Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 137, Issue 22, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4767055
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Funding
- DANSE project under National Science Foundation (NSF) [DMR-0520547]
- National Science Foundation [DMR-0944772]
- Office of Energy Efficiency and Renewable Energy through the Hydrogen Sorption Center of Excellence [DE-FC36-05GO15079, DE-EE0000262]
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The graphite intercalation compound KC24 adsorbs hydrogen gas at low temperatures up to a maximum stoichiometry of KC24(H-2)(2), with a differential enthalpy of adsorption of approximately -9 kJ mol(-1). The hydrogen molecules and potassium atoms form a two-dimensional condensed phase between the graphite layers. Steric barriers and strong adsorption potentials are expected to strongly hinder hydrogen diffusion within the host KC24 structure. In this study, self-diffusion in a KC24(H-2)(0.5) sample is measured experimentally by quasielastic neutron scattering and compared to values from molecular dynamics simulations. Self-diffusion coefficients are determined by fits of the experimental spectra to a honeycomb net diffusion model and found to agree well with the simulated values. The experimental H-2 diffusion coefficients in KC24 vary from 3.6 x 10(-9) m(2) s(-1) at 80 K to 8.5 x 10(-9) m(2) s(-1) at 110 K. The measured diffusivities are roughly an order of magnitude lower that those observed on carbon adsorbents, but compare well with the rate of hydrogen self-diffusion in molecular sieve zeolites. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4767055]
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