Exclusive nitrate to ammonia conversion via boron-doped carbon dots induced surface Lewis acid sites

Abstract

Electrocatalytic nitrate reduction represents a very promising route for ammonia synthesis under ambient conditions. However, for most nitrate-to-ammonia electrocatalysts developed to date, the Faradaic efficiency (FE) to ammonia is modest due to the competitive hydrogen evolution reaction (HER). Here, we report that the decoration of vertically aligned NiCo2O4 pillars with boron-doped carbon dots (BCDs) enables electrocatalytic nitrate reduction to ammonia with ∼100% FE. A BCDs/NiCo2O4/carbon cloth cathode delivers a NH3 production rate of 173.9 μmol h−1 cm−2 at −0.55 V versus reversible hydrogen electrode (RHE). This state-of-the-art performance is linked to the BCDs, which provide an abundance of Lewis acid sites on the electrocatalyst surface for the adsorption of nitrate ions (simultaneously suppressing the competitive HER). This work reveals that highly selective NH3 electrosynthesis can be achieved under ambient conditions by regulating the surface acidity/basicity properties of metal-oxide-based catalysts, paving the way toward more sustainable NH3-production technologies.