Heterojunction‐Associated Low‐Coordinated Copper Sites Enable pH‐Asymmetric Paired Electrolysis of 5‐Hydroxymethylfurfural

ABSTRACT Paired electrolysis of 5‐hydroxymethylfurfural (HMF) enables the concurrent production of 2,5‐furandicarboxylic acid (FDCA) and 2,5‐bishydroxymethylfuran (BHMF) as polymer precursors in an energy‐efficient manner. Its practical implementation is hindered by the scarcity of paired electrodes that can operate under disparate anodic/cathodic environments, as well as by limited process‐level understanding for pH‐asymmetric paired operation. Here, potential‐directed partial reconstruction of a common Cu 2 O nanowire scaffold generates anodic LC‐Cu 2 O/CuO and cathodic LC‐Cu/Cu 2 O electrodes. Atomic‐resolution microscopy and x‐ray absorption spectroscopy collectively reveal heterojunction‐containing mixed‐valence frameworks enriched in low‐coordinated Cu sites. Operando Raman spectroscopy, electrochemical measurements, and density functional theory calculations further reveal that on the anode, HMF adsorption is promoted and the regeneration of Cu III species is accelerated, while on the cathode, water dissociation is enhanced to produce reactive hydrogen, collectively facilitating the overall HMF conversion. Integrating LC‐Cu 2 O/CuO and LC‐Cu/Cu 2 O into a pH‐asymmetric cell verifies the superiority of a reinforced cation‐exchange membrane over a bipolar membrane in reducing the cross‐membrane potential drop, delivering a combined products Faradaic efficiency of 182.1%, an energy efficiency of 21.9%, and 100 h stability with suppressed products crossover. This work bridges electrode engineering and pH‐asymmetric device design, advancing paired electrolysis toward practical biomass electrorefining.