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Novel Electrochemical Exfoliation Approach to the Synthesis of Large Area, Defect-Free and Single Layer Graphene and Its Application in Fuel Cells

Periodic Reporting for period 1 - GRAPHENERGY3 (Novel Electrochemical Exfoliation Approach to the Synthesis of Large Area, Defect-Free and Single Layer Graphene and Its Application in Fuel Cells)

Reporting period: 2015-08-17 to 2017-08-16

Separating hydrogen isotopes is a task of vast proportions. Over a thousand tons of heavy water (D2O) are produced every year to supply nuclear reactors worldwide as well as for medical and research applications. The production remains expensive for two reasons. First, the low natural abundance of deuterium (0.015%) implies that huge amounts of water should be processed (the industry standard for initial enrichment is 20% of D2O). Second, current technologies often need hundreds of stages to achieve the required degree of separation. This means that heavy-water plants are large even compared to many chemical plants. These issues result in high capital costs and large energy consumption. Indeed, producing 1 kg of enriched heavy water requires about 10 MWh , the annual energy consumption of a typical US household. Separating tritium—hydrogen’s heaviest isotope—is equally important and challenging, not least for its radioactivity. Nuclear reactors produce tritium during their operation, which has to be continuously removed to ensure optimum performance. Furthermore, experimental fusion facilities require tritium as a fuel, whereas accidents like the one at Fukushima Daiichi leave behind thousands of tons of diluted tritiated water. The current demand stimulates search for new separation technologies that could provide higher separation factors, reduce the number of stages and minimize the energy consumption.

It has recently been shown that perfect monolayers of graphene – impermeable to thermal atoms and molecules – are permeable to hydrogen nuclei. Moreover, the two-dimensional (2D) crystals could efficiently separate protons from deuterons. However, those studies used micron-size crystals obtained by exfoliation, a method unsuitable for industrial-scale applications. So the aim of this project is to explore the feasibility of graphene-based electrochemical pumps for industrial-scale separation of hydrogen isotopes.
(1) A roll-to-roll technique has been developed to fabricate large area CVD graphene membrane with the coverage of ~95% on Nafion. The fabrication can be extended to produce graphene-on-Nafion membranes of virtually any size, following recent advances in growth and transfer of large area CVD graphene.

(2) A high proton-deuteron separation factor of ~8 has been achieved using our graphene based electrochemical pumps. For example, for equal amounts of protium and deuterium in the feed (50% H atomic fraction), protium accounts for up to ≈90% of atoms in the permeate.

(3) The energy consumption is projected to be orders of magnitude smaller with respect to existing technologies. A membrane based on 30 square meter of graphene, a readily accessible amount, could provide a heavy-water output comparable to that of modern plants.

(4) The new technology will be even more attractive for tritium decontamination and extraction. The identified mechanism behind proton-deuteron sieving implies a separation factor of ~30 for protium-tritium separation.

The research results above have been reported in journal Nature Communications. The dissemination of the work has been undertaken through presentations at National graphene institute, Manchester and at 2017 Graphene week held in Athens, Greece.
Graphene-based membranes could make the production of heavy water more efficient through its ability to effectively isotopically separate particles, leading to greener and cheaper nuclear power.
This is a crucial milestone in the path to taking this revolutionary technology from our lab to the industry. This technology can economically transform the environmental footprint of future nuclear plants.
The work has been widely publicised through various media including Phy.org.
hydrogen isotope separation membranes