Copper–Nickel Oxide Nanosheets with Atomic Thickness for High‐Efficiency Sulfur Ion Electrooxidation Assisted Nitrate Electroreduction to Ammonia

Abstract The nitrate electroreduction reaction (NO₃RR) offers an eco‐friendly alternative to the Haber–Bosch technology for ammonia (NH₃) synthesis. However, the complex reaction process and diverse products make efficient NH₃ synthesis challenging. Therefore, the rational design and preparation of highly efficient electrocatalysts are crucial for NO₃RR. Herein, ultrathin copper‐nickel oxide (Cu‐NiO) nanosheets (Cu‐NiO UTNSs) are synthesized via the cyanogel‐NaBH₄ hydrolysis‐reduction method, which are applied for the cathodic NO₃ RR to NH₃‐assisted with the anodic sulfur ion (S²⁻) oxidation reaction (SOR) in an electrolyzer. The ultrathin nanosheet structure, the interaction between NiO and Cu, and the formation of oxygen vacancy contribute to generating the rich active sites, regulating the electronic structure, and improving the substance adsorption. Thus, the Cu‐NiO UTNSs exhibit excellent electrocatalytic performance for NO₃RR and SOR. As a bifunctional Cu‐NiO UTNSs||Cu‐NiO UTNSs electrolyzer, it can reach 10 mA cm⁻¹ at only 0.1 V for NO₃⁻‐to‐NH₃ conversion at the cathode and S²⁻‐to‐S₈ conversion at the anode. This work provides a promising approach for producing value‐added chemicals at a low electrolysis voltage and a strategy for pollutant treatment.