Synthesis of ammonia directly from wet nitrogen using a redox stable La0.75Sr0.25Cr0.5Fe0.5O3-δ-Ce0.8Gd0.18Ca0.02O2-δ composite cathode

Abstract

Ammonia was directly synthesised from wet nitrogen at an intermediate temperature (375-425°C) based on the oxygen-ion conduction of the Ce0.8Gd0.18Ca0.02O2-δ-((Li/Na/K)2CO3) composite electrolyte. A redox stable perovskite-based catalyst, La0.75Sr0.25Cr0.5Fe0.5O3-δ (LSCrF), was synthesised via a combined EDTA-citrate complexing sol-gel process to be used as a component of the La0.75Sr0.25Cr0.5Fe0.5O3-δ-Ce0.8Gd0.18Ca0.02O2-δ composite cathode for ammonia synthesis. Ammonia formation was studied at 375, 400 and 425°C and a maximum ammonia formation rate of 4.0 × 10-10 mol s-1 cm-2 with corresponding Faradaic efficiency of 3.87% was observed at 375°C when the applied voltage was 1.4 V. This is much higher than 7.0 × 10-11 mol s-1 cm-2 at 1.4 V and 400°C when Cr-free Sr-doped LaFeO3-δ, La0.6Sr0.4FeO3-δ was used as the catalyst for the electrochemical synthesis of ammonia, indicating LSCrF is potentially a better catalyst. Ammonia was successfully synthesised using a redox stable cathode with higher formation rates at reduced temperature. Introduction of Cr3+ ions at the B-site of doped LaFeO3 improves both the chemical stability and catalytic activity for ammonia synthesis.