Progress of electrochemical synthesis of nitric acid: catalyst design, mechanistic insights, protocol and challenges

Nitrogen-based fertilizers are necessary to increase the agricultural output since fixed nitrogen is often the limiting factor for plant growth. The main ingredients in almost all nitrogen-based fertilizers are ammonia and nitric acid; demand for these substances is significantly driven by global population and food production. Over the next few decades, the size and value of the ammonia and nitric acid markets will continue to be largely influenced by the global population, which will have a significant impact on energy utility. Ammonia is synthesized via the energy intensive Haber-Bosch process, and in the Ostwald process, ammonia is catalytically oxidized to produce industrial grade nitric acid. Commercial production of nitric acid requires astronomical amounts of energy, and as a consequence emits greenhouse gases into the atmosphere at an alarming rate. As the process of manufacturing industrial nitric acid uses huge amounts of energy and emits greenhouse gases into the atmosphere, it is an absolute necessity to find an alternative route of nitric acid synthesis. In the approaching century, the most advantageous method that has the potential to significantly alter human lifestyle is the electrochemical production of nitrate/nitric acid by nitrogen oxidation. In this review article, we have discussed the design of catalysts, mechanistic insights and the strategy adopted for the electrochemical nitrogen oxidation reaction (N2OR). Emphasis has been put on the various challenges that exist during the N2OR and the possible solutions to overcome the hurdles.