Due to the combination of the worlds increasing energy demand and concerns of fossil-fuel combustion induced climate change, there is an imminent need to switch to carbon-free renewable energy sources such as solar. Solar irradiation is diurnal and intermittent, however, making it essential to store a large fraction of the converted energy. For these reasons photochemical water splitting to generate renewable hydrogen has attracted a lot of attention. Storage of the low-density gas is problematic, however, making the conversion to higher energy density fuels attractive. One option is the storage of renewable hydrogen as ammonia since it has a relatively high energy density, is carbon-free, and can potentially be decomposed back to nitrogen and hydrogen with the application of less than 0.1 V (compared to over 1.23 V for water electrolysis) or used in a direct ammonia fuel cell. In practice, however, large overpotentials are required to drive the overall ammonia electrolysis reactions resulting in poor energy conversion efficiencies. We have recently begun investigating reducing the ammonia electrolysis overpotentials through homogeneous and heterogeneous catalysis. Results of electrocatalytic ammonia splitting in organic solvents as well as in liquid ammonia at metal and metal oxide surfaces will be discussed. We found a striking dependence of the catalytic performance on the electrolyte composition in liquid ammonia. In addition, ammonia oxidation via a series of ruthenium poly-amine complexes will be presented.

Ammonia as the high-density solar fuel of the future

247th National Meeting (2014)

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