Atypical hydrogen uptake on chemically-activated, ultramicroporous carbon

Vinay V. Bhat; Cristian I. Contescu; Nidia C. Gallego; Frederick S. Baker

doi:10.1016/j.carbon.2009.12.001

Atypical hydrogen uptake on chemically-activated, ultramicroporous carbon

Vinay V. Bhat, Cristian I. Contescu, Nidia C. Gallego, Frederick S. Baker

Nanomaterials Chemistry Group

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Abstract

Hydrogen adsorption on ultramicroporous carbon was investigated at near-ambient temperatures using volumetric and gravimetric methods. The results showed that the main process, physisorption, is accompanied by a slow process of different nature, that causes slow uptake at high pressures and hysteresis on desorption. The combined result is unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt.% at 25 °C and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17-20 kJ/mol) is higher than usually reported for carbon materials; the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption induced by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.

Original language	English
Pages (from-to)	1331-1340
Number of pages	10
Journal	Carbon
Volume	48
Issue number	5
DOIs	https://doi.org/10.1016/j.carbon.2009.12.001
State	Published - Apr 2010

Funding

This research is supported by the Division of Materials Science and Engineering, U. S. Department of Energy, under contract DE-AC05-00OR22275 with U. T. Battelle, LLC. A portion of this research was conducted at ORNL’s Center for Nanophase Materials Science, which is sponsored by the Scientific Users Facility Division, Office of Basic Energy Sciences, U.S. Department of Energy. The authors acknowledge Dr. A. Lupini (ORNL) for high resolution STEM images. One of the authors (V.V.B.) acknowledges the appointment under ORNL Postdoctoral Associate Program administered jointly by ORISE and ORNL. The authors acknowledge MeadWestvaco Corporation (Charleston, SC) for kindly supplying the UMC sample, and Dr. Karol Putyera’s help (EAG Shiva Technologies, Inc., Syracuse, NY) with GDMS analysis of UMC material.

Funders	Funder number
Division of Materials Science and Engineering
U. S. Department of Energy	DE-AC05-00OR22275
U.S. Department of Energy
Basic Energy Sciences
Oak Ridge National Laboratory
Oak Ridge Institute for Science and Education

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10.1016/j.carbon.2009.12.001

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abstract = "Hydrogen adsorption on ultramicroporous carbon was investigated at near-ambient temperatures using volumetric and gravimetric methods. The results showed that the main process, physisorption, is accompanied by a slow process of different nature, that causes slow uptake at high pressures and hysteresis on desorption. The combined result is unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt.% at 25 °C and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17-20 kJ/mol) is higher than usually reported for carbon materials; the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption induced by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.",

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N2 - Hydrogen adsorption on ultramicroporous carbon was investigated at near-ambient temperatures using volumetric and gravimetric methods. The results showed that the main process, physisorption, is accompanied by a slow process of different nature, that causes slow uptake at high pressures and hysteresis on desorption. The combined result is unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt.% at 25 °C and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17-20 kJ/mol) is higher than usually reported for carbon materials; the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption induced by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.

AB - Hydrogen adsorption on ultramicroporous carbon was investigated at near-ambient temperatures using volumetric and gravimetric methods. The results showed that the main process, physisorption, is accompanied by a slow process of different nature, that causes slow uptake at high pressures and hysteresis on desorption. The combined result is unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt.% at 25 °C and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17-20 kJ/mol) is higher than usually reported for carbon materials; the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption induced by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.

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Atypical hydrogen uptake on chemically-activated, ultramicroporous carbon

Abstract

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