<p>Electrocatalytic conversion of biomass-derived compounds and nitrate pollutants offers a promising route toward sustainable chemical synthesis and environmental remediation. In this work, a bifunctional NiO-NiCoP catalyst with a well-defined heterogeneous interface is synthesized via a low-temperature co-precipitation, annealing and phosphidation process to enable the coupled electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) and nitrate reduction reaction (NO₃⁻RR). X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), open-circuit potential (OCP), and <i>in-situ</i> electrochemical impedance spectroscopy (<i>in-situ</i> EIS) confirm the formation of the heterogeneous interface, which facilitates electron redistribution, enhances charge transfer, and optimizes reactant adsorption. The catalyst exhibits excellent HMFOR activity, achieving 99.46% HMF conversion, 97.23% 2,5-furandicarboxylic acid (FDCA) yield, and 97.62% Faradaic efficiency (FE) at 1.40 V vs. RHE. For NO₃⁻RR, nearly 100% FE and an NH₃ yield of 8.82 mg h⁻¹ cm⁻² are obtained at −0.40 V vs. RHE. In a paired HMFOR//NO₃⁻RR electrolyzer, the NiO-NiCoP catalyst demonstrates superior current density, product selectivity, and long-term stability compared to conventional oxygen evolution reaction//hydrogen evolution reaction (OER// HER) systems. At 1.60 V, the HMFOR//NO₃⁻RR system achieved a maximum HMF conversion of 95.84%, an FDCA yield of 94.83%, and a FE of 89.53%, while at 1.90 V, it reached a maximum NH₃ yield of 32.50 mg h⁻¹ cm⁻² with an FE of 94.63%. This study underscores the catalytic advantages of heterogeneous interface engineering and provides a viable strategy for integrated biomass valorization and nitrogen-cycle remediation.</p>