Mechanisms of electrochemical nitrogen gas reduction to ammonia under ambient conditions: a focused review

Electrocatalytic nitrogen reduction reaction (E-NRR) to ammonia is becoming a major topic of interest in the field of large-scale energy storage from renewable sources and water. This approach is considered as an alternative route of ammonia production that could replace the high energy demanding and polluting Haber-Bosch process or high pressure stored hydrogen from electrolysis. This focused review covers different recent aspects of ammonia production via E-NRR electrocatalysis, including the challenges of E-NRR, reaction mechanisms, different materials of E-NRR catalysts such as noble metal-based, non-noble transition metal-based oxides, nitrides, carbides, and hetero-atom-based catalysts, emphasizing bifunctional catalysts reacting at ambient pressures and temperatures, which were not included in previous reviews. In addition, we discuss important issues concerning the commonly used experimental setup, testing protocols, and various NH3 quantification methods. The various fundamental and applied research methodologies summarized in this review can serve to promote efficient research on electrocatalytic nitrogen reduction and ammonia production, making it a promising future energy storage as a synthetic alternative fuel.