Recent Development of Catalysts for the Nitrate Reduction Reaction: Electrochemical Solution to Produce Ammonia

Ammonia, essential for agriculture fertilizers and as an energy carrier, is traditionally produced by the energy-intensive Haber-Bosch process, which is a significant energy consumer and a notable contributor to CO2 emissions. The electrochemical nitrate reduction reaction (NO3RR) to produce ammonia presents a promising and environmentally friendly solution, allowing to reduce NO3- contamination in waste water resources. This review covers recent trends in noble and non-noble metal-based catalysts, single-atomic metal catalysts, and metal-free catalysts for NO3RR. Specifically, it was found that transition metals were effective in enhancing electron transfer in the NO3RR due to their d-orbital energy levels. Furthermore, alloys or single atomic catalysts with transition metals have been studied to improve NO3RR performance by adjusting the crystal plane or generating oxygen vacancies. Metal-free catalysts have been investigated and have exhibited great potentials in the NO3RR. It was revealed that tuning the electronic properties can effectively suppress the side reactions and increase the ammonia yield and Faradaic efficiency. This review aims to provide guidance for catalyst design and performance improvement in future NO3RR research.