Could fuel pellets pave way for hydrogen economy?
Hydrogen offers the promise of becoming an important fuel source in the future. With the prospect of zero emissions from motor vehicles, it could be a viable alternative to fossil fuels. However, it can be highly flammable which may lead to problems with storing and transporting it in vehicles. Researchers have now improved on a secure method of hydrogen storage which could overcome this problem.
Fuel cells work by combining hydrogen and oxygen to generate electricity, which powers a motor vehicle. The only emission is water, and hydrogen is therefore considered to be a clean fuel. As hydrogen is also potentially renewable and sustainable, there are considerable environmental benefits to using hydrogen to power motor transport. However, under normal conditions hydrogen is a highly flammable gas and must be kept either under high pressure or very low temperatures, complicating its use as a safe and portable fuel.
The researchers developed a new method of preparing an existing hydrogen storage medium so that it can be produced in higher quantities and purity. The material, ammonia borane (NH3BH3) powder, abbreviated as AB, safely releases hydrogen to power fuel cells. This development could bring widespread hydrogen fuel use a step closer. AB can be compressed into pellets and used in motor vehicles. When heated, it gives off hydrogen, which is consumed by the fuel cell. AB is more hydrogen-dense than liquid hydrogen: each millilitre of AB weighs about three-quarters of a gram and contains up to 1.8 litres of hydrogen gas. The pellets would take up less space than pressurised hydrogen fuel, which could allow vehicles to be manufactured that are similar in size and performance to current fossil-fuelled vehicles.
The newly developed production method produces high yields of AB powder. The method is efficient and simple and has the added advantage of producing the AB in a pure enough state to be potentially used as a stable form of on-board hydrogen storage. The researchers believe the process can be scaled-up to produce industrial amounts of the powder.
Scientists are conducting further research to control the rate of release of hydrogen from AB. It is envisaged that drivers could manipulate power from the fuel cells in much the same way that the accelerator pedal currently controls fuel in today's combustion engines. Methods to recycle the used fuel pellets are also being developed.
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