Graphene: protons may pass

Materials World magazine
,
1 Jan 2015

Research led by Sir Andre Geim signals a breakthrough for hydrogen fuel cell technology. Simon Frost reports. 

It’s impermeable to atoms, but researchers at the University of Manchester have found that graphene allows protons to pass through it easily, especially at high temperatures – a potentially massive step forward for hydrogen fuel cell technology and separation applications. The research, published in Nature in November 2014, was headed by Sir Andre Geim, who shared the 2010 Nobel Prize in Physics for the isolation of single-atom-thick graphene six years before. The study also examined hexagonal boron nitride, finding that it, too, conducts protons far better than predicted.

PhD student Marcelo Lozada-Hidalgo explained that the proton exchange membrane in fuel cells ‘must allow protons to pass through the membrane, while preventing the fuel and contaminants to cross. But, as simple as it sounds, this is still one of the main challenges. To [prevent] fuel and contaminants from crossing over, the fuel cells have to be made very thick. But that, in turn, reduces the ease with which protons can cross, so makes it less efficient’.

In contrast, although only an atom thick, graphene cannot be penetrated by any atoms. It was believed that this would rule it out as a fuel cell membrane material, but this new quality could mean that the opposite is true. ‘Because graphene is impermeable to anything but protons we expect that [graphene] will allow for thinner and more efficient fuel cells,’ said Lozada-Hidalgo. Current state-of-the-art membranes do not completely prevent the mixing of fuel and oxidant, reducing efficiency. These kinds of membrane are formed of palladium and other precious metals, making them prohibitively expensive.

When asked about the potential of the findings, Geim admitted that, upon witnessing the unexpected result, ‘It was hard not to speculate,’ but stressed that this is only the first study in this area and theorists will need to take it further before any practical applications are realised. ‘Let me emphasise that futuristic is the word that has to be attributed to this particular research, because everything is shown only on a small size flake,’ he said. ‘But we can imagine that you can apply a small electric current through the membrane and push hydrogen through a graphene or boron nitrite membrane.’

However, not only could graphene prove the perfect fuel cell membrane, it could also be used to extract atmospheric hydrogen for use in electricity generation. Instead of burning fossil fuels in a combustion engine, clean fuel could be harvested from the air. ‘In the atmosphere, there is a certain amount of hydrogen, and this will end up on the other side [of the membrane] in a reservoir. You can use this collected hydrogen and burn it in the cell. Essentially, you pump the fuel from an atmosphere and get electricity out of it. In principle, before this paper, it wouldn’t even be speculation – it would be science fiction. The research provides guidance and proof that this kind of device is possible and doesn’t contradict any known laws of nature,’ claimed Geim.

Amazing properties of graphene:

Carries an electrical current 1,000 times denser than copper wire

200 times stronger than steel

At one atom thick, a stack of 3 million sheets would measure 1mm

Conducts heat 10 times better than copper