Hydrogen Bridge‐Mediated Efficient Electrooxidation of 5‐Hydroxymethylfurfural on Ni(OH)₂─PO₄³⁻/Ni₃(PO₄)₂ Heterojunctions

Accelerating proton deintercalation and transfer on the catalyst surface is crucial for the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) into the high-value 2,5-furanodicarboxylic acid (FDCA). Herein, we have constructed a Ni(OH)₂─PO₄ ^3-/Ni₃(PO₄)₂ heterojunction catalyst that demonstrates exceptional selectivity (97.16%), yield (94.16%), and Faraday efficiency (94.31%) in the selective oxidation of HMF toward FDCA. The incorporation of PO₄ ^3- groups triggers the formation of hydrogen bridges and reconfigures the interfacial charge distribution, facilitating the activation and subsequent proton deintercalation of lattice-hydroxyl-groups to generate active Ni³⁺─O catalytic sites (PO₄ ^3-⋯H─O─Ni²⁺ → HPO₄ ^2- + Ni³⁺─O). Both density functional theory calculations and pH-dependent experiments emphasize the crucial function of these hydrogen bridges as proton ferries, effectively boosting the proton transfer efficiency during HMF oxidation. Theoretical studies unveil that the rate-controlling step for OH adsorption on Ni(OH)₂─PO₄ ^3- occurs via the hydrogen bridge connecting the PO₄ ^3- group with the α-C atom in *HMF-H intermediate (PO₄ ^3-⋯H─O⋯COR → PO₄ ^2-─H⋯O─COR), significantly reducing the energy barrier for HMF oxidation. This study introduces a novel hydrogen bridge-mediated electrooxidation mechanism that holds great potential for advancing biomass conversion technologies.