Sieving hydrogen isotopes through two-dimensional crystals

Abstract

One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to separate hydrogen ion isotopes. Using electrical measurements and mass spectrometry, we found that deuterons permeate through these crystals much slower than protons, resulting in a separation factor of ≈10 at room temperature. The isotope effect is attributed to a difference of ≈60 milli-electron volts between zero-point energies of incident protons and deuterons, which translates into the equivalent difference in the activation barriers posed by two-dimensional crystals. In addition to providing insight into the proton transport mechanism, the demonstrated approach offers a competitive and scalable way for hydrogen isotope enrichment.

Veritable electronic characteristics in ZnO nanowire circuits uncovered by the four-terminal method at a low temperature

“…For example, the electronic characteristics of the contact strongly depend on the metal work function and electron affinity. 10,11 Therefore, a deep understanding electronic characteristics of the advanced circuits that involves these semiconductor channels, including the nature of carrier transport in channels and the electrical properties of the metal-semiconductor contact interfaces, is an essential subject of intense scientific and engineering interest for their practical applications. 12,13 However, it is still a great challenge to make a distinction between channel resistance and contact resistance for these two-terminal devices.…”

Giant photo-effect in proton transport through graphene

“…Further measurements involving hydrogen's isotope deuterium have shown that this barrier is in fact 0.2 eV higher than the measured activation energy because the initial state of incoming protons is lifted by zero-point oscillations at oxygen bonds within the proton-conducting media used in the experiments 2 . The resulting value of 1.0 eV for the graphene barrier is somewhat lower (by at least 30%) than the values obtained theoretically for ideal graphene 1,[8][9][10][11] , which triggered a debate about the exact microscopic mechanism behind the proton permeation [8][9][10][11][12][13] .…”

“…On the opposite side, a protonconducting polymer (Nafion 14 ) was drop cast and then contacted with a proton-containing PdH x electrode 1 . In this setup, if a negative bias is applied to graphene, protons are injected from PdH x into the Nafion film and then pass through the graphene membrane, evolving into H 2 on the side decorated with Pt nanopartciles 1,2 . Graphene -a mixed electron-proton conductor -acts here as both proton conducting membrane and cathode.…”

“…The devices used in this work were made from monocrystalline graphene obtained by mechanical exfoliation. The graphene crystals were suspended over microfabricated holes (10 m diameter) etched in silicon-nitride films, following the recipe reported previously 1,2 . The resulting free standing membranes were decorated on one side with Pt nanoparticles deposited using electron-beam evaporation (Fig.…”

“…The latter observation also remains to be fully understood. Independently of fundamentals of the involved mechanisms, the high proton conductivity of graphene membranes combined with their impermeability to other atoms and molecules entices their use for various applications including fuel cell technologies and hydrogen isotope separation [1][2][3][4] . For example, it was argued that mass-produced membranes based on chemicalvapor-deposited graphene can dramatically increase efficiency and decrease the costs of heavy water production 4 .…”