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Chemical State, Distribution, and Role of Ti- and Nb-Based Additives on the Ca(BH4)2System

Bonatto Minella, Christian and Pellicer, Eva and Rossinyol, Emma and Karimi, Fahim and Pistidda, Claudio and Garroni, Sebastiano and Milanese, Chiara and Nolis, Pau and Baró, Maria Dolors and Gutfleisch, Oliver and Pranzas, Klaus P. and Schreyer, Andreas and Klassen, Thomas and Bormann, Rüdiger and Dornheim, Martin (2013):
Chemical State, Distribution, and Role of Ti- and Nb-Based Additives on the Ca(BH4)2System.
In: The Journal of Physical Chemistry C, ACS Publications, pp. 4394-4403, 117, (9), ISSN 1932-7447,
[Online-Edition: http://dx.doi.org/10.1021/jp3116275],
[Article]

Abstract

Light metal tetrahydroborates are regarded as promising materials for solid state hydrogen storage. Due to both a high gravimetric hydrogen capacity of 11.5 wt % and an ideal dehydrogenation enthalpy of 32 kJ mol–1 H2, Ca(BH4)2 is considered to be one of the most interesting compounds in this class of materials. In this work, a comprehensive investigation of the effect of different selected additives (TiF4, NbF5, Ti-isopropoxide, and CaF2) on the reversible hydrogenation reaction of calcium borohydride is presented combining different investigation techniques. The chemical state of the Nb- and Ti-based additives is studied by X-ray absorption spectroscopy (e.g., XANES). Transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy-dispersive X-ray spectroscopy (EDX) was used to show the local structure, size, and distribution of the additive/catalyst. 11B{1H} solid state magic angle spinning-nuclear magnetic resonance (MAS NMR) was carried out to detect possible amorphous phases. The formation of TiB2 and NbB2 nanoparticles was observed after milling or upon sorption reactions of the Nb- and Ti-based Ca(BH4)2 doped systems. The formation of transition-metal boride nanoparticles is proposed to support the heterogeneous nucleation of CaB6. The {111}CaB6/{1011}NbB2, {111}CaB6/{1010}NbB2, as well as {111}CaB6/{1011}TiB2 plane pairs have the potential to be the matching planes because the d-value mismatch is well below the d-critical mismatch value (6%). Transition-metal boride nanoparticles act as heterogeneous nucleation sites for CaB6, refine the microstructure thus improving the sorption kinetics, and, as a consequence, lead to the reversible formation of Ca(BH4)2.

Item Type: Article
Erschienen: 2013
Creators: Bonatto Minella, Christian and Pellicer, Eva and Rossinyol, Emma and Karimi, Fahim and Pistidda, Claudio and Garroni, Sebastiano and Milanese, Chiara and Nolis, Pau and Baró, Maria Dolors and Gutfleisch, Oliver and Pranzas, Klaus P. and Schreyer, Andreas and Klassen, Thomas and Bormann, Rüdiger and Dornheim, Martin
Title: Chemical State, Distribution, and Role of Ti- and Nb-Based Additives on the Ca(BH4)2System
Language: English
Abstract:

Light metal tetrahydroborates are regarded as promising materials for solid state hydrogen storage. Due to both a high gravimetric hydrogen capacity of 11.5 wt % and an ideal dehydrogenation enthalpy of 32 kJ mol–1 H2, Ca(BH4)2 is considered to be one of the most interesting compounds in this class of materials. In this work, a comprehensive investigation of the effect of different selected additives (TiF4, NbF5, Ti-isopropoxide, and CaF2) on the reversible hydrogenation reaction of calcium borohydride is presented combining different investigation techniques. The chemical state of the Nb- and Ti-based additives is studied by X-ray absorption spectroscopy (e.g., XANES). Transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy-dispersive X-ray spectroscopy (EDX) was used to show the local structure, size, and distribution of the additive/catalyst. 11B{1H} solid state magic angle spinning-nuclear magnetic resonance (MAS NMR) was carried out to detect possible amorphous phases. The formation of TiB2 and NbB2 nanoparticles was observed after milling or upon sorption reactions of the Nb- and Ti-based Ca(BH4)2 doped systems. The formation of transition-metal boride nanoparticles is proposed to support the heterogeneous nucleation of CaB6. The {111}CaB6/{1011}NbB2, {111}CaB6/{1010}NbB2, as well as {111}CaB6/{1011}TiB2 plane pairs have the potential to be the matching planes because the d-value mismatch is well below the d-critical mismatch value (6%). Transition-metal boride nanoparticles act as heterogeneous nucleation sites for CaB6, refine the microstructure thus improving the sorption kinetics, and, as a consequence, lead to the reversible formation of Ca(BH4)2.

Journal or Publication Title: The Journal of Physical Chemistry C
Volume: 117
Number: 9
Publisher: ACS Publications
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 10 Mar 2014 09:15
Official URL: http://dx.doi.org/10.1021/jp3116275
Identification Number: doi:10.1021/jp3116275
Funders: The authors are grateful to the Marie-Curie European Research Training Network (Contract MRTN- CT-2006-03 5366/ COSY) and to the German Bundesministerium für Bildung und Forschung (Förderkennzeichen 03BV108C) for the financial support. , E.P., E.R., M.D.B. acknowledge the financial support of 2009-SGR-1292., M.D.B. thanks partial financial support from an ICREA-Academia award.
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