The Role of Ti in Alanates and Borohydrides: Catalysis and Metathesis

Callini, Elsa; Borgschulte, Andreas; Hugelshofer, Cedric L.; Ramirez‐Cuesta, Anibal J.; Zuettel, A.

doi:10.1021/jp407999r

Cited by 24 publications

(26 citation statements)

References 54 publications

(71 reference statements)

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“…Recently, the formation of a volatile Ti(BH 4 ) 3 on the surface of the sample during the metathesis TiCl 3 ? LiBH 4 [186,187] was investigated to better understand the role of the TiCl 3 addition [188]. The metathesis produces Ti(BH 4 ) 3 and LiCl.…”

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Complex and liquid hydrides for energy storage

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The research on complex hydrides for hydrogen storage was initiated by the discovery of Ti as a hydrogen sorption catalyst in NaAlH 4 by Boris Bogdanovic in 1996. A large number of new complex hydride materials in various forms and combinations have been synthesized and characterized, and the knowledge regarding the properties of complex hydrides and the synthesis methods has grown enormously since then. A significant portion of the research groups active in the field of complex hydrides is collaborators in the International Energy Agreement Task 32. This paper reports about the important issues in the field of complex hydride research, i.e. the synthesis of borohydrides, the thermodynamics of complex hydrides, the effects of size and confinement, the hydrogen sorption mechanism and the complex hydride composites as well as the properties of liquid complex hydrides. This paper is the result of the collaboration of several groups and is an excellent summary of the recent achievements.

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“…Some effects of Ti compound of the addition to borohydrides [4] have been shown. [5] However, the hydrogen desorption reaction from borohydrides is not catalysed by Ti, when the system is exposed to a gas flow, [6] as presented in Fig. 1.…”

Section: Hydrogen Storage In Complex Hydridesmentioning

confidence: 99%

Surface Reactions are Crucial for Energy Storage

Callini

Kato

Mauron

et al. 2015

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Reactions between gas molecules, e.g. H2 and CO2 and solids take place at the surface. The electronic states and the local geometry of the atomic arrangement determine the energy of the adsorbate, i.e. the initial molecule and the transition state. Here we review our research to identify the surface species, their chemical state and orientation, the interaction with the neighbouring molecules and the mobility of the adsorbed species and complement the experimental results with thermodynamic modelling. The role of the Ti was found to be a bridge between the charged species preventing the individual movement of the ions including charge separation. The Ti has no catalytic effect on the hydrogen sorption reaction in borohydrides. The physisorption of molecular hydrogen is too weak at ambient temperature to reach a significant hydrogen storage density. The addition of a hydrogen dissociation catalyst to a nanoporous material with a large specific surface area may potentially enable the spillover of hydrogen atoms from the metal catalyst to the surface of the porous material and chemisorb on specific sites with a much higher binding energy compared to physisorption. The intercalation of alkali metals in C60 fullerenes increases the interaction energy of hydrogen with the so-called metal fullerides significantly. Sterical diffusion barriers by partial oxidation of the surface of borohydrides turned out to redirect the reaction path towards pure hydrogen desorption and suppress the formation of diborane, a by-product of the hydrogen evolution reaction from borohydrides previously undetected. The combination of a newly developed gas controlling system with microreactors allows us to investigate complex reactions with small quantities of nano designed new catalytic materials. Furthermore, tip-enhanced Raman spectroscopy (TERS) will allow the investigation of the reactions locally on the surface of the catalyst and the near ambient pressure photoelectron spectroscopy enables analysis of the surfaces in ultra-high vacuum and in situ interaction with the adsorbates i.e. while the reaction takes place. This brings us in a unique position for the investigation of the heterogeneous reactive systems. The mechanism of the Ti catalysed hydrogen sorption reactions in alanates was recently established based on spectroscopic investigations combined with thermodynamic analysis of the transition states.

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“…19 It is a volatile solid and XRD pattern confirms that the molecular structure of Ti(BH 4 ) 3 is similar to the Al(BH 4 ) 3 structure. 20 The Ti(BH 4 ) 3 .5NH 3 structure has a space group of P222 or P222 1 and each Ti is surrounded by three (-BH 4 ) groups. 21 1652…”

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confidence: 99%

Role of Ti doping and Al and B vacancies in the dehydrogenation of Al(BH4)3

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Metal borohydrides such as Al(BH 4) 3 is thermodynamically very stable but has weak dehydrogenation property. In contrast, Ti(BH 4) 3 has less stability (25 • C) but excellent dehydrogenation property. Hence, we have studied Ti-doped aluminium borohydride systems in order to improve the dehydrogenation property. Our density functional studies (DOS and pDOS) show that Ti interacts more strongly with the BH 4 unit and such strong interaction weakens the B-H bond and improves the dehydrogenation property. Ti-doped Al(BH 4) 3 system improves the overall stability due to the formation of a stronger Ti-B bond. Our study on defects in Al(BH 4) 3 suggests that B-defect system has the best dehydrogenation property compared to the pure and Ti-doped Al(BH 4) 3 systems.

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The Role of Ti in Alanates and Borohydrides: Catalysis and Metathesis

Cited by 24 publications

References 54 publications

Complex and liquid hydrides for energy storage

Complex and liquid hydrides for energy storage

Surface Reactions are Crucial for Energy Storage

Role of Ti doping and Al and B vacancies in the dehydrogenation of Al(BH4)3

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