Abstract
We report results of vibrational neutron spectroscopy investigation aimed to identify the state of hydrogen adsorbed in ultramicroporous carbon. The mobility of hydrogen confined in carbon pores was probed as a function of temperature and pressure using inelastic neutron scattering, and the molecular translational and rotational motions were studied. At low loading rotation of H2 molecules adsorbed in the smallest carbon pores (∼4–5 Å) is severely hindered, suggesting that the interaction between H2 and the host matrix is anisotropic. At higher loading, H2 molecules behave as a nearly free rotor, implying lower anisotropic interactions with adsorption sites. At 77 K where bulk H2 is a gas, deconvolution of elastic/quasielastic signal provide evidence of pressure-dependent fractions of immobile (solid-like) and partially mobile (liquid-like) hydrogen, which correlate with the excess adsorption isotherm at 77 K. Effective H2 density in pores changes from solid-like to liquid-like with increasing pressure at 77 K. Surprisingly, immobile and partially mobile H2 is present even at temperatures as high as ∼110 K where bulk hydrogen exists only in gas form.
Original language | English |
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Pages (from-to) | 383-392 |
Number of pages | 10 |
Journal | Carbon |
Volume | 117 |
DOIs | |
State | Published - Jun 1 2017 |
Funding
The research at ORNL's Spallation Neutron Source was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy. This research was supported in part by the ORNL Postdoctoral Research Associates Program, administered jointly by the ORNL and the Oak Ridge Institute for Science and Education. CIC and NCG acknowledge support from the Materials Science and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy under contract number DE-AC05-00OR22725. The authors thank one anonymous reviewer for constructive queries and suggestions that helped raised the quality of the manuscript. This work was enthusiastically supported by the late Dr. Yuri Melnichenko, who unfortunately did not live to see the results.
Funders | Funder number |
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Scientific User Facilities Division | |
U.S. Department of Energy | DE-AC05-00OR22725 |
Basic Energy Sciences | |
Oak Ridge National Laboratory | |
Oak Ridge Institute for Science and Education | |
Division of Materials Sciences and Engineering |