Electrochemical Nitrogen Fixation Using CeFeO₃ and CeO₂ for Ammonia Synthesis and Nitrate Remediation

Area of Science:

• Electrochemistry
• Materials Science
• Environmental Science

Background:

• The Haber-Bosch process for ammonia synthesis is energy-intensive and contributes significantly to CO2 emissions.
• Electrochemical nitrate reduction to ammonia (eNO3RR) presents a sustainable alternative, powered by renewable energy, but faces challenges in catalytic activity and selectivity.
• Nitrate remediation is crucial for environmental protection, and efficient conversion methods are needed.

Purpose of the Study:

• To synthesize and characterize CeFeO3 supported CeO2 composites for enhanced eNO3RR.
• To evaluate the catalytic performance, selectivity, and stability of these composites for ammonia production and nitrate remediation.
• To investigate the potential of these materials in a H2-NO3- fuel cell system.

Main Methods:

• CeFeO3 supported CeO2 composites were synthesized using a microwave polyol method with varying Ce:Fe atomic ratios.
• Electrochemical performance was assessed using techniques like cyclic voltammetry and chronoamperometry.
• Product analysis was performed to determine ammonia yield, Faradaic efficiency (FE), and identify intermediates like hydroxylamine and nitrite.

Main Results:

• Pure CeO2 achieved an ammonia yield rate of 4040.5 ± 262.5 μg h-1 cm-2 with 52.8 ± 2.8% FE.
• CeFeO3/CeO2 composites significantly improved FE to a maximum of 80.1 ± 3.3% while maintaining a high ammonia yield rate of 3223.9 ± 168.3 μg h-1 cm-2.
• Parasitic hydrogen evolution was minimal (4.9 ± 0.9% FE), and the composites demonstrated stability over 25 hours of operation.

Conclusions:

• CeFeO3/CeO2 composites exhibit superior performance for eNO3RR compared to pure CeO2, attributed to the perovskite structure facilitating electron exchange via oxygen vacancies.
• These materials show great promise for sustainable ammonia synthesis and effective nitrate remediation.
• The study highlights the potential of CeFeO3/CeO2 composites in H2-NO3- fuel cells, achieving 74.6% thermodynamic efficiency.