Thermochemical Energy Storage through De/Hydrogenation of Organic Liquids: Reactions of Organic Liquids on Metal Hydrides

Abstract

A study of the reactions of liquid acetone and toluene on transition metal hydrides, which can be used in thermal energy or hydrogen storage applications, is presented. Hydrogen is confined in TiFe, Ti0.95Zr0.05Mn1.49V0.45Fe0.06 ("Hydralloy C5"), and V40Fe8Ti26Cr26 after contact with acetone. Toluene passivates V40Fe8Ti26Cr26 completely for hydrogen desorption while TiFe is only mildly deactivated and desorption is not blocked at all in the case of Hydralloy C5. LaNi5 is inert toward both organic liquids. Gas chromatography (GC) investigations reveal that CO, propane, and propene are formed during hydrogen desorption from V40Fe8Ti26Cr26 in liquid acetone, and methylcyclohexane is formed in the case of liquid toluene. These reactions do not occur if dehydrogenated samples are used, which indicates an enhanced surface reactivity during hydrogen desorption. Significant amounts of carbon-containing species are detected at the surface and subsurface of acetone- and toluene-treated V40Fe8Ti26Cr26 by X-ray photoelectron spectroscopy (XPS). The modification of the surface and subsurface chemistry and the resulting blocking of catalytic sites is believed to be responsible for the containment of hydrogen in the bulk. The surface passivation reactions occur only during hydrogen desorption of the samples.

MgH2/CuxO Hydrogen Storage Composite with Defect-Rich Surfaces for Carbon Dioxide Hydrogenation

“…If a catalyst can provide active sites for the adsorption and activation of CO 2 and also activate H 2 molecule to specific H – or H + , the hydrogenation performance of CO 2 should improve. For CO 2 adsorption, introduction of a defective structure on a nanoscale catalyst should be desirable because this can decrease the coordination of metals facilitating gaseous molecules adsorption and activation. − As for the H 2 activation, an option is to utilize metal-based hydrogen storage material with lattice H – for hydrogenation. , The metal hydrides often have a high catalytic activity in the hydrogenation of ethene, synthesis of ammonia, and hydrogenation of organic liquids. − Using lattice H – as the hydrogen source for CO 2 hydrogenation is different to using molecular H 2 in traditional methods, which should exhibit new hydrogenation characteristics and be of importance for exploring efficient catalysis for CO 2 conversion.…”

Performance Improvement of V–Fe–Cr–Ti Solid State Hydrogen Storage Materials in Impure Hydrogen Gas

“…This corresponds to approximately 1.9 mass% H. It should be noted that the initial heating step was necessary to reactivate the surface sites for hydrogen absorption. Such thermal reactivation treatment has been reported for Ti 1.13 Fe by Hirata et al and by Ulmer et al for V 40 Fe 8 Ti 26 Cr 26 deactivated by organic substances . Hirata et al attribute their observations to the fact that hydrogen desorption is never complete at room temperature, but some of the hydrogen remains absorbed in each cycle.…”

“…Coverage of the surface by impurities hinders access to the catalytic sites either through the formation of a diffusion barrier formed by adsorbed surface species or through the formation of new chemical species, such as metal oxides, which block the catalytic sites necessary to promote hydrogen adsorption and dissociation. This so-called surface “poisoning” effect can have dramatic consequences on the hydriding kinetics and usable capacity. − …”

“…AB-, AB 2 - and AB 5 -type alloys, such as TiFe, ZrV 2 , and LaNi 5 as well as V–Ti-based solid solution alloys have been studied with respect to their behavior upon cycling in impure hydrogen. − ,− Two main conclusions can be drawn from these studies: (1) the tolerance of most metal hydrides toward critical impurities such as oxygen is too low for most technical applications, and (2) LaNi 5 and its related compounds exhibit the highest tolerance toward impurities. The improved tolerance of LaNi 5 toward impurities is linked to its surface properties.…”

“…This improves the high-rate dischargeability of the corresponding Ni-metal hydride battery. 37 Although studies on the surface properties of V−Ti-based solid solution alloys have already been reported, 4,38 our work represents the first thorough investigation that encompasses detailed surface engineering methods and explores the consequences of applying these methods for the hydrogen storage properties in a contaminated H 2 environment. V 40 Fe 8 Ti x Cr y Ni z -based alloys with several different Ti, Cr, and Ni contents were used in this work, aiming to engineer high-capacity, high-performance hydrogen storage alloys.…”