Hydrogen storage in porous cyanometalates: role of the exchangeable alkali metal

L. Reguera, J. Balmaseda, L. F. Del Castillo, E. Reguera

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Abstract

The hydrogen storage in zeolite-like hexacyanometalates with different exchangeable alkali metals within the cavities was studied. The H 2 adsorption isotherms were recorded at 75 and 85 K in order to estimate the involved adsorption heats using the isosteric method. The electric field gradient within the porous framework favors the hydrogen adsorption in the materials under study but also could lead to kinetic effects for the pore filling. Such effects were particularly pronounced for sodium among the studied compositions: Zn 3 A 2 [Fe-(CN) 6 ] 2 (A = Na + , K + , Rb + , Cs + ) and Zn 3 [Co(CN) 6 ] 2 . For Na + , a strong interaction with the H 2 molecule takes place, where appreciable kinetic effects even at 258 K are observed. For Zn 3 [Co(CN) 6 ] 2 (rhombohedral phase) where the cavities are free of exchangeable metal and, in consequence, have a weak electric field gradient on their surface, the largest hydrogen storage capacity, close to 12 H 2 molecules per cavity (1.82% by weight), was observed. The hydrogen adsorption in these materials involves adsorption heats in the 6-8.5 kJ/mol range, following the order K > Rb > Cs ≈ Zn 3 [Co(CN) 6 ] 2 . The porous framework of this family of materials is formed by ellipsoidal cavities communicated by elliptical windows. The alkali metals are sited close to the windows. The pore accessibility and pore volume were evaluated from CO 2 adsorption isotherms recorded at 273 K. The free volume was found to be accessible to the CO 2 molecule for all of the studied compositions. According to the obtained isotherms the stabilization of the CO 2 molecule within the pores is caused by the electrostatic interaction between the electric field gradient at the cavity and the adsorbate quadrupole moment. The estimated strength for the guest-host interaction and the accessible pore volume follow the order Na > K > Rb > Cs. The largest accessible pore volume was found for Zn 3 [Co(CN) 6 ] 2 , close to 8 CO 2 molecules per cavity (28% by weight), but with the weaker guest-host interaction. The materials under study were characterized from X-ray diffraction, thermo-gravimetric, infrared, and Mössbauer data. The obtained results shed light on the role of the electric field gradient at the cavity for the hydrogen adsorption. © 2008 American Chemical Society.
Original languageAmerican English
Pages (from-to)5589-5597
Number of pages9
JournalJournal of Physical Chemistry C
DOIs
StatePublished - 10 Apr 2008

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Alkali Metals
Hydrogen storage
Alkali metals
alkali metals
Carbon Monoxide
Adsorption
cavities
Molecules
adsorption
Electric fields
porosity
hydrogen
Hydrogen
Adsorption isotherms
gradients
isotherms
electric fields
molecules
Zeolites
Kinetics

Cite this

@article{56a36f8d0de94cf3a43c640359d9e56a,
title = "Hydrogen storage in porous cyanometalates: role of the exchangeable alkali metal",
abstract = "The hydrogen storage in zeolite-like hexacyanometalates with different exchangeable alkali metals within the cavities was studied. The H 2 adsorption isotherms were recorded at 75 and 85 K in order to estimate the involved adsorption heats using the isosteric method. The electric field gradient within the porous framework favors the hydrogen adsorption in the materials under study but also could lead to kinetic effects for the pore filling. Such effects were particularly pronounced for sodium among the studied compositions: Zn 3 A 2 [Fe-(CN) 6 ] 2 (A = Na + , K + , Rb + , Cs + ) and Zn 3 [Co(CN) 6 ] 2 . For Na + , a strong interaction with the H 2 molecule takes place, where appreciable kinetic effects even at 258 K are observed. For Zn 3 [Co(CN) 6 ] 2 (rhombohedral phase) where the cavities are free of exchangeable metal and, in consequence, have a weak electric field gradient on their surface, the largest hydrogen storage capacity, close to 12 H 2 molecules per cavity (1.82{\%} by weight), was observed. The hydrogen adsorption in these materials involves adsorption heats in the 6-8.5 kJ/mol range, following the order K > Rb > Cs ≈ Zn 3 [Co(CN) 6 ] 2 . The porous framework of this family of materials is formed by ellipsoidal cavities communicated by elliptical windows. The alkali metals are sited close to the windows. The pore accessibility and pore volume were evaluated from CO 2 adsorption isotherms recorded at 273 K. The free volume was found to be accessible to the CO 2 molecule for all of the studied compositions. According to the obtained isotherms the stabilization of the CO 2 molecule within the pores is caused by the electrostatic interaction between the electric field gradient at the cavity and the adsorbate quadrupole moment. The estimated strength for the guest-host interaction and the accessible pore volume follow the order Na > K > Rb > Cs. The largest accessible pore volume was found for Zn 3 [Co(CN) 6 ] 2 , close to 8 CO 2 molecules per cavity (28{\%} by weight), but with the weaker guest-host interaction. The materials under study were characterized from X-ray diffraction, thermo-gravimetric, infrared, and M{\"o}ssbauer data. The obtained results shed light on the role of the electric field gradient at the cavity for the hydrogen adsorption. {\circledC} 2008 American Chemical Society.",
author = "L. Reguera and J. Balmaseda and {Del Castillo}, {L. F.} and E. Reguera",
year = "2008",
month = "4",
day = "10",
doi = "10.1021/jp7117339",
language = "American English",
pages = "5589--5597",
journal = "Journal of Physical Chemistry C",
issn = "1932-7447",
publisher = "American Chemical Society",

}

Hydrogen storage in porous cyanometalates: role of the exchangeable alkali metal. / Reguera, L.; Balmaseda, J.; Del Castillo, L. F.; Reguera, E.

