Proton Flux Engineering via Built‐in Electric Fields in N‐doped CuO@Co ₃ O ₄ @Ni(OH) ₂ Heterostructure for Rechargeable Zn‐NO ₃ ⁻ /5‐Hydroxymethylfurfural Multielectron Transfer Systems

Abstract Electrocatalytic coupling of nitrate reduction (NO 3 RR) to ammonia with 5‐hydroxymethylfurfural (HMF) oxidation to 2,5‐furandicarboxylic acid (FDCA) enables simultaneous wastewater remediation and biomass valorization. However, developing efficient bifunctional electrocatalysts for these multiproton‐coupled electron transfer reactions remains challenging as conventional single‐active‐site catalysts inherently suffer from linear scaling relationships between intermediates and adsorption energies, particularly sluggish proton transfer. To address this, we engineered a triphasic N‐doped CuO@Co 3 O 4 @Ni(OH) 2 heterostructure with a gradient built‐in electric field (BIEF), which synergistically enhances interfacial charge polarization and accelerates proton transport through dynamic coupling effects in both reactions: sufficient *H supply for NO 3 RR and fast Ni(OH) 2 /NiOOH redox cycling during HMF oxidation (HMFOR), thus achieving unprecedented bifunctional performance: at − 0.4 V versus RHE, Faradaic efficiency (FE) for NH 3 reaches 96.49% with a yield rate of 45.36 mg h −1 cm −2 ; under 1.53 V versus RHE, the FDCA FE achieves 95.23% with a yield of 95.24%. The bifunctional design reduces energy consumption by 31.39% at 10 mA cm −2 in a NO 3 RR||HMFOR flow electrolyzer compared to traditional electrolytic water splitting. A rechargeable Zn‐NO 3 − /HMF battery shows 70–280 mV lower charging potential with exceptional cycling stability (>450 cycles). This work provides a new design paradigm for bifunctional electrocatalysts in sustainable energy conversion and waste valorization.