Reduced spinel oxide ZnCo2O4 with tetrahedral Co2+ sites for electrochemical nitrate reduction to ammonia and energy conversion

Electrocatalytic NO3− reduction to ammonia (NRA) at ambient conditions emerges as an appealing solution for green ammonia synthesis. In this work, we prepared a reduced Co-based spinel oxide for efficient ammonia synthesis and energy conversion. The in-depth structural characterization and electrochemical evaluation revealed that the introduction of Zn and reduction treatment led to the formation of electron-deficient tetrahedrally coordinated Co2+ sites. The resulting R-ZnCo2O4 exhibited remarkable NH3 production capacity with high NH3 selectivity of 92.2 %, FE of 92.3 %, and yield rate of 5.35 mgNH3 h−1 cm−2 (ca. 26.75 mgNH3 h−1 mgcat−1) under a low potential of − 0.3 V vs. RHE. The NRA pathway on R-ZnCo2O4 was further elucidated through DFT calculations and in situ characterizations. The high NRA efficiency of R-ZnCo2O4 was further explored in a Zn − NO3− battery, which was specified by an open circuit voltage of 1.46 V and a peak-power density of 1.40 mW cm−2, demonstrating its promising application for sustainable energy supply and green ammonia synthesis.