Oxygen vacancies-rich CoMoO4 nanosheets facilitate the electroreduction of nitrite to ammonia

Electrocatalytic reduction is a promising method to remove NO2−; not only can it deal with environmental issues, but it can also recycle NO2− to form NH3. This study involved the preparation of oxygen vacancies-rich monoclinic cobalt molybdate nanosheets on nickel foam (CoMoO4/NF) employing a hybrid approach of hydrothermal and calcination reduction techniques renders highly effective catalysts for electroreduction of nitrite (NO2−RR). The presence of oxygen vacancies increases carrier density, enhancing electrical conductivity, reducing resistance, and accelerating electron transfer. Additionally, it serves as an active site for absorbing NO2−. In an aqueous solution containing 0.5 M Na2SO4 and 0.1 M NO2−, the Faraday efficiency (FE) of CoMoO4/NF reaches an impressive 98.6 ± 0.02 % at −0.8 V vs. RHE, and NH3 yield demonstrates a commendable performance, attaining 32.72 ± 0.17 mg/h cm−2. Meanwhile, it exhibits robust and enduring characteristics throughout the stability tests. Employing CoMoO4/NF as the cathode, the Zn − NO2− battery demonstrates a peak power density of 5.94 mW cm−2 alongside an NH3 yield of 3.88 mg/h cm−2 and an FE of 91.88 %. Furthermore, density functional theory calculations uncover the significant influence of oxygen vacancies on enhancing nitrite adsorption and activation over the CoMoO4 surface and bring to light possible reaction pathways.