Purewal, J. J. and Keith, J. B. and Ahn, C. C. and Fultz, B. and Brown, C. M. and Tyagi, M. (2009) Adsorption and melting of hydrogen in potassium-intercalated graphite. Physical Review B, 79 (5). Art. No. 054305. ISSN 1098-0121 http://resolver.caltech.edu/CaltechAUTHORS:20090831-151955826
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Volumetric adsorption and quasielastic neutron scattering are used to study the diffusion and thermodynamics of sorbed H_2 in the graphite intercalation compound KC24. A sorption enthalpy of 8.5 kJ/mol at zero coverage is determined from H_2 adsorption isotherms. From measurements of total elastic-neutron-scattering intensity as a function of temperature, a melting transition of the H_2 adsorbate is observed at 35 K for KC_(24)(H_2)_1. Quasielastic-neutron-scattering (QENS) spectra reveal distinct slow- and fast-H_2-diffusion processes which exist simultaneously at temperatures above the transition point. The temperature dependence of the characteristic diffusion times follows an Arrhenius relation tau=tau_0 exp(E_a/T), where tau_0^(fast)=1.0±0.1 ps, tau_0^(slow)=21±2 ps, E_a^(fast)=156±5 K, and E_a^(slow)=189±5 K. The fast-diffusion process is attributable to individual motions of H_2 molecules in a static potassium structure, and the slow-diffusion process could be attributable to fluctuations in H_2 particle density correlated with jumps of potassium atoms. The QENS spectra at low Q are used to discuss the dimensionality of the diffusion process.
|Additional Information:||©2009 The American Physical Society. Received 17 October 2008; revised 21 January 2009; published 27 February 2009. This work utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0454672 and was partially supported by the Office of Energy Efficiency and Renewable Energy through the Hydrogen Sorption Center of Excellence under Contract No. DE-FC36-05GO15079. # 34.35.+a Interactions of atoms and molecules with surfaces # 78.70.Nx Neutron inelastic scattering (condensed matter) # 82.75.Jn Measurements and modeling of molecule migration in zeolites|
|Subject Keywords:||adsorption, diffusion, enthalpy, graphite intercalation compounds, hydrogen, melting, neutron diffraction, potassium compounds, spectral line intensity|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||George Porter|
|Deposited On:||08 Sep 2009 22:47|
|Last Modified:||26 Dec 2012 11:17|
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