Ammonia is one of the most significant chemical products on the planet due to its central role in agriculture, as well as its use in a wide variety of chemical processes. More recently it has also attracted interest as a carbon-free energy vector, with an energy density similar to that of methanol and immediate compatibility with existing storage and distribution infrastructure. Current ammonia production relies on natural gas for both the hydrogen and the energy required by the high temperature, high pressure Haber-Bosch reaction. This technology consumes over 1% of all global energy and, in Europe, is responsible for 1% of all carbon emissions (1). New processes based on renewable power are therefore urgently required.

Electrochemical reduction of nitrogen to ammonia has been demonstrated in a number of systems, although very slow kinetics and competing reduction of protons to hydrogen has severely limited their efficiency, particularly in protic media (2). One promising approach operates in a molten LiCl-KCl eutectic, the unique electrolyte stabilising the unusual nitride anion and enabling direct reduction of nitrogen gas (3). It has been proposed that this ion can then react with hydrogen or even water at an anode to form ammonia in an electrochemically driven process. Despite promising initial rates and current efficiencies, there has been very little development of the proposed cell, particularly in terms of electrocatalyst composition and morphology.

Here we setup the proposed cell to investigate the feasibility of this approach. We use various methods to deposit metals (Ni, Co, Mo, Fe) onto carbon felt supports to produce a range of different gas electrodes. These electrodes are tested for ammonia synthesis from nitrogen and hydrogen and compared with the rates at a Ni foam electrode used in initial reports.

References

1. Proceedings of the International Fertiliser Society 2008, 639

2. V. Kyriakou, I. Garagounis, E. Vasileiou, A. Vourros, M. Stoukides, Catalysis Today 2017, 286, 2–13.

3. T. Murakami, T. Nishikiori, T. Nohira, Y. Ito, J. Am. Chem. Soc. 2003, 125 (2), 334–335.