Invention could solve 'bottleneck' in developing pollution-free cars
Date: Monday, December 04, 2006 @ 21:58:02 UTC
Topic: Science
Hydrogen-powered cars that do not pollute the environment are
a step closer thanks to a new discovery which promises to solve the
main problem holding back the technology. Whilst hydrogen is thought to
be an ideal fuel for vehicles, producing only water on combustion, its
widespread use has been limited by the lack of a safe, efficient system
for onboard storage.
Scientists have experimented with ways of storing
hydrogen by locking the gas into metal lattices, but metal hydrides
only work at temperatures above 300°C and metal organic framework
materials only work at liquid nitrogen temperatures (-198°C).
Now scientists at the University of Bath have invented a material
which stores and releases hydrogen at room temperature, at the flick of
a switch, and promises to help make hydrogen power a viable clean
technology for the future.
Although its fuel to weight ratio is insufficient to make an entire
hydrogen tank from it, the material could be used in combination with
metal hydride sources to store and release energy instantaneously
whilst the main tank reaches sufficient temperature, 300°C, to work.
They hope to have the fully-working prototype ready within two to three years.
"The problem of how to store hydrogen has been a major bottleneck
in the development of the hydrogen power technology," said Dr Andrew
Weller from the Department of Chemistry at the University of Bath (UK).
"Hydrogen has a low density and it only condenses into liquid form
at -252°C so it is difficult to use conventional storage systems such
as high-pressure gas containers which would need steel walls at least
three inches thick, making them too heavy and too large for cars.
"The US Department of the Energy has said that it wants six per
cent of the weight of hydrogen storage systems to be hydrogen in order
to give new hydrogen powered cars the same kind of mileage per tank of
fuel as petrol-based systems.
"Whilst metal hydrides and metal organic framework materials can
achieve this kind of ratio, they only work at extremes of temperature
which are difficult to engineer into an ordinary vehicle.
"Our new material works at room temperature and at atmospheric
pressure at the flick of a switch. Because it is made from a heavy
metal (Rhodium), its weight to fuel ratio is low, 0.1 per cent, but it
could certainly fill the time lag between a driver putting their foot
on the accelerator and a metal hydride fuel tank getting up to
temperature.
"We are really very excited about the potential this technology offers."
The University of Bath researchers made the discovery whilst
investigating the effect that hydrogen has on metals. Having
constructed an organo-metallic compound containing six rhodium (a type
of metal that is also currently found in catalytic converters in cars)
atoms and 12 hydrogen atoms, they began studying the chemical
properties of the complex with researchers in Oxford (UK) and Victoria
(Canada).
They soon realised that the material would absorb
two molecules of hydrogen at room temperature and atmospheric pressure
– and would release the molecules when a small electric current was
applied to the material.
This kind of take up and release at the atomic scale makes the
material an ideal candidate for solving the hydrogen storage problem.
The researchers are now looking at ways of printing the material
onto sheets that could be stacked together and encased to form a
storage tank.
Potentially this tank could sit alongside a metal hydride tank and
would kick into action as soon as the driver put their foot on the
accelerator, giving the metal hydride store the time to heat up to
300°C - the temperature that normal petrol-powered engines run at.
"With the growing concern over climate change and our over-reliance
on fossil fuels, hydrogen provides us with a useful alternative," said
Dr Weller.
"We have been able to use hydrogen to power fuel cells, which
combine hydrogen and oxygen to form electricity and energy, for a
number of years.
"But whenever the fuel is considered for cars we hit the stumbling block of how to store hydrogen gas in everyday applications.
"The new material absorbs the hydrogen into its structure and
literally bristles with molecules of the gas. At the flick of a switch
it rejects the hydrogen, allowing us to turn the supply of the gas on
and off as we wish.
"The fact that we discovered the material by chance is a fantastic advertisement for the benefits of curiosity driven research.
"In principle it should be possible to produce ready amounts of
hydrogen using sea water and solar cells, giving the next generation of
vehicles an inexhaustible supply of environmentally-friendly fuel.
"In fact other research in Bath’s Department of Chemistry is at the
forefront of the solar cell research, new battery technologies and new
fuel cell technologies which could help unlock what many people are
calling the hydrogen economy.
Source: University of Bath
Article from: http://www.physorg.com/news84450917.html
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