Review of carbon-based catalysts for electrochemical nitrate reduction and green ammonia synthesis

Electrochemical conversion of nitrate (NO3-) to ammonia (NH3) is a promising approach for removing NO3- contamination in water bodies as well as for producing NH3 necessary for agriculture. The electrochemical nitrate reduction reaction (NO3RR) uses renewable electricity as its energy source, operates under mild operating conditions, has low carbon emissions and is environmentally sustainable. Herein, we review the application of carbon-based electrocatalysts in NO3RR, including pure carbon materials, heteroatom doping or metal-bonding catalysts, and carbon substrate-supported composites. Fabrication methods, reaction pathways, mechanisms, experimental techniques and theory used in carbon-based electrocatalysts are critically analyzed and practical limitations are identified for industrial settings. Design aspects of catalyst structure are recommended for realizing NO3RR with carbon-based electrocatalysts and achieving clean and efficient large-scale production of green ammonia.