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

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 .