Electrocatalytic conversion of nitrate to ammonia on the oxygen vacancy engineering of zinc oxide for nitrogen recovery from nitrate-polluted surface water.

Nitrate pollution in surface water poses a significant threat to drinking water safety. The integration of electrocatalytic reduction reaction of nitrate (NORR) to ammonia with ammonia collection processes offers a sustainable approach to nitrogen recovery from nitrate-polluted surface water. However, the low catalytic activity of existing catalysts has resulted in excessive energy consumption for NORR. Herein, we developed a facile approach of electrochemical reduction to generate oxygen vacancy (Ov) on zinc oxide nanoparticles (ZnO NPs) to enhance catalytic activity. The ZnO NPs achieved a high NH-N selectivity of 92.4% and NH-N production rate of 1007.9 [Formula: see text] h m at -0.65 V vs. RHE in 22.5 mg LNO-N, surpassing both pristine ZnO and the majority of catalysts reported in the literature. DFT calculations with in-situ Raman spectroscopy and ESR analysis revealed that the presence of Ov significantly increased the affinity for the NO (nitrate) and key intermediate of NO (nitrite). The strong adsorption of NO on Ov decreased the energy barrier of potential determining step (NO →∗NO) from 0.49 to 0.1 eV, boosting the reaction rate. Furthermore, the strong adsorption of NO on Ov prevented its escape from the active sites, thereby minimizing NO by-product formation and enhancing ammonia selectivity. Moreover, the NORR, when coupled with a membrane separation process, achieved a 100% nitrogen recycling efficiency with low energy consumption of 0.55 kWh mol at a flow rate below 112 mL min for the treatment of nitrate-polluted lake water. These results demonstrate that ZnO NPs are a reliable catalytic material for NO₃RR, enabling the development of a sustainable technology for nitrogen recovery from nitrate-polluted surface water.