Electrochemical synthesis of ammonia based on a carbonate-oxide composite electrolyte

Electrochemical synthesis of ammonia based on carbonate electrolyte is presented in this paper. Spinel oxide CoFe2O4 was synthesised via a co-precipitation method and characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ammonia was successfully synthesised from hydrogen and nitrogen under atmospheric pressure using CoFe2O4 as catalyst (primary particle size 10–20 nm) together with silver at the cathode, Ag–Pd at the anode and carbonate-LiAlO2 composite as electrolyte respectively. Ammonia formation was observed at 400, 425 and 450 °C and the maximum rate of ammonia production was found to be 2.32 × 10−10 mol s−1 cm−2 at 400 °C and 0.8 V. The AC impedance measurements were recorded before and after the ammonia synthesis at 400, 425 and 450 °C. The electrolytic cell during the ammonia synthesis process was more stable at 450 °C and 0.8 V over a period of 2 h. This experiment also indicates that the carbonate-LiAlO2 composite electrolyte exhibits proton conduction.

Research Highlights
► Electrochemical synthesis of ammonia based on carbonate electrolyte.
► Proton conduction in carbonate-LiAlO2 composite demonstrated.
► The carbonate-LiAlO2 composite is stable at 450 °C.
► CoFe2O4 is active for ammonia synthesis.