High-efficiency ammonia electrosynthesis via selective reduction of nitrate on ZnCo2O4 nanosheet array

Abstract

Electrochemical nitrate (NO3−) reduction reaction is highly encouraging for environmental NO3− contaminant removal and has emerged as an energy-efficient and environment-friendly NH3 synthesis route under mild conditions. This aqueous NO3− reduction process, however, not only suffers from strong competition from hydrogen evolution reaction (HER) but simultaneously generates unwanted side products, highlighting the great significance of exploring efficient catalysts for NH3 production. Here, a ZnCo2O4 nanosheet array supported on carbon cloth (ZnCo2O4 NSA/CC) acts as a superb 3D catalyst toward highly active and selective electrohydrogenation of NO3− to NH3. In 0.1 M NaOH with 0.1 M NaNO3, such catalyst attains a superior Faradaic efficiency of 98.33% at −0.6 V vs. reversible hydrogen electrode (RHE) and a large NH3 yield of 634.74 μmol h−1 cm−2 at −0.8 V vs. RHE, with excellent durability. Remarkably, a Zn–NO3− battery with ZnCo2O4 NSA/CC cathode achieves a power density of 4.62 mW cm−2 and an NH3 yield of 91.75 μmol h−1 cm−2, superior to the previously reported Zn–NO3− battery. Theoretical calculations reveal that ZnCo2O4 (311) surface severely inhibits HER and is highly active for NO3− reduction with a potential determine step of 0.29 eV.