Tandem amorphization and bismuth-doping modulate the interfacial electronic structure of cobalt sulfide for efficient nitrate-to-ammonia electroreduction.

Abstract

Electrocatalytic nitrate reduction (NO3RR) offers a sustainable route for ammonia synthesis but is hampered by the competing hydrogen evolution reaction (HER) and sluggish intermediate conversion at the catalyst-electrolyte interface. Herein, we report an amorphous Bi-doped cobalt sulfide (a-Bi-CoS) catalyst that addresses these challenges via tandem structure-electronic regulation of Co sites. The amorphous framework promotes uniform Bi incorporation and abundant BiS bonds, reconfiguring the local coordination environment and surface charge distribution of Co. In situ Raman/FTIR spectroscopy and density functional theory calculations reveal that this tandem effect strengthens *NO adsorption, lowers the barrier of the rate-determining *NO → *NOH hydrogenation step, enhances water dissociation, and weakens *H binding. This tandem regulation kinetically favors protonation of nitrogen-containing intermediates and improves NO3RR selectivity. Consequently, a-Bi-CoS achieves a Faradaic efficiency of 94.3% and an NH3 yield of 18.02 mg h-1 cm-2 at -0.5 V vs. RHE. Integrated into a membrane electrode assembly flow reactor coupled with glycerol oxidation, it delivers a stable NH3 production rate of 23.58 mg h-1 cm-2 over 40 h, highlighting its great potential for practical electrochemical ammonia synthesis.