Lewis Acid–Base Interactions in Ru-Stabilized NiFe (Oxy)Hydroxide Promoting Biomass Upgrading at Industrial Currents

Achieving the continuous conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) at industrial current densities holds great promise for plastic manufacturing but poses significant challenges in maintaining long-term stability. Herein, we introduce single-atom Ru sites exhibiting Lewis acidic properties stabilized on nickel–iron-layered double hydroxide (Ru@NiFe) through defect-mediated anchoring and strong covalent metal–support interactions, specifically designed for efficient biomass upgrading. In a practical electrolyzer, Ru@NiFe achieves a robust FDCA conversion rate of 159.3 mg cm–2 h–1 with 90% Faradaic efficiency, maintaining stable operation for over 500 h at an industrial density close to 270 mA cm–2 without significant activity loss. Operando spectroscopies and theoretical investigations reveal that electrophilic single-atom Ru sites establish strong Lewis acid–base interactions, promoting the formation of active Ni3+δ (0 < δ < 1) species and enhancing adsorption toward HMF. This promotion enables an enhanced dynamic oscillation between Ni2+ and Ni3+δ during the electrooxidation–reduction of HMF, effectively preventing overoxidation of Ni3+δ by preferentially capturing released protons, thus ensuring long-term operation.