Mott-Schottky contact synergistically boosts the electroreduction of nitrate to ammonia under low-nitrate concentration

The electrocatalytic nitrate reduction reaction (NO3RR) holds tremendous potential for remediating NO3- pollution in groundwater and obtaining clean ammonia (NH3). However, the currently reported NO3RR catalysts face challenges in achieving high conversion efficiency at low NO3- concentrations due to sluggish reaction kinetics. Herein, we present a highly efficient Mott-Schottky electrocatalyst, composed of an amorphous Co-B nanochain embedded in amorphous CoOx nanosheets (Co-B@CoOx). In 100 ppm NO3--N, the Co-B@CoOx catalyst exhibits remarkable performance, achieving over 95% NO3- removal within 40 min at -0.90 V vs. reversible hydrogen electrode and nearly 100% NH3 selectivity at -0.80 V, surpassing the performance of both Co-B and CoOx catalysts. Furthermore, Co-B@CoOx demonstrates an ultra-low energy consumption of 0.39 kW h molNO3-1, establishing it as one of the most active catalysts available. Comprehensive experimental investigations and theoretical calculations indicate that the high conversion efficiency of Co-B@CoOx originates from the formation of local nucleophilic/electrophilic regions at the Co-B/CoOx Mott-Schottky interface, which effectively optimizes the targeted adsorption behavior of NO3- at the Co-B site and H2O at the CoOx site, thereby enhancing simultaneously NO3- affinity and active hydrogen availability. Furthermore, a novel Zn-NO3- battery utilizing the Co-B@CoOx catalyst delivers a remarkable power density of 4.78 mW cm-2, outperforming most recently reported Zn-NO3- batteries. A Mott-Schottky electrocatalyst composed of amorphous Co-B nanochain embedded in amorphous CoOx nanosheets was developed for highly efficient conversion of NO3--to-NH3.