title: The influence of dispersion interactions on the hydrogen adsorption properties of expanded graphite.
abstract: We demonstrate the importance of London dispersion forces in defining the adsorption capacity within expanded graphite, a simple model of the more complex experimental geometries of activated carbon, using a combination of the non-local correlation functional of Dion et al paired with a recent exchange functional of Cooper (vdW-DF(C09x)) and a classical continuum model. Our results indicate that longer ranged interactions due to dispersion forces increase the volume over which molecules interact with a porous medium. This significantly enhances the adsorption density within a material, and explains recent experimental work showing that the densification of H(2) in carbon nanopores is sensitive to the pore size. Remarkably, our slit pore geometries give adsorption densities of up to 3 wt% at 298 K and 20 MPa which correlates well with experimental values for 9 Å pores-a value that could not be predicted using local density approximation (LDA) calculations. In its entirety, this work presents a powerful approach for assessing molecular uptake in porous media and may have serious impacts on efforts to optimize the properties of these materials.
authors.affiliation: Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: Yungok
authors.initials: Y
authors.lastname: Ihm
authors.forename: Valentino R
authors.initials: VR
authors.lastname: Cooper
authors.forename: Lujian
authors.initials: L
authors.lastname: Peng
authors.forename: James R
authors.initials: JR
authors.lastname: Morris
mesh_terms: D000327:Adsorption; D002244:Carbon / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008956:Models, Chemical; D058608:Nanopores; D016062:Porosity; D013499:Surface Properties
chemical_list: D002244:Carbon; D006108:Graphite; D006859:Hydrogen