Co-Ni bimetallic oxide with tuned surface oxygen vacancies efficiently electrocatalytic reduction of nitrate to ammonia.

The electrocatalytic reduction reaction of nitrate (NO) to ammonia (NH) provides an efficient and clean NH production method, which has the potential to replace the traditional industrial preparation methods. However, the limited activity and Faraday efficiency (FE) of existing catalysts impede the practical application of this technology. Herein, in this work, a high-performance catalyst with high NH yield and FE was fabricated. Co-Ni bimetallic oxide (NiCoO) catalysts with tuned surface oxygen vacancies (OVs) contents were prepared by changing the heating rate during calcination, NiCoO calcined at a heating rate of 5 °C/min (NiCoO-5) possessed the highest surface OVs content. Experimental studies showed that NiCoO with higher surface OVs had better NORR activity, inhibited the production of nitrite (NO), and exhibited higher selectivity to NH. Among prepared catalysts, NiCoO-5 demonstrated superior performance in electrocatalytic reduction of NO to NH, achieving a high NH FE (94.4 %) and yield (193.2 mmol/h g) at a suitable applied voltage. Besides, in situ Fourier transform infrared spectroscopy analysis suggested that NiCoO-5 preferentially followed the NORR pathway as follows: *NO → *HNO → *NO → *HNO → *NO → *HNO → *N → *NH → *NH → *NH.