title: Hydrogen diffusion in potassium intercalated graphite studied by quasielastic neutron scattering.
abstract: The graphite intercalation compound KC(24) adsorbs hydrogen gas at low temperatures up to a maximum stoichiometry of KC(24)(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 KC(24) structure. In this study, self-diffusion in a KC(24)(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 KC(24) vary from 3.6 × 10(-9) m(2) s(-1) at 80 K to 8.5 × 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.
authors.affiliation: California Institute of Technology, W. M. Keck Laboratory 138-78, Pasadena, California 91125, USA. jjpurewal@hrl.com
authors.forename: Justin
authors.initials: J
authors.lastname: Purewal
authors.forename: J Brandon
authors.initials: JB
authors.lastname: Keith
authors.forename: Channing C
authors.initials: CC
authors.lastname: Ahn
authors.forename: Craig M
authors.initials: CM
authors.lastname: Brown
authors.forename: Madhusudan
authors.initials: M
authors.lastname: Tyagi
authors.forename: Brent
authors.initials: B
authors.lastname: Fultz