Adsorption and melting of hydrogen in potassium-intercalated graphite
Abstract
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.Attached Files
Published - Purewal2009p60010.1103PhysRevB.79.054305.pdf
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Additional details
- Eprint ID
- 15502
- Resolver ID
- CaltechAUTHORS:20090831-151955826
- DMR-0454672
- NSF
- DE-FC36-05GO15079
- Department of Energy (DOE)
- Created
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2009-09-08Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field