Atomically Dispersed Cobalt on Ionic Carbon Nitrides for Selective and Efficient Nitrate Electroreduction to Ammonia

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical conversion of nitrate to ammonia offers sustainable production and pollution mitigation.
• Carbon nitrides (CNs) are promising catalyst supports but face conductivity and stability challenges.
• Conventional CNs limit efficiency in nitrate reduction due to poor charge transport and metal site stabilization.

Purpose of the Study:

• To develop a novel carbon nitride material for enhanced electrochemical nitrate-to-ammonia conversion.
• To overcome the limitations of conventional CNs in terms of electrical conductivity and active site stabilization.
• To investigate the catalytic performance and mechanism of the new material for selective ammonia synthesis.

Main Methods:

• Synthesis of cobalt poly(heptazine imides) (CoPHI) with coordinated Co2+ active sites.
• Electrochemical characterization including Faradaic efficiency and yield rate measurements.
• Density functional theory (DFT) calculations and experimental studies to elucidate the reaction mechanism.

Main Results:

• CoPHI exhibits a high density of isolated Co active sites (1.092 wt.%) with enhanced charge transport.
• Achieved 93.5% Faradaic efficiency and a high NH3 yield rate of 46.1 mg·h-1·mgcat.-1 at -0.8 V vs RHE.
• Outperformed conventional Co-N-C and Co-C3N4 systems in nitrate reduction.

Conclusions:

• CoPHI demonstrates superior performance for electrochemical nitrate-to-ammonia conversion.
• The material facilitates nitrate adsorption, water dissociation, and intermediate stabilization.
• CoPHI represents a significant advancement in sustainable ammonia synthesis and nitrate remediation.