Self-enhanced localized alkalinity at the encapsulated Cu catalyst for superb electrocatalytic nitrate/nitrite reduction to NH 3 in neutral electrolyte

Abstract

The electrocatalytic nitrate/nitrite reduction reaction (eNO x − RR) to ammonia (NH 3 ) is thermodynamically more favorable than the eye-catching nitrogen (N 2 ) electroreduction. To date, the high eNO x − RR-to-NH 3 activity is limited to strong alkaline electrolytes but cannot be achieved in economic and sustainable neutral/near-neutral electrolytes. Here, we construct a copper (Cu) catalyst encapsulated inside the hydrophilic hierarchical nitrogen-doped carbon nanocages (Cu@hNCNC). During eNO x − RR, the hNCNC shell hinders the diffusion of generated OH − ions outward, thus creating a self-enhanced local high pH environment around the inside Cu nanoparticles. Consequently, the Cu@hNCNC catalyst exhibits an excellent eNO x − RR-to-NH 3 activity in the neutral electrolyte, equivalent to the Cu catalyst immobilized on the outer surface of hNCNC (Cu/hNCNC) in strong alkaline electrolyte, with much better stability for the former. The optimal NH 3 yield rate reaches 4.0 moles per hour per gram with a high Faradaic efficiency of 99.7%. The strong-alkalinity-free advantage facilitates the practicability of Cu@hNCNC catalyst as demonstrated in a coupled plasma-driven N 2 oxidization with eNO x − RR-to-NH 3 .