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

摘要

Ammonia was directly synthesised from wet nitrogen at an intermediate temperature (375–425 °C) based on the oxygen-ion conduction of the Ce _(0.8) Gd _(0.18) Ca _(0.02) O _(2? δ ) –((Li/Na/K) _(2) CO _(3) ) composite electrolyte. A redox stable perovskite-based catalyst, La _(0.75) Sr _(0.25) Cr _(0.5) Fe _(0.5) O _(3? δ ) (LSCrF), was synthesised via a combined EDTA–citrate complexing sol–gel process to be used as a component of the La _(0.75) Sr _(0.25) Cr _(0.5) Fe _(0.5) O _(3? δ ) –Ce _(0.8) Gd _(0.18) Ca _(0.02) O _(2? 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 LaFeO _(3? δ ) , La _(0.6) Sr _(0.4) FeO _(3? 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 Cr ~(3+) ions at the B-site of doped LaFeO _(3) improves both the chemical stability and catalytic activity for ammonia synthesis.