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

In the pursuit of sustainable ammonia synthesis and nitrate remediation, electrochemical nitrate reduction to ammonia (eNO₃RR) 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 eNO₃RR 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 μg 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 μg 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. H₂-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.