Complex hydrides for energy storage

In the past decades, complex hydrides and complex hydrides-based materials have been thoroughly investigated as materials for energy storage, owing to their very high gravimetric and volumetric hydrogen capacities and interesting cation and hydrogen diffusion properties. Concerning hydrogen storage, the main limitations of this class of materials are the high working temperatures and pressures, the low hydrogen absorption and desorption rates and the poor cyclability. In the past years, research in this field has been focused on understanding the hydrogen release and uptake mechanism of the pristine and catalyzed materials and on the characterization of the thermodynamic aspects, in order to rationally choose the composition and the stoichiometry of the systems in terms of hydrogen active phases and catalysts/destabilizing agents. Moreover, new materials have been discovered and characterized in an attempt to find systems with properties suitable for practical on-board and stationary applications. A significant part of this rich and productive activity has been performed by the research groups led by the Experts of the International Energy Agreement Task 32, often in collaborative research projects. The most recent findings of these joint activities and other noteworthy recent results in the field are reported in this paper

Solvent-free synthesis and decomposition of Y(BH4)(3)

The direct and solvent-free synthesis of yttrium borohydride was achieved by reactive ball milling of yttrium hydride in diborane/hydrogen atmosphere. The product contains only the solid elemental hydride as remaining contaminant. Yields above 75% were obtained. The product crystallizes in the cubic α phase and releases hydrogen above 460 K. The decomposition was measured by in situ X-ray diffraction and the hydrogen release was monitored gravimetrically in conjunction with infrared gas analysis. No diborane was detected during the decomposition. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

High-pressure and high-temperature x-ray diffraction cell for combined pressure, composition, and temperature measurements of hydrides

We present the design and construction of a high-pressure (200 bars) and high-temperature (600 °C) x-ray diffraction (XRD) cell for the in situ investigation of the hydrogen sorption of hydrides. In combination with a pressure, composition, and temperature system, simultaneous XRD and volumetric measurements become accessible. The cell consists of an x-ray semi-transparent hemispherical beryllium (Be) dome covering a heatable sample stage, which simultaneously allows sample temperatures of up to 600 °C in an applied hydrogen atmosphere of up to 200 bars. The system volume is as low as possible to maximize the precision of the volumetric measurements. Due to the high thermal conductivity of hydrogen, and in order to preserve the mechanical stability of the beryllium, the cell is water cooled. Its operability was studied on the example of the hydrogen absorption of Mg 2Ni. The advantages and limitations of the proposed design are discussed. © 2011 American Institute of Physics

Hydrogen tracer diffusion in LiBH(4) measured by spatially resolved Raman spectroscopy

The hydrogen tracer diffusion in LiBH4 has been determined by spatially resolved Raman spectroscopy. The measurements give direct evidence of a macroscopic diffusion of BH-4 ions as well as atomic exchange of hydrogen between the anions. An effective tracer diffusion coefficient of deuterium in LiBH4 of D ≃ 7 × 10-14m2 s -1 at 473 K is derived. The direct exchange rate of hydrogen between BH4 units is 10 orders of magnitude slower, i.e. the relatively fast effective hydrogen diffusion has its origin in the fast diffusion of BH 4 units. © 2010 The Owner Societies

Seasonal energy storage system based on hydrogen for self sufficient living

SELF is a resource independent living and working environment. By on-board renewable electricity generation and storage, it accounts for all aspects of living, such as space heating and cooking as well as providing a purified rainwater supply and wastewater treatment, excluding food supply. Uninterrupted, on-demand energy and water supply are the key challenges. Off-grid renewable power supply fluctuations on daily and seasonal time scales impose production gaps that have to be served by local storage, a function normally fulfilled by the grid. While daily variations only obligate a small storage capacity, requirements for seasonal storage are substantial. The energy supply for SELF is reviewed based on real meteorological data and demand patterns for Zurich, Switzerland. A battery system with propane for cooking serves as a reference for battery-only and hybrid battery/hydrogen systems. In the latter, hydrogen is used for cooking and electricity generation. The analysis shows that hydrogen is ideal for long term bulk energy storage on a seasonal timescale, while batteries are best suited for short term energy storage. Although the efficiency penalty from hydrogen generation is substantial, in off-grid systems, this parameter is tolerable since the harvesting ratio of photovoltaic energy is limited by storage capacity. © 2010 Elsevier B.V. All rights reserved