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Hydrogen diffusion in potassium intercalated graphite studied by quasielastic neutron scattering

Purewal, Justin and Keith, J. Brandon and Ahn, Channing C. and Brown, Craig M. and Tyagi, Madhusudan and Fultz, Brent (2012) Hydrogen diffusion in potassium intercalated graphite studied by quasielastic neutron scattering. Journal of Chemical Physics, 137 (22). Art. No. 224704 . ISSN 0021-9606. doi:10.1063/1.4767055.

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The graphite intercalation compound KC24 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 H2 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.

Item Type:Article
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Fultz, Brent0000-0002-6364-8782
Additional Information:© 2012 American Institute of Physics. Received 22 September 2012; accepted 29 October 2012; published online 14 December 2012. The authors thank Ron Cappelletti at NCNR for very helpful discussions, and acknowledge Hillary Smith for help with the QENS measurements. The work benefited from software developed in the DANSE project under National Science Foundation (NSF) Award No. DMR-0520547. This work utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0944772 and was partially supported by the Office of Energy Efficiency and Renewable Energy through the Hydrogen Sorption Center of Excellence under Contract Nos. DE-FC36-05GO15079 and DE-EE0000262. Certain commercial equipment, instruments, materials, or material suppliers are identified in this article to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
Funding AgencyGrant Number
Office of Energy Efficiency and Renewable EnergyDE-FC36-05GO15079
Office of Energy Efficiency and Renewable EnergyDE-EE0000262
Subject Keywords:adsorption; graphite; heat of adsorption; hydrogen; neutron diffraction; potassium compounds; self-diffusion; stoichiometry
Issue or Number:22
Classification Code:PACS: 68.43.Mn; 82.60.-s; 66.30.hp; 61.66.Bi; 61.66.Dk
Record Number:CaltechAUTHORS:20130124-084248748
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Official Citation:Hydrogen diffusion in potassium intercalated graphite studied by quasielastic neutron scattering Justin Purewal, J. Brandon Keith, Channing C. Ahn, Craig M. Brown, Madhusudan Tyagi, and Brent Fultz, J. Chem. Phys. 137, 224704 (2012), DOI:10.1063/1.4767055
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36557
Deposited By: Jason Perez
Deposited On:24 Jan 2013 19:37
Last Modified:09 Nov 2021 23:22

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