In: Journal of Physical Chemistry C, 10.04.2008, p. 5589-5597.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Hydrogen storage in porous cyanometalates: role of the exchangeable alkali metal

AU - Reguera, L.

AU - Balmaseda, J.

AU - Del Castillo, L. F.

AU - Reguera, E.

PY - 2008/4/10

Y1 - 2008/4/10

N2 - The hydrogen storage in zeolite-like hexacyanometalates with different exchangeable alkali metals within the cavities was studied. The H 2 adsorption isotherms were recorded at 75 and 85 K in order to estimate the involved adsorption heats using the isosteric method. The electric field gradient within the porous framework favors the hydrogen adsorption in the materials under study but also could lead to kinetic effects for the pore filling. Such effects were particularly pronounced for sodium among the studied compositions: Zn 3 A 2 [Fe-(CN) 6 ] 2 (A = Na + , K + , Rb + , Cs + ) and Zn 3 [Co(CN) 6 ] 2 . For Na + , a strong interaction with the H 2 molecule takes place, where appreciable kinetic effects even at 258 K are observed. For Zn 3 [Co(CN) 6 ] 2 (rhombohedral phase) where the cavities are free of exchangeable metal and, in consequence, have a weak electric field gradient on their surface, the largest hydrogen storage capacity, close to 12 H 2 molecules per cavity (1.82% by weight), was observed. The hydrogen adsorption in these materials involves adsorption heats in the 6-8.5 kJ/mol range, following the order K > Rb > Cs ≈ Zn 3 [Co(CN) 6 ] 2 . The porous framework of this family of materials is formed by ellipsoidal cavities communicated by elliptical windows. The alkali metals are sited close to the windows. The pore accessibility and pore volume were evaluated from CO 2 adsorption isotherms recorded at 273 K. The free volume was found to be accessible to the CO 2 molecule for all of the studied compositions. According to the obtained isotherms the stabilization of the CO 2 molecule within the pores is caused by the electrostatic interaction between the electric field gradient at the cavity and the adsorbate quadrupole moment. The estimated strength for the guest-host interaction and the accessible pore volume follow the order Na > K > Rb > Cs. The largest accessible pore volume was found for Zn 3 [Co(CN) 6 ] 2 , close to 8 CO 2 molecules per cavity (28% by weight), but with the weaker guest-host interaction. The materials under study were characterized from X-ray diffraction, thermo-gravimetric, infrared, and Mössbauer data. The obtained results shed light on the role of the electric field gradient at the cavity for the hydrogen adsorption. © 2008 American Chemical Society.

AB - The hydrogen storage in zeolite-like hexacyanometalates with different exchangeable alkali metals within the cavities was studied. The H 2 adsorption isotherms were recorded at 75 and 85 K in order to estimate the involved adsorption heats using the isosteric method. The electric field gradient within the porous framework favors the hydrogen adsorption in the materials under study but also could lead to kinetic effects for the pore filling. Such effects were particularly pronounced for sodium among the studied compositions: Zn 3 A 2 [Fe-(CN) 6 ] 2 (A = Na + , K + , Rb + , Cs + ) and Zn 3 [Co(CN) 6 ] 2 . For Na + , a strong interaction with the H 2 molecule takes place, where appreciable kinetic effects even at 258 K are observed. For Zn 3 [Co(CN) 6 ] 2 (rhombohedral phase) where the cavities are free of exchangeable metal and, in consequence, have a weak electric field gradient on their surface, the largest hydrogen storage capacity, close to 12 H 2 molecules per cavity (1.82% by weight), was observed. The hydrogen adsorption in these materials involves adsorption heats in the 6-8.5 kJ/mol range, following the order K > Rb > Cs ≈ Zn 3 [Co(CN) 6 ] 2 . The porous framework of this family of materials is formed by ellipsoidal cavities communicated by elliptical windows. The alkali metals are sited close to the windows. The pore accessibility and pore volume were evaluated from CO 2 adsorption isotherms recorded at 273 K. The free volume was found to be accessible to the CO 2 molecule for all of the studied compositions. According to the obtained isotherms the stabilization of the CO 2 molecule within the pores is caused by the electrostatic interaction between the electric field gradient at the cavity and the adsorbate quadrupole moment. The estimated strength for the guest-host interaction and the accessible pore volume follow the order Na > K > Rb > Cs. The largest accessible pore volume was found for Zn 3 [Co(CN) 6 ] 2 , close to 8 CO 2 molecules per cavity (28% by weight), but with the weaker guest-host interaction. The materials under study were characterized from X-ray diffraction, thermo-gravimetric, infrared, and Mössbauer data. The obtained results shed light on the role of the electric field gradient at the cavity for the hydrogen adsorption. © 2008 American Chemical Society.

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DO - 10.1021/jp7117339

M3 - Article

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JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

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