Metal-based electrocatalysts for ammonia electro-oxidation reaction to nitrate/nitrite: Past, present, and future

Electrocatalytic oxidation of ammonia is an appealing, low-temperature process for the sustainable production of nitrites/nitrates that avoids the formation of pernicious N2O and can be fully powered by renewable electricity. However, the number of known efficient catalysts for this purpose is limited. In this review, based on the possible reaction mechanism of electrocatalytic ammonia oxidation reaction (AOR), the control of catalyst performance by hybrid composite design, microstructure construction, and surface modification is reviewed, and the prospects of AOR catalysts for photocatalysis, thermocatalysis, and biocatalysis are proposed. Notably, a rational and rigorous AOR experimental protocol is suggested. We hope that the research community will jointly focus on the sensible testing of AOR products and eventually develop a more realistic evaluation system. Finally, a techno-economic analysis of AOR electrocatalysis was carried out, and a more economical carbon-free cycle system based on the AOR process was proposed.