Defect engineering toward binary spinel ZnCo2O4 for boosting electrocatalytic nitrate reduction to ammonia

Abstract

Electrochemical nitrate reduction reaction (NO3 −RR) has a significant application potential for the electrochemical synthesis of ammonia at ambient temperature. Spinel oxides have garnered an extensive attention as effective electrocatalysts for NO3 −RR due to their flexible ion arrangements multiple oxidation states and high electrical conductivity. A defect-engineering approach using alkaline electrochemical etching on ZnCo2O4 electrocatalyst was employed to creat a mass of Zn vacancies in crystal lattice (VZn-ZnCo2O4). This not only induces lattice distortion, but also reduces the charge transfer resistance and optimizes the internal electron transportation. It achieved a maximum NH3 Faradaic efficiency (FENH3) of 94.5 % and NH3 yield rate of 2.79 mg h−1 cm−2 in 0.1 M NO3 −. Even in a dilute nitrate solution of 0.01 M NO3 −, the FENH3 still reaches a maximum of 91.74 % at −0.5 V, with an NH3 yield rate of 1.62 mg h−1 cm−2. Zn defects can accumulate abundant electrons in the highest occupied molecular orbital (HOMO) and shorten the CoO bond length with NO3 − adsorption, thereby promoting NO3 − adsorption. The surface Zn atomic defects suppress the HER and lower the energy barrier of the rate-determining step (RDS) from 0.44 eV to 0.24 eV, significantly enhancing the activity and selectivity of NO3 −RR. © 2025 Elsevier B.V.