Enhanced electrochemical nitrate reduction with a novel (Mn,Fe)2O3/Co3S4 electrocatalyst for sustainable ammonia production

This study presents a novel (Mn,Fe) 2 O 3 /Co 3 S 4 composite catalyst designed for electrochemical nitrate reduction reaction (NO 3 - RR) to overcome challenges in sustainable ammonia production and potentially replace the energy-intensive Haber-Bosch process. The ternary (Mn,Fe) 2 O 3 /Co 3 S 4 composite catalyst exhibited outstanding performance, achieving a high ammonia (NH 3 ) yield rate of 17.54 mg.h −1 cm −2 and an impressive Faradaic efficiency of 95.5 % at −0.3 V vs. RHE, with stable durability in alkaline condition. This performance surpasses the NH 3 yield rate of the S-free MnFeCo(3:1:1) ternary catalyst and the binary MnFe(31:1) catalyst by 1.6 and 5.3 times, respectively. This enhanced performance was accredited to the abundant cation and anion defects with multiple valence charges of (Mn, Fe) 2 O 3 /Co 3 S 4 catalyst, which were introduced by inserting a third metal of Co and the nonmetal of S into a binary MnFe system. The proposed mechanism for NO 3 - RR indicates that oxygen vacancies , combined with the multiple valance charges of the (Mn,Fe) 2 O 3 /Co 3 S 4 phase, enable effective nitrate adsorption and H 2 O dissociation. This interaction boosts NO 3 - RR performance, resulting in a notable NH 3 yield rate and Faradaic efficiency. This research opens a promising new opportunity for the rational strategy and future research for introducing third metal and nonmetal-oxide/sulfide electrocatalysts to realize the critical need for alternative NH 3 production.