Hydrogen storage at room temperature for fuel cells

Materials World magazine
,
1 Feb 2008
Hydrogen molecules (red) surround an ethylene molecule (green) that is attached to two titanium atoms (blue)

Scientists at the University of Virginia, based in Charlottesville, USA, claim to have discovered a material that can store large quantities of hydrogen at room temperature. This could help in the search for a more efficient and affordable hydrogen-powered fuel cell.

Drs Bellave Shivaram and Adam Phillips have created a 2.5nm thin film that can absorb up to 14% hydrogen by weight at room temperature. Previous materials have only been able to store seven to eight per cent, they say. The researchers are working from a theory proposed at the National Institute of Standards and Technology, USA, in 2006, that transition metal atoms attached to ethylene could bind large numbers of hydrogen molecules.

The novel storage structure consists of titanium atoms complexed with ethylene and laser deposited onto a silicon oxide substrate. Titanium has been shown to bind hydrogen molecules through electron donation, ‘but if the titanium atoms are not isolated, they will cluster together and reduce the number of hydrogen atoms that can bind’, explains Phillips. ‘We believe the ethylene acts to isolate the titanium atoms.’

Shivaram adds, ‘We have now measured the partial pressure of these molecules and have direct evidence that they are collecting on the sensor (silicon oxide). [Once] collected in the centre, we expose [the molecules] to hydrogen’.

While the researchers are excited about the possibilities of this material for viable fuel cells, they say it is too early to make predictions about its future. ‘We still need to make a big step, which is to show that the hydrogen can come out [of the material]. We haven’t done that yet because of limitations in our apparatus,’ says Shivaram.

John Kilner, Professor of Energy Materials at Imperial College London, UK, agrees that the thin film shows potential for high-impact applications, ‘but they’ve only done it on a small piece of material. The questions are – how scaleable is it? How recyclable is it? They may have achieved 14% once, but can they do it hundreds of times [with the same substrate], which is what you’d require for a practical material?’

Phillips notes, ‘At this point we are trying to determine exactly what our material is [using spectroscopic analysis]. Once we know that, we can try other deposition techniques and compare the materials’ structures’.

 

Further information:

University of Virginia Physics Department