Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

The prerequisite for widespread use of hydrogen as an energy carrier is the development of new materials that can safely store it at high gravimetric and volumetric densities. Metal borohydrides M(BH4)n (n is the valence of metal M), in particular, have high hydrogen density, and are therefore regarded as one such potential hydrogen storage material. For fuel cell vehicles, the goal for on-board storage systems is to achieve reversible store at high density but moderate temperature and hydrogen pressure. To this end, a large amount of effort has been devoted to improvements in their thermodynamic and kinetic aspects. This review provides an overview of recent research activity on various M(BH4)n, with a focus on the fundamental dehydrogenation and rehydrogenation properties and on providing guidance for material design in terms of tailoring thermodynamics and promoting kinetics for hydrogen storage.

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Recent Progress in Metal Borohydrides for Hydrogen Storage

Knowledge and foundational understanding of phenomena associated with the behavior of materials at the nanoscale is one of the key scientific challenges toward a sustainable energy future. Size reduction from bulk to the nanoscale leads to a variety of exciting and anomalous phenomena due to enhanced surface-to-volume ratio, reduced transport length, and tunable nanointerfaces. Nanostructured metal hydrides are an important class of materials with significant potential for energy storage applications. Hydrogen storage in nanoscale metal hydrides has been recognized as a potentially transformative technology, and the field is now growing steadily due to the ability to tune the material properties more independently and drastically compared to those of their bulk counterparts. The numerous advantages of nanostructured metal hydrides compared to bulk include improved reversibility, altered heats of hydrogen absorption/desorption, nanointerfacial reaction pathways with faster rates, and new surface states cap...

Nanostructured Metal Hydrides for Hydrogen Storage.

A wide variety of metal borohydrides, MBH4, have been discovered and characterized during the past decade, revealing an extremely rich chemistry including fascinating structural flexibility and a wide range of compositions and physical properties. Metal borohydrides receive increasing interest within the energy storage field due to their extremely high hydrogen density and possible uses in batteries as solid state ion conductors. Recently, new types of physical properties have been explored in lanthanide-bearing borohydrides related to solid state phosphors and magnetic refrigeration. Two major classes of metal borohydride derivatives have also been discovered: anion-substituted compounds where the complex borohydride anion, BH4−, is replaced by another anion, i.e. a halide or amide ion; and metal borohydrides modified with neutral molecules, such as NH3, NH3BH3, N2H4, etc. Here, we review new synthetic strategies along with structural, physical and chemical properties for metal borohydrides, revealing a number of new trends correlating composition, structure, bonding and thermal properties. These new trends provide general knowledge and may contribute to the design and discovery of new metal borohydrides with tailored properties towards the rational design of novel functional materials. This review also demonstrates that there is still room for discovering new combinations of light elements including boron and hydrogen, leading to complex hydrides with extreme flexibility in composition, structure and properties.

Metal borohydrides and derivatives – synthesis, structure and properties

Hydrogen is recognized as a possible future energy carrier, which can be produced from renewable energy and water. A major challenge in a future ‘hydrogen economy’ is the development of safe, compact, robust, and efficient means of hydrogen storage, in particular for mobile applications. The present review focuses on light metal boron based hydrides, for which the general interest has expanded significantly during the past few years. Synthesis methods, physical, chemical and structural properties of novel boron based hydrides are reviewed along with new approaches for improving kinetic and thermodynamic properties: (i) anion substitution, (ii) reactive hydride composites and (iii) nanoconfinement of hydrides and chemical reactions. The light metal borohydrides reveal a fascinating structural chemistry and have the potential for storing large amounts of hydrogen. A combination of the different approaches may provide a new route to a wide range of interesting energy storage materials in the future.

Tailoring properties of borohydrides for hydrogen storage: A review

Reactive hydride composites (RHCs) are very promising hydrogen storage materials for future applications due to their reduced reaction enthalpies and high gravimetric capacities. At present, the materials' functionality is limited by the reaction kinetics. A significant positive influence can be observed with addition of transition-metal-based additives. To understand the effect of these additives, the chemical state and changes during the reaction as well as the microstructural distribution were investigated using x-ray absorption near-edge structure (XANES) spectroscopy and anomalous small-angle x-ray scattering (ASAXS). In this work, zirconium- and vanadium-based additives were added to 2LiBH4–MgH2 composites and 2LiH–MgB2 composites and measured in the vicinity of the corresponding absorption edge. The measurements reveal the formation of finely distributed zirconium diboride and vanadium-based nanoparticles. The potential mechanisms for the observed influence on the reaction kinetics are discussed.

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On the chemical state and distribution of Zr- and V-based additives in reactive hydride composites

Effect of Fe additive on the hydrogenation-dehydrogenation properties of 2LiH + MgB2/2LiBH4 + MgH2 system

Several different evaluation methods (EM) to obtain the band gap energy (Eg) of semiconductors via UV/Vis diffuse reflectance spectroscopy (DRS) are used in literature and no clear consensus which EM to use is established. By using P25 as a model semiconductor, evaluating 32 literature sources and our own experiments, we show that the determined Eg energy is heavily influenced by the EM (differences in Eg of up to 0.87 eV). For P25 loaded with CuO even contradictive effects of metal loading on the Eg are observed using different EM. Different phase compositions of TiO2 are also shown to yield EM-dependent results. This paper thus comprehensively investigates the most common EM on different relevant photocatalyst material classes, illustrates their mathematical and graphical determination, gives recommendations which method to use based on a quantitative indicator and illustrates common pitfalls in determining Eg via UV/Vis DRS. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/cptc.202300001

E. Welter

Papers

On the chemical state and distribution of Zr- and V-based additives in reactive hydride composites

Effect of Fe additive on the hydrogenation-dehydrogenation properties of 2LiH + MgB2/2LiBH4 + MgH2 system

Methodological Investigation of the Band Gap Determination of Solid Semiconductors via UV/Vis Spectroscopy