Dendritic copper oxide catalyst engineering weak-polarity Cu-O bond for high-efficiency nitrate electroreduction

Nitrate reduction reaction (NO₃RR) is deemed a promising pathway for both ammonia synthesis and water purification. Developing a high-efficiency catalyst with excellent NH₃ selectivity and catalytic stability is desirable but remains challenging. In this work, a dendritic copper oxide catalyst (Cu-B₂) has been developed to efficiently catalyze NO₃RR for ammonia production, the Cu-B₂ exhibits excellent catalytic performance, achieving an NH₃ Faradaic efficiency as high as 94 % and an NH₃ yield of 16.9 mg h^-1 cm^-2 with a current density of 192.3 mA cm^-2 at - 0.6 V (vs. RHE, reversible hydrogen electrode). During NO₃RR testing, the Cu-B₂ catalysts are reduced in situ to form highly active Cu⁰/Cu⁺ sites, while retaining its dendritic morphology. Compared with other catalysts, the Cu-O bond in Cu-B₂ catalyst has weaker polarity, resulting in Cu⁰/Cu⁺ sites in lower oxidation states. In situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies reveal the Cu-B₂ catalyst exhibits a potential-independent capability for *NO₃^- adsorption and high conversion efficiency of NO₂^- intermediate into ammonia, DFT calculations reveal that Cu-B₂ exhibts higher NO₃^- adsorption energy and lower NO₃^- adsorption energy barrier than Cu-B₁, thus endowing it with a remarkably improved catalytic activity and durability.