Self-enhanced localized alkalinity at the encapsulated Cu catalyst for superb electrocatalytic nitrate/nitrite reduction to NH3 in neutral electrolyte

Abstract Electrocatalytic nitrate/nitrite reduction reaction (eNOx−RR) to NH3 is thermodynamically more favorable than the eye-catching N2 electroreduction, showing wide application scenarios. To date, the high catalytic activity for eNOx−RR-to-NH3 is limited to strong alkaline electrolytes, but cannot be achieved in economic and sustainable neutral/near-neutral electrolytes. Herein, we construct a novel Cu catalyst which is encapsulated inside the hydrophilic hierarchical nitrogen-doped carbon nanocages (Cu@hNCNC). During eNOx−RR, the hNCNC shell hinders the diffusion of generated OH− ions to the outside of hNCNC, and thus creates a self-enhanced local high pH environment around the inside Cu nanoparticles, which is supported by the experimental results and finite element simulations. Consequently, the Cu@hNCNC catalyst exhibits an excellent eNOx−RR-to-NH3 activity even in neutral electrolyte, equivalent to the Cu catalyst immobilized on outer surface of hNCNC (Cu/hNCNC) in strong alkaline electrolyte, with much better stability for the former. In the neutral electrolyte with 1 mol L−1 NOx−, Cu@hNCNC catalyst exhibits a record-high NH3 yield rate up to 4.0 mol h−1 g−1 with high Faradaic efficiency of 99.7%. The strong-alkalinity-free advantage suggests the potential application, and the practicability of Cu@hNCNC catalyst is demonstrated in a coupled plasma-driven N2 oxidization with eNOx−RR-to-NH3 process. This study presents an advanced approach to high-efficient eNOx−RR-to-NH3 in neutral/near-neutral electrolytes with scientific and technological significance, and even beyond.