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Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures

Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures
Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures

A sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius-Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius-Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius-Clapeyron and Clapeyron equations from hydrogen sorption data for two materials - activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius-Clapeyron equation can only be used at low coverage, since hydrogen's behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius-Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters.

Hydrogen storage, Isosteric enthalpies of adsorption, Physisorption, Porous materials, Storage systems, Thermal management
0929-5607
373-384
Bimbo, Nuno
53d9fc24-e2c1-4e2d-8d75-8dc640d8adda
Sharpe, Jessica E.
c8f4c69d-b116-49d1-ab40-71a5807b6a59
Ting, Valeska P.
d4381878-2aad-4a3f-a7cc-021a7f7075eb
Noguera-Díaz, Antonio
bea37c4d-bae4-4946-98b4-9a3c367d94e4
Mays, Timothy J.
d02351c7-1d8f-4a9e-8d16-675c1f7b3635
Bimbo, Nuno
53d9fc24-e2c1-4e2d-8d75-8dc640d8adda
Sharpe, Jessica E.
c8f4c69d-b116-49d1-ab40-71a5807b6a59
Ting, Valeska P.
d4381878-2aad-4a3f-a7cc-021a7f7075eb
Noguera-Díaz, Antonio
bea37c4d-bae4-4946-98b4-9a3c367d94e4
Mays, Timothy J.
d02351c7-1d8f-4a9e-8d16-675c1f7b3635

Bimbo, Nuno, Sharpe, Jessica E., Ting, Valeska P., Noguera-Díaz, Antonio and Mays, Timothy J. (2014) Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures. Adsorption, 20 (2-3), 373-384. (doi:10.1007/s10450-013-9575-7).

Record type: Article

Abstract

A sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius-Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius-Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius-Clapeyron and Clapeyron equations from hydrogen sorption data for two materials - activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius-Clapeyron equation can only be used at low coverage, since hydrogen's behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius-Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters.

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More information

Accepted/In Press date: 11 September 2013
e-pub ahead of print date: 1 October 2013
Published date: 1 February 2014
Keywords: Hydrogen storage, Isosteric enthalpies of adsorption, Physisorption, Porous materials, Storage systems, Thermal management

Identifiers

Local EPrints ID: 435204
URI: http://eprints.soton.ac.uk/id/eprint/435204
ISSN: 0929-5607
PURE UUID: 930cdba5-c024-4704-968e-ec1b0c40f96c
ORCID for Nuno Bimbo: ORCID iD orcid.org/0000-0001-8740-8284

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Date deposited: 25 Oct 2019 16:30
Last modified: 07 Oct 2020 02:26

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Contributors

Author: Nuno Bimbo ORCID iD
Author: Jessica E. Sharpe
Author: Valeska P. Ting
Author: Antonio Noguera-Díaz
Author: Timothy J. Mays

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