A recently discovered form of carbon graphite has a completely unexpected property that scientists say could revolutionize the development of renewable energy and electric cars.
According to results published in the journal Nature, researchers at the University of Manchester have discovered that graphene — a one-atom-thick layer of graphite — allows positively charged hydrogen atoms (protons) to pass through it, despite being completely impermeable to all other gases. This could have amazing implications for the efficiency of fuel cells and other hydrogen-based technologies as they require a barrier that only allows protons to pass through.
First isolated and explored in 2004 by a team at The University of Manchester, graphene is renowned for its barrier properties, which is used in a number of applications such as corrosion-proof coatings and impermeable packaging.
Recently, a group of researchers led by Sir Andre Geim found that, despite expectations to the contrary, protons pass through graphene’s ultra-thin crystals rather easily, especially at elevated temperatures and if the films are 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.
“In the atmosphere there is a certain amount of hydrogen and this hydrogen will end up on the other side [of graphene] in a reservoir,” said Geim. “Then you can use this hydrogen-collected reservoir to burn it in the same fuel cell and make electricity.”
Despite its growing popularity as a power source for everything from cars to data centers, fuel-cell technology requires further improvements to make it more widely used. As the researchers explain, 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, which can boost competitiveness of fuel cells.
The Manchester team also demonstrated that their one-atom-thick membranes can be used to extract hydrogen from a humid atmosphere. They hypothesize 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 co-author of the 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 co-author of the paper, added: “It looks extremely simple and equally promising. Because graphene can be produced these days in square meter sheets, we hope that it will find its way to commercial fuel cells sooner rather than later.”