Electrochemical ammonia synthesis: fundamental practices and recent developments in transition metal boride, carbide and nitride-class of catalysts

Abstract

Ammonia, a value-added chemical, major fertilizer and future transportation fuel, is conventionally and synthetically produced by the energy intensive Haber–Bosch process. For the conversion of nitrogen to ammonia, more energy efficient and environmentally friendly approach is required which can be fulfilled by the electrochemical nitrogen reduction reaction (NRR). Because of its sluggish kinetics and poor selectivity, the progress of NH₃ production is far beyond the industrial periphery. So, to meet the current energy demands, here we have summarized the bottlenecks of the NRR and have discussed briefly how to overcome these issues in terms of competitive HER, N₂ solubility in the electrolyte, and material specificity. Among the various categories of catalysts explored for NRR, we are here interested in transition metal borides (Mbenes), carbides (TMCs) and nitrides (TMNs) because of their respective benefits in selective N₂ adsorption and its subsequent reduction. We have widely covered the DFT studies concerning these catalysts and their experimental implementations towards NRR. Along with that, we believe that this review with detailed fundamentals of N₂ reduction will act as a tutorial for new-comers in this field. Finally, with the focus on the current challenges in this field, potential opportunities and future prospective have been provided.