports that the electrolyte microenvironment significantly affects HMFOR kinetics alongside the intrinsic activity of the interface. These insights provide a strategy for designing catalysts capable of efficient biomass-to-FDCA conversion across a broader pH range.