Investigating the role of oxygen vacancies in metal oxide for enhanced electrochemical reduction of NO₃⁻ to NH₃: mechanistic insights

Ammonia (NH₃) is a crucial chemical commodity used extensively in fertilizer production and as a renewable potential energy carrier. Conventionally, NH₃ synthesis relies on the energy-intensive Haber-Bosch process, which requires elevated temperatures and pressures. However, the demanding conditions of this method have led to research into electrochemical NH₃ synthesis via nitrate (NO₃⁻) and water, creating a sustainable environment. The electrochemical nitrate reduction reaction (NO₃RR) emerged as a promising eco-friendly alternative, boasting reduced energy consumption and mild reaction conditions. Moreover, the NO₃RR is capable of achieving a high NH₃ yield and faradaic efficiency (FE) but poses challenges due to the competing hydrogen evolution reaction (HER), etc. To address these issues, it is essential to tailor the structure of the electrocatalysts, such as incorporating oxygen vacancies (OVs) and controlling the coordination environment and local electronegativity. This review offers a thorough description of current developments in the identification, processing, and use of OVs for the NO₃RR. We highlight different OV generation processes and the associated assessment methodologies. Lastly, we discuss the challenges and opportunities of designing metal oxide catalysts with OVs for NO₃RR, aiming to accelerate the development of exceptional electrocatalysts and contribute to a sustainable future for ammonia generation.