Fabrication of dual-sited Cu doped Co3O4 on nickel foam (Cu–Co3O4/NF) for segmentally efficient electrochemical nitrate reduction under low conductivity†

To tackle the removal of low-concentration nitrate contamination, this work utilizes electrocatalytic reduction technology to effectively convert nitrate into recoverable ammonia, using as-prepared Cu doped Co₃O₄ on nickel foam (Cu–Co₃O₄/NF) composites as the cathode. This electrode demonstrated exceptional electrocatalytic activity in simulated groundwater with low nitrate concentrations and low conductivity (around 3000 μS cm⁻¹). With the simulated groundwater containing 50 mg L⁻¹ of nitrate nitrogen, the electrode achieved a removal efficiency of 96.78% within 2 hours, with ammonia nitrogen selectivity reaching 97.58%. Moreover, the nitrate removal rate remained stable above 95% even after nine consecutive cycles of operation, indicating the reliability and stability of the fabricated dual-sited Cu–Co₃O₄/NF cathode. Finally, it was demonstrated that Cu doping could reduce the RDS (*NO → *NOH) thermodynamic energy barrier, and then optimize the eNO₃RR pathway through DFT computation. Therefore, this work offers an economically viable, efficient, and sustainable solution for the remediation of low-concentration nitrate-contaminated groundwater, through circumventing additional costs and secondary pollution risks associated with the use of electrolytes.