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.