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70 hydrogen using formic acid (HCOOH). Although it is not a fuel, the use of formic acid to provide a source of hydrogen allows other, more volatile fuel sources such as gasoline to be discounted. When used at 85% concentration, formic acid is less dangerous than pure hydrogen, although there are still safety procedures to be followed. When heated, it produces carbon dioxide and water, and then, when exposed to catalysts, it decomposes into hydrogen and carbon monoxide. Formic acid is pumped from a cartridge using one of two metering diaphragm-driven pumps– one supplies the correct amount of formic acid for hydrogen production, the other supplies fuel through a heat exchanger to the catalytic burner to provide a continuous heat supply to the reformer. After exiting the heat exchanger, the reformate is mixed with a small amount of air and passed through a preferential oxidation reactor to bring the trace carbon monoxide content down to less than 10 ppm, which is a target of this development. The reformate is then passed to a fuel cell stack to produce electrical power, with anode off-gases being vented to the atmosphere; the air supply for the catalytic burner is provided by a small blower. The hydrogen produced by this process can then be used by a variety of fuel cell types – solid oxide fuel cells, proton exchange membrane and so on – for either grid-scale power or unmanned automotive power. The production of hydrogen in this way is a lot safer than traditional methods. Consequently the safety systems needed to protect the manufacturer can be reduced in line with the relative risk of production. For unmanned vehicles, the opportunities for local ‘reforming’ allow a measure of independence from any development in the national energy grids producing hydrogen. Despite the need for safety procedures in reforming hydrogen for unmanned use, the overall advantages in producing fuel this way are still more attractive than relying on battery power. Hydrogen pellet technology Hydrogen is not the easiest material to transport or use in a leak-free system to allow useful power to be extracted from it. To do so typically entails compressing it to 700 times atmospheric pressure or liquefying it at temperatures close to absolute zero for both transport and use. There is however a process that produces a solid hydrogen storage material that looks and feels like a plastic. It has a low toxicity and, although flammable, is no more dangerous than gasoline. The current developed process takes a material with a high useable hydrogen content by weight, and turns it into a hi-tech composite by combining it with a polymer. The resulting material then forms a microporous plastic-like solid that can be pressed, shaped or extruded into any form and to fit any space. The advantage with this is that Dec 2015/Jan 2016 | Unmanned Systems Technology Focus | Fuel cells Relative energy densities of fuel materials Power source Theoretical energy Theoretical energy density (Wh/kg) density (Wh/l) Lithium-ion 200 704 Lead-acid 30-40 60-75 Formic acid 1700 2086 Hydrogen (at 5000 psi) 33,333 833 Combining a hydrogen-containing material with a polymer yields a solid fuel – in this case in pellet form – that is safe to store and transport (Courtesy of Cella Energy) For unmanned vehicles, the opportunities for local ‘reforming’ allow a measure of independence from any national grids producing hydrogen