Working with the London Centre for Nanotechnology at University College London and the University of Oxford, scientists from Rutherford Appleton’s ISIS neutron source have developed a way of making microfibers just 1–3 µm in diameter, which form a tissue-like material that is safe to handle in air.
The new material contains as much hydrogen for a given weight as the high-pressure tanks currently used to store hydrogen, and can also be made in the form of microbeads that can be poured and pumped like a liquid.
Cella Energy has developed a method using a low-cost process called coaxial electrospinning or electrospraying. This traps a complex chemical hydride inside a nanoporous polymer, speeds up the kinetics of hydrogen desorption, reduces the temperature at which the desorption occurs, and filters out many if not all of the damaging chemicals. It also protects the hydrides from oxygen and water, making it possible to handle in air.
Cella Energy’s current composite material uses ammonia borane (NH3BH3) as the hydride, and polystyrene as the polymer nanoscaffold. Ammonia borane in its normal state releases 12 wt% of hydrogen between 110°C and 150°C, but with very slow kinetics.
In the Cella Energy approach the accessible hydrogen content is reduced to 6 wt%, but the temperature of operation is reduced, so that it starts releasing hydrogen below 80°C, and the kinetics are an order of magnitude faster. Cella is working to improve the hydrogen content while retaining the lower-temperature operation.
‘In some senses hydrogen is the perfect fuel; it has three times more energy than petrol per unit of weight, and when it burns it produces nothing but water,’ explains Professor Stephen Bennington, lead scientist on the project for the Science and Technology Facilities Council (STFC), which runs the Rutherford Appleton Laboratory.
‘But the only way to pack it into a vehicle is to use very high pressures or very low temperatures, both of which are expensive to do,’ continues Bennington. ‘Our new hydrogen storage materials offer real potential for running cars, planes and other vehicles that currently use hydrocarbons on hydrogen.’
‘Consumers want to be able to travel 300–400 miles before they have to refuel,’ adds Stephen Voller, CEO of Cella Energy Ltd. ‘And when they do have to fill up, they want to be able to do it as quickly as possible. Existing hydrogen storage methods do not meet these consumer expectations, but the ones we are developing have the potential to do just this.’
Cella Energy has just signed an agreement with specialty chemicals company Thomas Swan & Co Ltd, which will provide initial funding.