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

Abstract

In the pursuit of sustainable ammonia synthesis and nitrate remediation, electrochemical nitrate reduction to ammonia (eNO(3)RR) emerges as a promising alternative to the carbon-intensive Haber-Bosch process, which emits 1.6-2.0 tons of CO2 per ton of ammonia. Powered by renewable energy, the eNO(3)RR offers reduced emissions and energy consumption but faces challenges in catalytic activity and product selectivity due to its complex mechanism. To address these issues, CeFeO3 supported CeO2 composites were synthesized via a microwave polyol method with varying Ce:Fe atomic ratios and comprehensively characterized. Electrochemical analysis revealed that pure CeO2 achieved a high ammonia yield rate of 4040.5 +/- 262.5 mu g h(-1) cm(-2) but with a lower Faradaic efficiency (FE) of 52.8 +/- 2.8% at -0.45 V-RHE in 0.1 M KOH with 0.1 M NO3-. Introducing CeFeO3 into CeO2 enhanced FE significantly, reaching a maximum of 80.1 +/- 3.3% with an ammonia yield rate of 3223.9 +/- 168.3 mu g h(-1) cm(-2). Parasitic hydrogen evolution accounted for only 4.9 +/- 0.9% FE, while hydroxylamine and nitrite, key intermediates, contributed 8.3 +/- 1.2% and 6.7 +/- 0.9%, respectively. Stability was demonstrated over 25 one hour cycles (25 h total) at -0.45 V-RHE with electrolyte replacement. The intrinsic perovskite structure of CeFeO3, facilitating electron exchange via oxygen vacancies, underpinned the improved performance. H-2-NO3- fuel cell studies showed 74.6% thermodynamic efficiency at a current density of 29.7 mA cm(-2) at 0.46 V. This study underscores CeFeO3/CeO2 composites' potential for sustainable ammonia production and environmental remediation