I saw the news last week but it took reading Dexter Johnson’s Dec. 2, 2014 post for me to achieve a greater understanding of why graphene’s proton permeability is such a big deal and of the tensions underlying graphene research in the UK.
Let’s start with the news, from a Nov. 26, 2014 news item on Nanowerk (Note: A link has been removed),
Published in the journal Nature (“Proton transport through one-atom-thick crystals”), the discovery could revolutionise fuel cells and other hydrogen-based technologies as they require a barrier that only allow protons – hydrogen atoms stripped off their electrons – to pass through.
In addition, graphene membranes could be used to sieve hydrogen gas out of the atmosphere, where it is present in minute quantities, creating the possibility of electric generators powered by air.
A Nov. 26, 2014 University of Manchester news release, which originated the news item, describes the research in greater detail,
One-atom thick material graphene, first isolated and explored in 2004 by a team at The University of Manchester, is renowned for its barrier properties, which has a number of uses in applications such as corrosion-proof coatings and impermeable packaging.
For example, it would take the lifetime of the universe for hydrogen, the smallest of all atoms, to pierce a graphene monolayer.
Now a group led by Sir Andre Geim tested whether protons are also repelled by graphene. They fully expected that protons would be blocked, as existing theory predicted as little proton permeation as for hydrogen.
Despite the pessimistic prognosis, the researchers found that protons pass through the ultra-thin crystals surprisingly easily, especially at elevated temperatures and if the films were covered with catalytic nanoparticles such as platinum.
The discovery makes monolayers of graphene, and its sister material boron nitride, attractive for possible uses as proton-conducting membranes, which are at the heart of modern fuel cell technology. Fuel cells use oxygen and hydrogen as a fuel and convert the input chemical energy directly into electricity. Without membranes that allow an exclusive flow of protons but prevent other species to pass through, this technology would not exist.
Despite being well-established, fuel-cell technology requires further improvements to make it more widely used. One of the major problems is a fuel crossover through the existing proton membranes, which reduces their efficiency and durability.
The University of Manchester research suggests that the use of graphene or monolayer boron nitride can allow the existing membranes to become thinner and more efficient, with less fuel crossover and poisoning. This can boost competitiveness of fuel cells.
The Manchester group also demonstrated that their one-atom-thick membranes can be used to extract hydrogen from a humid atmosphere. They hypothesise that such harvesting can be combined together with fuel cells to create a mobile electric generator that is fuelled simply by hydrogen present in air.
Marcelo Lozada-Hidalgo, a PhD student and corresponding author of this paper, said: “When you know how it should work, it is a very simple setup. You put a hydrogen-containing gas on one side, apply small electric current and collect pure hydrogen on the other side. This hydrogen can then be burned in a fuel cell.
“We worked with small membranes, and the achieved flow of hydrogen is of course tiny so far. But this is the initial stage of discovery, and the paper is to make experts aware of the existing prospects. To build up and test hydrogen harvesters will require much further effort.”
Dr Sheng Hu, a postdoctoral researcher and the first author in this work, added: “It looks extremely simple and equally promising. Because graphene can be produced these days in square metre sheets, we hope that it will find its way to commercial fuel cells sooner rather than later”.
The work is an international collaboration involving groups from China and the Netherlands who supported theoretical aspects of this research. Marcelo Lozada-Hidalgo is funded by a PhD studentship programme between the National Council of Science and Technology of Mexico and The University of Manchester.
Here’s more about the research and its implications from Dexter Johnson’s Dec. 2, 2014 post on the Nanoclast blog on the IEEE (Institute of Electronics and Electrical Engineers) website (Note: Links have been removed),
This latest development alters the understanding of one of the key properties of graphene: that it is impermeable to all gases and liquids. Even an atom as small as hydrogen would need billions of years for it to pass through the dense electronic cloud of graphene. In fact, it is this impermeability that has made it attractive for use in gas separation membranes.
But as Geim and his colleagues discovered, in research that was published in the journal Nature, monolayers of graphene and boron nitride are highly permeable to thermal protons under ambient conditions. So hydrogen atoms stripped of their electrons could pass right through the one-atom-thick materials.
The surprising discovery that protons could breach these materials means that that they could be used in proton-conducting membranes (also known as proton exchange membranes), which are central to the functioning of fuel cells. Fuel cells operate through chemical reactions involving hydrogen fuel and oxygen, with the result being electrical energy. The membranes used in the fuel cells are impermeable to oxygen and hydrogen but allow for the passage of protons.
Dexter goes into more detail about hydrogen fuel cells and why this discovery is so exciting. He also provides some insight into the UK’s graphene community (Note: A link has been removed),
While some have been frustrated that Geim has focused his attention on fundamental research rather than becoming more active in the commercialization of graphene, he may have just cracked open graphene’s greatest application possibility to date.
I recommend reading Dexter’s post if you want to learn more about fuel cell technology and the impact this discovery may have.
Richard Van Noorden’s Nov. 27, 2014 article for Nature provides another perspective on this work,
Fuel-cell experts say that the work is proof of principle, but are cautious about its immediate application. Factors such as to how grow a sufficiently clean, large graphene sheet, and its cost and lifetime, would have to be taken into account. “It may or may not be a better membrane for a fuel cell,” says Andrew Herring, a chemical engineer at the Colorado School of Mines in Golden.
Van Noorden also writes about another graphene discovery from last week, which won’t be featured here. Where graphene is concerned I have to draw a line or else this entire blog would be focused on that material alone.
Getting back back to permeability, graphene, and protons, here’s a link to and a citation for the research paper,
Proton transport through one-atom-thick crystals by S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R. R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, I. V. Grigorieva, H. A. Wu, & A. K. Geim. Nature (2014 doi:10.1038/nature14015 Published online 26 November 2014
This article is behind a paywall.