Performance and mechanism of ammonia production by electrocatalytic nitrate reduction based on dodecahydro-closo-dodecaborate hybrid

Abstract

Ammonia is an essential food and fertilizer component and is a fundamental raw material for industry and agriculture. In contrast, nitrate is the main pollutant that causes eutrophication in water. Electrocatalysis is a clean and efficient method for simultaneous nitrate removal and ammonia production. However, because ammonia production from the electrocatalytic nitrate reduction reaction (NO3RR) is a complex eight-electron process with slow kinetics, designing the cathode catalyst is critical for improving the ammonia yield. In this study, boron (B) doped metal oxides (TiZn2O4@B-x) obtained by coupling dodecahydro-closo-dodecaborate anions ([closo-B12H12]2−) and ZnTi-layered double hydroxides (ZnTi-LDH) after calcination was used as the cathode for the NO3RR. Specifically, TiZn2O4@B-700 exhibited excellent ammonia yield (21809.24 μg h−1 mgcat−1) and Faraday efficiency (FE) of (93.15%) at −1.8 V versus saturated calomel electrode (SCE). Furthermore, TiZn2O4@B-700 exhibited superior cycling stability and resistance to ionic interference. Moreover, density functional theory (DFT) calculations indicated that incorporating B increased the electron transfer rate and reduced the free energy required for the rate-limiting step of ammonia production via the NO3RR, thereby increasing the ammonia yield. This study provides a new concept for designing catalysts for green ammonia synthesis.