Copper-modified nickel membrane reactor for electrochemical hydrogenation in low-conductivity water

Electrochemical hydrogenation (ECH) for wastewater treatment is often limited by its reliance on high-conductivity media, restricting applications such as nitrate-contaminated groundwater remediation. Here we show that a copper-modified electrochemical nickel membrane reactor (Cu/eNMR) can remove nitrate from deionized water. For water containing 50 mg/L NO3−-N, Cu/eNMR achieves 90.5% nitrate removal at 5 mA/cm2 within 3 h, with an energy consumption of 0.139 kWh/g-N, compared with 12.8% removal and 8.6 kWh/g-N for a conventional reactor using the same cathode. Mechanistic analysis reveals that nitrate hydrogenation is enabled by direct electron transfer to the reaction chamber, coupled with directional K+ migration that maintains charge neutrality, while interfacial charge-transfer resistance governs electron-flow direction. The membrane configuration also suppresses anodic side reactions, including active chlorine formation, chlorinated by-products, organic polymerization and metal-induced anode deactivation. Solar-powered treatment of real groundwater further demonstrates practical applicability, while life-cycle analysis indicates reduced greenhouse-gas emissions compared with conventional electrochemical and biological treatments. This architecture broadens the feasible application of ECH to low-conductivity water treatment. Electrochemical hydrogenation is promising for water remediation yet limited by high energy use in poorly conductive media. Here, the authors report a copper-modified nickel membrane reactor for energy-efficient nitrate removal from low-conductivity water.