Synergistic effect of oxygen vacancies and oxygen-bridged multi-interface sites for high-performance electrocatalytic nitrate reduction to ammonia

Abstract In recent years, the development of highly efficient electrocatalysts for the nitrate reduction reaction (NO3RR) to ammonia (NH3) has become essential for achieving sustainable nitrogen cycling. Herein, a sea urchin-like CuNiO with oxygen vacancies (Vo-CuNiO) was synthesized via a gas-assisted solvothermal method followed by calcination. This unique hierarchical architecture facilitates the formation of abundant oxygen vacancies and optimizes the adsorption of key intermediates, while the exposure of oxygen-bridged multi-interface sites (such as Cu–O–Cu, Ni–O–Ni, and Cu–O–Ni interfacial sites) enhances mass transport. The obtained Vo-CuNiO-350 catalyst exhibited exceptional performance in the electrocatalytic NO3RR to NH3 under neutral conditions, achieving a peak NH3 Faradaic efficiency (FE) of 94.9% at −0.8 V vs. reversible hydrogen electrode (RHE) and a maximum NH3 yield rate of 480.9 μmol·h−1·cm−2 at −1.0 V vs. RHE. In-situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and density functional theory (DFT) calculations indicated that the oxygen vacancies and bimetallic interface sites in the Vo-CuNiO-350 catalyst provide a synergistic effect to enhance NO3RR performance. Specifically, the oxygen vacancies and the newly constructed Cu–O–Ni interface sites optimize the adsorption of intermediates and promote the reduction of NO3− to NH3. The further continuous electrocatalytic NH3 synthesis tests indicate that this catalyst can achieve high-purity NH4Cl production at a rate of 14.0 mg·h−1. Moreover, in a self-assembled Zn-NO3− hybrid battery, an output power density of 2.88 mW·cm−2 was attained, thereby enabling simultaneous electricity generation and NH3 synthesis. This work demonstrates a viable pathway for converting nitrate from wastewater into ammonia while co-producing electrical energy.