Electrocatalytic Reduction of Nitrate to Ammonia on Low-Cost Ultrathin CoOx Nanosheets

The electrochemical nitrate reduction reaction (NITRR) is an appealing method for ammonia synthesis, owing to the ambient conditions as well as its abundant sources, low dissociation energy, and high solubility of nitrate. The hydrogen evolution reaction is a competing process of the NITRR, which should be properly suppressed to achieve a high Faradaic efficiency of the NITRR. Herein, ultrathin CoOx nanosheets with abundant surface oxygen are designed as a low-cost NITRR catalyst, which delivers an ultrahigh ammonia yield of 82.4 ± 4.8 mg h–1 mgcat–1 with a Faradaic efficiency of 93.4 ± 3.8% at −0.3 V versus the reversible hydrogen electrode. Theoretical calculation reveals that the surface oxygen on cobalt sites can stabilize the adsorbed hydrogen on cobalt oxide, which hampers the evolution of hydrogen and leads to an enhanced NITRR activity. This work demonstrates that surface modification plays a critical role in suppressing the HER and facilitating the NITRR through a NHO pathway with a lower energy barrier.