While ammonia has a narrow flammability range and its toxicity is a concern, its strong smell is, however, useful for identifying leaks. However, each of these conversions carries an energy penalty. Alternatively, ammonia can be combusted directly or used in an ammonia-įed fuel cell. Hydrogen can be released on demand from ammonia through catalytic decomposition and consumed in a proton exchange membrane (PEM) fuel cell 3. The ubiquitous abundance of nitrogen in the air – as opposed to carbon - supports the use of a carbon-free hydrogen carrier for a future, large-scale and sustainable energy storage cycle 2.Īmmonia is a promising hydrogen carrier owing to its high hydrogen content (17.65 wt%), established distribution network and ability to be liquefied at 10 bar or -33☌. In these projects, ammonia is produced by combining hydrogen from water splitting with nitrogen from the air. In contrast to other forms of chemical storage, ammonia is the only carbon-free hydrogen carrier and can be synthesised from renewable sources as demonstrated by the opening of a pilot plant by Siemens in Oxfordshire, UK in June 2018 and a “green ammonia” plant by Nel Hydrogen and Yara starting up in Western Australia this year. Compared to conventional fuels, hydrogen has a low volumetric energy density in both gas and liquid form. Gaseous hydrogen storage requires high pressure vessels of up to 70 MPa while liquid storage needs cryogenic tanks maintained at -253☌. Hydrogen-enriched compounds which are liquid at mild conditions, such as ammonia, methane and methanol, have recently gained attention as a distribution medium or for storage of hydrogen. Ammonia is explored as a complementary future energy vector with applications in specific cases. In this article, we focus on the chemical storage of hydrogen in the form of ammonia to alleviate hydrogen’s storage and safety issues. This challenge has driven extensive research into battery, capacitor and chemical energy storage as buffer systems to balance the variation of renewable energy supply on the grid.Īs detailed in a previous article of this series 1, a significant obstacle to the wider implementation of hydrogen in energy trade is its costly and energy-intensive storage coupled with safety concerns associated with its high flammability. The intermittency and seasonal variation of solar and wind power leads to a mismatch between energy supply and demand, which will intensify as we decrease our dependence on traditional gas and coal-powered generators. TRANSITIONING our energy economy away from fossil fuel dependence towards one based on renewable and alternative forms of energy requires novel solutions for energy storage, in which the role of hydrogen has promising potential.
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