Recent progress in the development of electrocatalysts for the electrochemical N-2 reduction reaction

Ammonia is the second-most produced chemical throughout the world to maintain the global food supply and other chemical stocks. The annual worldwide ammonia production is currently more than 200 million tons through the Haber-Bosch process, which consumes an enormous amount of energy due to the requirement of high pressure (>10 MPa) and relatively high temperature (400-500 degrees C). In recent years, electrochemical N-2 reduction reaction (ENRR) under ambient conditions has received paramount attention in the scientific community. However, large-scale production of ammonia from the ENRR is limited by the lack of efficient cost-effective catalysts. The success of ENRR firmly depends on the efficiency of the electrocatalyst in a suitable electrolyte. However, identification and generation of the active sites in the electrocatalysts for ENRR remain elusive, impeding the development of the catalysts. In this review article, recent progress made in the development of efficient electrocatalysts for ENRR under ambient conditions is focused on with special attention on the physicochemical properties and active sites of the catalyst towards the NH3 production rate by considering experimental as well as theoretical aspects. This review elaborates on key aspects for the development of an efficient and stable electrocatalyst for NH3 production. In addition, the role of electrolytes and different sources of errors in the ENRR measurement for NH3 production are outlined briefly.