Synergistic engineering of Cu doping and oxygen vacancies in ZnFe2O4 for efficient electrocatalytic nitrate reduction

The electrocatalytic nitrate reduction reaction (NO 3 RR) offers a sustainable route for nitrate-contaminated wastewater remediation and ammonia (NH 3 ) synthesis, yet its industrial implementation is bottlenecked by the lack of high-performance electrocatalysts. Spinel zinc ferrite (ZnFe 2 O 4 ) has emerged as a promising candidate due to its tunable electronic structure and robust chemical stability, but its catalytic potential is severely constrained by weak nitrate activation capability and insufficient active sites. Herein, we report a Cu-doped ZnFe 2 O 4 electrocatalyst synthesized via a solvothermal approach, wherein Cu doping in-situ induces the formation of oxygen vacancies (OVs), constructing a synergistic catalytic system. The OVs act as localized nucleophilic centers to strengthen NO 3 − adsorption, while adjacent Cu sites with upshifted d-band centers enhance electronic coupling with NO 3 − antibonding orbitals. This dual mediation optimizes reactant adsorption, promotes the breaking of N–O bonds, and reduces the energy barrier of the rate-determining step, thereby steering kinetics toward efficient NH 3 synthesis. As a result, under optimized conditions (−0.7 V vs. RHE, pH = 6, 1000 mg/L NO 3 − ), the catalyst achieves an NH 3 yield rate of 531.78 μg h −1 cm −2 , surpassing pristine ZnFe 2 O 4 by 52.08%. Furthermore, the electrochemical double-layer capacitance (C dl ) reaches 25.54 mF/cm 2 , substantially exceeding the 4.65 mF/cm 2 of the undoped sample and indicating a marked increase in active site density. This work demonstrates that the synergistic engineering of heteroatom doping and OV introduction is an effective strategy for designing high-performance NO 3 RR electrocatalysts, holding great potential for sustainable NH 3 synthesis and nitrate-contaminated wastewater remediation. • Cu-doped ZnFe 2 O 4 with oxygen vacancies was synthesized via a solvothermal approach. • Synergy between Cu dopants and oxygen vacancies enhances NO 3 − adsorption/activation and lowers the kinetic barrier. • The optimized ZnFe 2 O 4 -Cu 1% achieves a 52.08% enhanced NH 3 yield rate (531.78 μg h −1 cm −2 ). • The synergistic strategy provides a theoretical framework for designing efficient NO 3 RR electrocatalysts.