Large quantities of heavy water are used as a coolant in nuclear power plants. Generating heavy water is an energy-intensive task: producing just one kilogram of heavy water consumes enough energy to power an average American household for an entire year. Now, Graphene Flagship researchers have shown that using graphene filters could be a significantly more energy-efficient and scalable method of heavy water production.
Working within the Graphene Flagship, researchers at the University of Manchester demonstrated scalable prototypes of graphene membranes capable of producing heavy water. The new development could lead to the reduction of CO2 emissions associated with heavy water production by up to a million tonnes each year. The research, published in Nature Communications, suggests that just 30 m2 of graphene membrane could produce quantities of heavy water comparable to those of existing heavy-water productions plants.
Marcelo Lozada-Hidalgo, who led the research at the University of Manchester, said: "This is a crucial milestone in the path to taking this technology to industrial application. The potential gains are high enough to justify its introduction even in the highly conservative nuclear industry."
Graphene has been shown to be an effective filter for the separation of different isotopes of hydrogen. In heavy water, the hydrogen atoms in the water molecule are replaced by a heavier isotope of hydrogen called deuterium. The deuterium nucleus contains a proton and a neutron, in contrast to the single proton in a typical hydrogen nucleus. Natural water contains 0.015% deuterium, so extracting heavy water is typically an intensive multi-stage process.
To make the graphene filter membranes, the researchers transferred graphene grown by chemical vapour deposition onto flexible polymer films. To increase the rate of hydrogen transfer, they deposited palladium nanoparticles onto graphene surface to act as a catalyst. The graphene film is then sandwiched between conductive carbon cloth. Applying a potential across the membrane pumps the hydrogen through the graphene, separating it from deuterium.
The researchers estimate that the higher efficiency of the graphene filters could need one hundred times less energy than existing heavy water plants, making industrial production for nuclear power plants highly cost- and energy-effective. The prototype membranes could be scaled up to industrial quantities using roll-to-roll fabrication processes.
Tritium is another isotope of hydrogen, containing a proton and two neutrons. A by-product in nuclear reactors, it is radioactive and the graphene membranes are expected to be even more efficient for tritium separation and decontamination.
Sir Andre Geim of the University of Manchester, who received the 2010 Nobel prize in physics for experiments on graphene, added: "Tritium discharged both from nuclear power plants and as a result of environmental disasters is a major global concern. We believe this technology can economically transform the environmental footprint of future nuclear plants."
Andrea Ferrari of the University of Cambridge, UK, Science and Technology Officer and Chair of the Management panel of the Graphene Flagship added "Yet again graphene shows its potential in another key technological field, adding another promising direction on the roadmap for applications pursued by the Graphene Flagship."
M. Lozada-Hidalgo, S. Zhang, S. Hu, A. Esfandiar, I.V. Grigorieva, A.K. Geim, Nature Communications 8, 15215 (2017)