Electrocatalytic Reduction of Nitrate to Ammonia in an Aqueous Environment Using Nanoporous N- and P-Enriched Carbonaceous Material

Carbonization (Argon atmosphere, 900 °C, 2 h) of heteroatom-enriched pyridine-bridged inorganic-organic hybrid material (HPHM) resulted in the formation of a high specific surface area (SA_BET of 1080 m² g^-1) carbonaceous material designated as HPHMC900. The HPHMC900 serves as an effective electrocatalyst for the reduction of nitrate in an aqueous environment to ammonia (NO₃RR). Importantly, HPHMC900 demonstrated fast kinetics for the NO₃RR with a low Tafel slope of 70 mV decade^-1. An NH₃ production yield of 21 μg h^-1 mg_cat^-1 was obtained with a Faradaic efficiency (FE) of 88.3% at -0.4 V in a 0.1 M KNO₃ electrolytic solution. The high double layer capacitance (<i>C</i>_dl) of 14.1 mF cm^-2 corroborates high SA_BET and exposed active sites of HPHMC900. The maximum FEs were estimated to be 48%, 93%, and 98%, corresponding to 0.05, 0.5, and 1.0 M KNO₃ with maximum NH₃ production yields of 18.7, 22.1, and 39.0 μg h^-1 mg_cat^-1, respectively. The potential of employing HPHMC900 for the NO₃RR as an electrocatalyst is evident by its robust stability, high SA_BET, and enrichment with heteroatoms N (7.7%) and P (0.28%). Thus, this sustainable environmentally benign strategy can be used for the treatment of pollutant NO₃^- to produce NH₃.