Electrochemical synthesis of ammonia directly from air and water using a Li+/H+/NH 4+ mixed conducting electrolyte

Ammonia has been successfully synthesised directly from air and water using an electrochemical cell based on an H+/Li+/NH4+ mixed conducting membrane and Pt/C electrodes. It is found that the Nafion 211 membrane exhibits mixed H+/Li+ conduction after exchanging in 0.1 M Li2SO4 solution. The ionic conductivity of the mixed conductor is slightly lower than that of H+-form Nafion 211. The introduction of Li+ ions to the cell did not improve the ammonia formation rates in our experiments. Reasonably higher temperature may favour ammonia formation and the highest ammonia formation rate (9.37 × 10−6 mol m−2 s−1) and Faraday efficiency (0.83%) was obtained at 80 °C when a voltage of 1.2 V was applied. The ammonia formation rate decreased when 0.1 M Li2SO4 solution instead of water was used in the cell. Under the applied potential, the presence of Li+ ions might have a blocking effect on the transfer of protons resulting in a lower current at higher applied voltage, particularly at lower temperatures.