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Title: Mechanism of enhanced hydrogen adsorption on palladium-doped nanoporous carbon fibers

Abstract

Recent work at Oak Ridge National Laboratory was directed towards adsorptive storage of hydrogen in nanoporous carbon fibers in which palladium was incorporated prior to spinning and carbonization/activation of the fibers. Palladium doped carbon fibers exhibited enhanced hydrogen uptake compared to the corresponding palladium-free nanoporous carbon fibers (at room temperature and 2 MPa pressure). However, the mechanism responsible for the enhanced hydrogen uptake is not fully understood. New findings are presented in this paper in support of a mechanism that encompasses both hydrogen spillover on palladium metal sites and hydrogen physisorption on nanostructured carbon sites.

Authors:
 [1];  [1];  [1];  [2];  [2];  [1];  [1]
  1. ORNL
  2. Clemson University
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Temperature Materials Lab. (HTML)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
932064
DOE Contract Number:
AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: Carbon 2007 Conference, Seattle, WA, USA, 20070715, 20070720
Country of Publication:
United States
Language:
English
Subject:
activated carbon; hydrogen storage; spillover

Citation Formats

Contescu, Cristian I, Gallego, Nidia C, Wu, Xianxian, Tekinalp, Halil, Edie, Dan, Thies, Mark C, and Baker, Frederick S. Mechanism of enhanced hydrogen adsorption on palladium-doped nanoporous carbon fibers. United States: N. p., 2007. Web.
Contescu, Cristian I, Gallego, Nidia C, Wu, Xianxian, Tekinalp, Halil, Edie, Dan, Thies, Mark C, & Baker, Frederick S. Mechanism of enhanced hydrogen adsorption on palladium-doped nanoporous carbon fibers. United States.
Contescu, Cristian I, Gallego, Nidia C, Wu, Xianxian, Tekinalp, Halil, Edie, Dan, Thies, Mark C, and Baker, Frederick S. Mon . "Mechanism of enhanced hydrogen adsorption on palladium-doped nanoporous carbon fibers". United States. doi:.
@article{osti_932064,
title = {Mechanism of enhanced hydrogen adsorption on palladium-doped nanoporous carbon fibers},
author = {Contescu, Cristian I and Gallego, Nidia C and Wu, Xianxian and Tekinalp, Halil and Edie, Dan and Thies, Mark C and Baker, Frederick S},
abstractNote = {Recent work at Oak Ridge National Laboratory was directed towards adsorptive storage of hydrogen in nanoporous carbon fibers in which palladium was incorporated prior to spinning and carbonization/activation of the fibers. Palladium doped carbon fibers exhibited enhanced hydrogen uptake compared to the corresponding palladium-free nanoporous carbon fibers (at room temperature and 2 MPa pressure). However, the mechanism responsible for the enhanced hydrogen uptake is not fully understood. New findings are presented in this paper in support of a mechanism that encompasses both hydrogen spillover on palladium metal sites and hydrogen physisorption on nanostructured carbon sites.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • Pd-free and Pd-containing activated carbon fibers (Pd-ACF) were synthesized from isotropic pitch as a carbon precursor. The source of Pd was a palladium salt that was premixed with pitch before carbonization. Hydrogen adsorption was measured at near-ambient temperatures (5 to 80 oC) and moderate pressures (up to 20 bar). It was found that adsorption on Pd-ACF is always higher than that on corresponding ACF, and in excess of what it would be expected based solely on formation of Pd hydride. This fact can be explained based on the mechanism of hydrogen spillover. It was also found that temperature and pressuremore » have opposite effects on physisorption and spillover. It was hypothesized that a narrow temperature range exists, where the kinetic advantage of H2 spillover in Pd-ACF overlaps synergistically with the thermodynamic advantage of physisorption, thus contributing to enhanced uptakes compared with the Pd-free carbons.« less
  • Palladium-modified activated carbon fibers (Pd-ACF) are being evaluated for adsorptive hydrogen storage at near-ambient conditions because of their enhanced hydrogen uptake in comparison to Pd-free activated carbon fibers (ACF). The net uptake enhancement (at room temperature and 20 bar) is in excess of the amount corresponding to formation of Pd hydride, and is usually attributed to hydrogen spillover. In this paper, inelastic neutron scattering was used to demonstrate the formation of new C-H bonds in Pd-containing activated carbon fibers after exposure to hydrogen at 20 oC and 1.6 MPa, at the expense of physisorbed H2. This finding is a post-factummore » proof of the atomic nature of H species formed in presence of a Pd catalyst, and of their subsequent spillover and binding to the carbon support. Chemisorption of hydrogen may explain the reduction in hydrogen uptake from first to second adsorption cycle.« less
  • No abstract prepared.