Tunneling effects in the kinetics of helium and hydrogen isotopes desorption from single-walled carbon nanotube bundles

Abstract

The kinetics of desorption both helium isotopes and molecules of hydrogen and deuterium from open-ended or γ-irradiated single-walled carbon nanotube bundles was investigated in temperature range of 10–300 K. The gases desorption rates obey the Arrhenius law at high temperatures, deviate from it with temperature reduction and become constant at low temperatures. These results indicate the quantum nature of gas outflow from carbon nanotube bundles. We had deduced the crossover temperature below which the quantum corrections to the effective activation energy of desorption become significant. This temperature follows linear dependence against the inverse mass of gas molecule and is consistent with theoretical prediction.

Flow-Induced Autonomic Ordering of Hydrogen Molecules under a Non-Equilibrium Flow

“…The mean-square displacements (MSDs) including the dynamics along the z -axis become smaller as the CNT radius is smaller, as the temperature is lower, and as the density is higher (Figure S11). The equilibrium MSD in T L – S – n h is extremely small, being in harmony with the extremely slow diffusion of hydrogen molecules previously found inside a CNT in an equilibrium state at cryogenic temperature, − although our density is lower than theirs (Table S1). In contrast, the non-equilibrium flows let all of the MSDs nonlinearly grow regardless of the CNT radii and the thermodynamic conditions.…”

“…Hydrogen molecules possessing strong nuclear quantumness such as nuclear delocalization and zero-point energy exhibit peculiar properties inside a CNT in comparison with the classical molecules mentioned above due to the enhanced confinement, which has been actually observed and evidenced as the anomalous diffusion dynamics and structure of hydrogen molecules inside CNTs in equilibrium states. − The nuclear quantumness should also play a critical role in correctly describing a non-equilibrium flow of condensed hydrogen molecules inside a CNT where temperature and density rapidly change in a single-nanometer range. In spite of its importance for transfer and storage of hydrogen molecules as a renewable energy source, − it has been theoretically challenging to simulate such a non-equilibrium flow of hydrogen molecules because most path integral methods for treating the strong nuclear quantumness are based on an equilibrium partition function that requires uniform temperature and density in an equilibrium state …”

The effect of the thermal reduction on the kinetics of low-temperature 4He sorption and the structural characteristics of graphene oxide

“…The nonmonotonic behavior of the temperature dependences of the characteristic times of the 4 He sorption by the GtO and TRGO-200 samples is most likely accounted for by a competition between thermally activated diffusion dominant at T>12 K and the tunneling process prevailing at temperatures. Similar effects were also observed while investigating the gas sorption by fullerite C 60 , single-walled carbon nanotubes [21,22] and chemically reduced graphene [20]. The tendency for a growth of the characteristic times of 4 He sorption with the thermal treatment temperature observed for the TFGO-200 and TRGO-300 samples, as against the starting GtO (Fig.…”

“…Tunnel diffusion of light impurities at low temperatures was also observed in other carbon nanostructures, specifically in carbon nanotubes [21,22] and fullerite C 60 [23][24][25]. This led us to assume that the kinetics of gas sorption by carbon nanostructures was significantly influenced by the potential relief of their surfaces.…”

Nuclear Quantum Effects in the Layering and Diffusion of Hydrogen Isotopes in Carbon Nanotubes

“…Steric hindrance in narrow carbon nanopores caused by the higher excluded volume of H 2 was used to explain its slower self-diffusion (i.e., the Chudley–Elliott jump-diffusion mechanism), whereas D 2 was found to exhibit liquid-like self-diffusion . Similarly, the impact of nuclear quantum effects on diffusion of gases from single-carbon nanotubes has been studied experimentally, , revealing that H 2 diffuses out of the interior of carbon nanotubes at significantly faster rates than D 2 . Taken together, these works illustrate the importance of nuclear quantum effects in nanoconfined environments and motivates a more complete analysis of the range of phenomenology that may be observed in nanoconfined mixtures of H 2 and D 2 .…”