The Fabrication Of Graphene/Nafion Composite Membranes And Their Application For Hydrogen Isotope Separation

Graphene has been shown to act as an efficient sieve for hydrogen isotope separation since perfect monolayer graphene is impermeable to almost all atoms and molecules but highly permeable to hydrons(H~+/D~+/T~+).Chemical-vapor-deposited(CVD)graphene can be produced in large scale and exhibit a considerably high hydrogen isotope separation ability.In order to achieve efficient separation of hydrogen isotopes,it is necessary for CVD graphene to be transferred from the growth substrate to the target substrate,while ensuring the intactness.This puts forward higher requirements for graphene transfer,and requires improvement or development of new transfer methods to obtain large-area high-quality graphene intactly and achieve excellent separation ability of hydrogen isotopes.Here,using large-scale CVD graphene and commercial Nafion membranes as starting materials,a new fabrication method and Graphene/Nafion composite membranes with novel structure have been developed.High-quality graphene-based composite membranes were prepared successfully to achieve efficient separation of hydrogen isotopes.(1)A Graphene/Nafion composite membrane with double-stage structure was fabricated.Compared with the single-stage Graphene/Nafion composite membrane,the double-stage Graphene/Nafion composite membranes reduce the impact of graphene breakage on hydrogen isotope separation and improve the overall coverage of graphene.The morphology and resistance of the composite membranes indicate that they have high integrity and uniformity.Hydrogen isotope separation test finds that the double-stage Graphene/Nafion composite membranes exhibit excellent separation ability of hydrogen isotopes,with a separation factor up to 9.2 and an average value of～7.5,better than that of single-stage Graphene/Nafion composite membranes(the highest separation factor of 8.4and an average value of～6.8).(2)A method of transferring CVD graphene onto the Nafion membrane with the aid of Pd thin film has been developed,which avoids the contact between Nafion membrane and etching solution,mitigates the deformation of Nafion membrane,eliminates the damage caused by the deformation of Nafion membrane.High-quality Pd/Graphene/Nafion composite membranes has been fabricated.The morphology of surface and elemental imaging analysis shows that graphene is transferred successfully to the Nafion membrane with high integrity and uniformity.The Pd thin film not only plays a role in assisting the transfer of graphene but also can be directly integrated into the device as a catalyst for the reduction of H~+and D~+that are electrochemically generated and transport through the membrane.The test of hydrogen isotope separation finds that the Pd/Graphene/Nafion composite membrane has excellent separation ability of hydrogen isotopes,with a separation factor up to 9.7 and an average value of～8.1.The method of fabricating graphene-based composite membranes proposed in this paper can be used to improve the hydrogen isotope separation ability of graphene-based composite membranes,which is expected to promote the development of graphene separation technology.