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Electrochemical techniques have shown advantages for the removal of low-concentration nitrate. Here, copper oxide nanosheets were grown on self-supporting nickel foam (NF) to prepare electrodes (CuO/NF), which realized the rapid and highly selective conversion of nitrate pollutants in sewage into nontoxic and harmless N2. The CuO/NF afforded 100% NO3– removal within 100 min and 99.53% selectivity for N2 at –50 mA without producing a lot of by-products (NO2–, NH4+, and N2H4). Furthermore, 81.8% of NO3– was removed under the given conditions after six experimental repetitions. These results suggest that the catalyst has excellent electrochemical stability. The performance of CuO/NF for the electrocatalytic removal of NO3– in simulated wastewater (which contained Cl– and SO42–) was almost unaffected. Because of the high efficiency, high stability, and low cost of CuO/NF, this catalyst is practical for the removal of nitrate for wastewater purification.