Electrochemical Synthesis of Ammonia with Proton Conducting Solid Electrolyte Fuel Cells at Intermediate Temperatures

Electrochemical synthesis of ammonia with solid electrolyte fuel cells using proton conducting solid electrolyte such as barium cerate was investigated at intermediate temperature of around 773 K. Electrode catalysts of metal alloys and mixed conductors including metals of Pd and Ru as active sites were synthesized. Two-electrode configuration was employed with dynamic hydrogen electrode (DHE) for CE, i.e., WE(N₂)|solid electrolyte|CE(H₂). It was observed that ammonia formed on the working electrode (WE) through the reaction of nitrogen with proton diffusing from the counter electrode (CE). The production rate of ammonia was influenced by electrode potential and it showed the maximum at around -300~-500 mV for both of Pd and Ru-based electrodes. Ru-based catalyst that might promote nitrogen bond dissociation showed good performance on ammonia formation. The electrode optimization was also discussed in terms of conduction paths of proton and electron in the electrodes.