Ammonia synthesis by the Haber-Bosch (HB) process paved the way for rapid increase in crop production and sustained the needs of population growth. However, HB process is cost and energy intensive and releases about 260 million tons of CO₂ every year. Considering the threat associated with CO₂, finding an alternative, cheap and environmentally benign methodology for ammonia synthesis is highly desirable. Electrochemical synthesis through renewable electricity offers a viable alternative, although the synthesis rates reported are far from adequate. This is mainly due to the strong NºN bond (941 kJ mol^-1) that 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. This rate is still three orders of magnitude lower than the required rates for commercialization.

We have achieved ammonia synthesis rates of 1x10^-8 mols^-1cm^-2 at 200 °C in a simple fuel cell configuration using a Sn₂P₂O₇ – nafion composite membrane and Pt based catalyst [2]. Here we will present our results obtained with alternate electrocatalysts and discuss the role of applied potential and back pressure measurements on the synthesis rates of ammonia.

References

1. V. Kyriakou, I. Garagounis, e. Vasileiou, A. Vourros, and M. Stoukides, Catalysis Today, 2017, 286, 2-13.
2. K. P. Ramaiyan, S. Maurya, Y. S. Kim, F. H. Garzon, R. Mukundan, C. R. Kreller, Meeting Abstracts, ECS 231^st meeting. Issue 31, 1464-1464.

Acknowledgements

This project is supported by ARPA-E under Award No. DE-AR0000687.