Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published February 1, 2009 | Published
Journal Article Open

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

Files

Purewal2009p60010.1103PhysRevB.79.054305.pdf
Files (359.4 kB)
Name Size Download all
md5:0234c07dbef1f15000b7c96664730fcf
359.4 kB Preview Download

Additional details

Created:
August 20, 2023
Modified:
October 19, 2023