Efficient and selective electroreduction of nitrate to ammonia via interfacial engineering of B-doped Cu nanoneedles

Abstract

Electrocatalytic nitrate reduction to ammonia is a promising method to mitigate nitrate contamination and produce valuable chemical. However, it still suffers from slow active hydrogen (*H) transfer kinetics and unfavorable thermodynamics. Here the *H transfer and reaction energy barrier of nitrate reduction reaction were regulated on B-doped Cu nanoneedles (Cu NNs-B) to enhance ammonia electrosynthesis via interfacial engineering. The high-curvature nanoneedles showed locally enhanced electric fields, which promoted *H supply from water dissociation. B-doping provided Cu/Cu active sites for the activation of nitrate and intermediates. Due to the simultaneously improved *H supply kinetics and reaction thermodynamics, Cu NNs-B was efficient for reducing nitrate to ammonia, achieving high Faradaic efficiencies (FEs) of 95.1–98.6 % and ammonia yields of 0.12–1.33 mmol·h·cm at 50–1500 mg·L NO-N. Nitrate was selectively converted to ammonia with the remaining nitrate and nitrite concentrations below drinking water standards. Experimental and DFT results revealed Cu NNs-B with properly higher nanotip curvature was more favorable for boosting ammonia electrosynthesis from both kinetics and thermodynamics.