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Infrared spectroscopy as a convenient tool for investigation of hydrogen sorption mechanisms and bonding in complex hydrides

Biliškov, Nikola (2014) Infrared spectroscopy as a convenient tool for investigation of hydrogen sorption mechanisms and bonding in complex hydrides. In: Infrared spectroscopy: theory, developments and applications. Nova Science Publishers, pp. 343-382.

Abstract

A safe, reliable and inexpensive method for solid-state hydrogen storage and transportation is paramount of the challenges that are still to be met to enable the widespread use of hydrogen as a technologically relevant energy carrier. This need has prompted a massive effort in the synthesis and throughout characterisation of novel hydrides and better understanding of these materials and mechanisms of hydrogen absorption and desorption. This knowledge, in turn, follows to rational-based further improvement of solid-state materials for hydrogen storage. Here is given a critical review of experimental and computational infrared spectroscopy (IR) of metal hydride complexes. The included techniques are transmission, attenuated total reflection, diffuse reflection, photoacoustic, variable temperature and variable pressure IR. The advantage of IR spectroscopy lies in its flexibility. It is not restricted to crystalline systems, allowing the observation of amorphous and nanocrystalline materials. Furthermore, it allows in-situ follow-up of hydrogen sorption processes with respect not only to amount of hydrogen, but also ambient pressure and temperature. Changes in the bands due to the metal-hydrogen stretching and bending vibrations corresponding to specific functional groups in the mid-IR region leads to detection of reaction intermediates and phase transitions. This approach, giving a direct insight at molecular level, shows favourable features compared to adsorption/desorption calorimetry or to other classical methods. On the other hand, quantum chemical calculations sinergistically support the experimental IR spectroscopy. Namely, comparison of computed and experimental spectra provides an unambigious assignment of spectra and gives a unique and very clear insight into the microscopic background of observed features. This review is focused on transition metal hydrides, alkali metal, alkaline earth and aluminium compounds with borohydride ion and alkali metal and alkaline earth alanates. They are all ionic or covalent complex hydrides, as opposed to hydrogen-in-metal systems, where hydrogen occupies interstitial sites. Although the central atom of complex hydrides predominantly determines its properties, counter-ion often determines the stability of the material, providing a fine tuning of the hydrogen-sorption behaviour. Thus, the understanding of a role played by counter-ion and the nature of bonding is crucial with regard to rational tailoring of the properties of material. Among the materials for solid-state hydrogen storage, complex light-metal hydrides, especially borohydrides and alanates experienced a renaissance in a last few years. Considerable improvement of their hydrogen sorption behaviour is achieved, especially by restriction of their particle size to nanodimensions and by addition of catalyticaly-active impurities. Although these achievements launched them to the most promising systems for technologically relevant solid-state hydrogen storage, crucial mechanistic details are still unclear. IR spectroscopy, by giving a direct microscopic insight into the sample, provides a unique opportunity to clarify these aspects of operation of complex hydrides, which are of crucial importance with respect of hydrogen storage.

Item Type: Book Section
Uncontrolled Keywords: Infrared spectroscopy; complex hydrides; alanates; borohydrides; amides; amidoboranes; ammonia borane; hydrogen storage
Subjects: NATURAL SCIENCES
NATURAL SCIENCES > Chemistry
NATURAL SCIENCES > Chemistry > Physical Chemistry
NATURAL SCIENCES > Chemistry > Inorganic Chemistry
Divisions: Division of Materials Chemistry
Projects:
Project titleProject leaderProject codeProject type
Metalni hidridi u čistim energetskim sustavima[28751] Antun Drašner098-0982904-2941MZOS
Depositing User: Nikola Biliškov
Date Deposited: 10 Apr 2014 11:15
Last Modified: 10 Apr 2014 11:15
URI: http://fulir.irb.hr/id/eprint/894

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