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Graphene has been shown to act as an efficient sieve for hydrogen isotope separation since the perfect monolayer graphene is impermeable to almost all atoms and molecules but permeable to protons. Large-area graphene films can be produced by chemical vapor deposition (CVD) and exhibit a considerably high proton–deuteron separation factor of ∼8. However, the performance of the graphene-based membrane is often limited by the presence of cracks and imperfections introduced mainly during the transfer process. Here, we report a simple but effective method to transfer large-area CVD graphene onto commercial Nafion membranes with the aid of palladium thin films and thus fabricate the Pd/Graphene/Nafion composite membranes, which allow a proton–deuteron separation factor up to ∼10. This transfer method avoids the mechanical damage of graphene caused by deformation of the Nafion membrane. There is no need to remove the palladium thin film, and it will act as a catalyst for the reduction of hydrons during electrochemical pumping. The large-area transfer of graphene and fabrication of composite membranes for efficient separation of hydrogen isotopes will promote the development of graphene-based separation technologies. [ABSTRACT FROM AUTHOR]

Porous organic cages (POCs) are nanoporous materials composed of discrete molecular units that have uniformly distributed functional pores. The intrinsic porosity of these structures can be tuned accurately at the nanoscale by altering the size of the porous molecules, particularly to an optimal size of 3.6 Å, to harness the kinetic quantum sieving effect. Previous research on POCs for isotope separation has predominantly centered on differences in the quantities of adsorbed isotopes. However, nuclear quantum effects also contribute significantly to the dynamics of the sorption process, offering additional opportunities for separating H 2 and D 2 at practical operational temperatures. In this study, our investigations into H 2 and D 2 sorption on POC samples revealed a higher uptake of D 2 compared to that of H 2 under identical conditions. We employed quasi-elastic neutron scattering to study the diffusion processes of D 2 and H 2 in the POCs across various temperature and pressure ranges. Additionally, neutron Compton scattering was utilized to measure the values of the nuclear zero-point energy of individual isotopic species in D 2 and H 2. The results indicate that the diffusion coefficient of D 2 is approximately one-sixth that of H 2 in the POC due to the nuclear quantum effect. Furthermore, the results reveal that at 77 K, D 2 has longer residence times compared to H 2 when moving from pore to pore. Consequently, using the kinetic difference of H 2 and D 2 in a porous POC system enables hydrogen isotope separation using a temperature or pressure swing system at around liquid nitrogen temperatures.

Realizing ideal deuterium separation from isotopic mixtures remains a daunting challenge because of their almost identical sizes, shapes, and physicochemical properties. Using the quantum sieving effect in porous materials with suitable pore size and open metal sites (OMSs) enables efficient hydrogen isotope separation. Herein, synthetic HKUST-1-derived microporous mixed-valence Cu(I)Cu(II)-BTC (BTC = benzene-1,3,5-tricarboxylate), featuring a unique network of distinct Cu(I) and Cu(II) coordination sites, can remarkably boost the D 2 /H 2 isotope separation, which has a high selectivity ( S D 2 /H 2 ) of 37.9 at 30 K, in comparison with HKUST-1 and other porous materials. Density functional theory (DFT) calculations indicate that the introduction of Cu(I) macrocycles in the framework decreases the pore size and further leads to relatively enhanced interaction of H 2 /D 2 molecules on Cu(II) sites. The significantly enhanced selectivity of Cu(I)Cu(II)-BTC at 30 K can be mainly attributed to the synergistic effect of kinetic quantum sieving (KQS) and chemical affinity quantum sieving (CAQS). The results reveal that Cu(I) OMSs exhibit counterintuitive behaviors and play a crucial role in tuning quantum sieving without a complex structural design, which provides a deeper insight into quantum sieving mechanisms and a new strategy for the intelligent design of highly efficient isotope systems.

Single-layer graphene has been demonstrated to be a high-efficiency hydrogen isotope sieving membrane in the electrochemical hydrogen pumping system. In this work, we transferred this membrane to proton exchange membrane water electrolysis (PEMWE), which has wide industrial applications. Two membrane electrode assemblies with decorated Pt and ink-coated Pt were investigated. The graphene with the decorated Pt scheme acquired the reported highest proton-to-tritium separation factor of 19.50 in PEMWE. However, rather than graphene, the decorated catalyst was demonstrated to be responsible for this remarkable separation efficiency. Previous studies from Geim's group underestimated the enhanced separation efficiency of decorated Pt over ink-coated Pt, resulting in an exaggerated separation efficiency for graphene. The behavior of proton transfer with hydrogen isotope separation through graphene was interpreted by a serial-parallel circuit model, which suggested that hydrogen isotope separation occurs at defect sites. The limited separation efficiency for graphene was also well understood by a density functional theory (DFT) calculation using an SW 55-77 model and the transition state theory for the kinetic isotope effect. This research provides a thorough understanding of proton transfer with hydrogen isotope separation through graphene.