Electrochemical synthesis of useful chemicals such as ammonia through renewable electricity will ease problems associated with renewable energy storage. However, the strong NºN bond (941 kJ mol^-1) poses a severe challenge for mild condition synthesis of ammonia. Several attempts toward electrosynthesizing ammonia at low and high temperatures included a variety of electrode materials ranging from glassy carbon electrode to precious metals and different proton and oxide ion conducting electrolytes [1]. Rates on the order of 10^-9 mols^-1cm^-2 have been reported for both low and high temperature systems. While the formation of ammonia from H₂ and N₂ is exothermic, at low temperatures the reaction kinetics is too low for industrial production. The current high temperature Haber-Bosch process is too energy intensive and is not economically viable for small scale remote applications.

We report the synthesis of ammonia in a simple fuel cell configuration using a Sn₂P₂O₇ – nafion composite membrane and Pt electrodes in the low-intermediate temperature range of 200-300°C. The composite membrane showed conductivity values in the range of 10 – 20 mScm^-1 at 200°C. Our membranes retained high conductivity values after continuous operation over 300 hours. We observed an ammonia synthesis rate of 1.8x10^-9 mols^-1cm^-2 under a bias of -0.1 V with Pt based electrodes and H₂ and N₂ as reactant gases.

References

1. V. Kyriakou, I. Garagounis, e. Vasileiou, A. Vourros, and M. Stoukides, Catalysis Today, 2016 http://dx.doi.org/10.1016/j.cattod.2016.06.014.