Promoting *NO2 Hydrogeneration on Cobalt-Doped Copper Oxides for Selective Ammonia Electrosynthesis from Nitrate

Electrochemical nitrate reduction reaction (NO₃RR) driven by renewable energy has attracted extensive attention, which can realize nitrate degradation and ammonia production simultaneously under ambient conditions. Copper−based catalysts are the most widely used due to their high activity but are subject to low selectivity owing to intermediate nitrite accumulation. This work has reported cobalt-doped copper oxide (Co/CuO) composites, while introduced Co sites accelerate the hydrogenation of nitrogen species. The prepared Co/CuO composites realize a 93.9 % Faradaic efficiency at the applied potential of −0.4 V (vs. RHE), yielding ammonia at 0.5441 mmol⋅h⁻¹ cm⁻². The exceptional stability of Co/CuO composites has also been affirmed by following continuous recycling tests. In situ characterization confirms that the existence of Co sites is prone to conversion of ^*NO₂ to ^*NH₂, thus exhibiting high performance for NO₃RR.