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

Abstract

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 CoO_x nanosheets (Co–B@CoO_x). In 100 ppm NO₃⁻–N, the Co–B@CoO_x 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 CoO_x catalysts. Furthermore, Co–B@CoO_x demonstrates an ultra-low energy consumption of 0.39 kW h mol_NO3⁻¹, 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@CoO_x originates from the formation of local nucleophilic/electrophilic regions at the Co–B/CoO_x Mott–Schottky interface, which effectively optimizes the targeted adsorption behavior of NO₃⁻ at the Co–B site and H₂O at the CoO_x site, thereby enhancing simultaneously NO₃⁻ affinity and active hydrogen availability. Furthermore, a novel Zn–NO₃⁻ battery utilizing the Co–B@CoO_x catalyst delivers a remarkable power density of 4.78 mW cm⁻², outperforming most recently reported Zn–NO₃⁻ batteries.