• Energy Research

Abstract Thermal dehydrogenation kinetics of sodium alanate (NaAlH 4 ) has been studied with respect to ZrCl 4 additive, and the results were compared with pure NaAlH 4 . The FTIR analysis has shown insignificant effects of ZrCl 4 on the structural integrity of AlH 4 − anion after ball milling. Partial reduction of ZrCl 4 has been observed during ball milling with NaAlH 4 . The in - situ reduction favors to homogeneous and adherent dropping of ZrCl 4 over the NaAlH 4 surface which leads to remarkably improved dehydrogenation process. The dehydrogenation of ZrCl 4 doped NaAlH 4 occurred in three steps similar to pure NaAlH 4 . The dehydrogenation temperatures of all the steps were substantially decreased as compared to pure NaAlH 4 . The apparent activation energy of dehydrogenation of ZrCl 4 doped NaAlH 4 was evaluated for all the dehydrogenation steps and found to be significantly less with respect to pure NaAlH 4 .

Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The Magnesium group of international experts contributing to IEA Task 32 Hydrogen Based Energy Storage recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications, but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures, kinetics and thermodynamics of the systems based on MgH2,nanostructuring, new Mg-based compounds and novel composites, and catalysis in the Mg based H storage systems. Finally, thermal energy storage and upscaled H storage systems accommodating MgH2 are presented.

Abstract The solar thermal energy could be stored and reused at a desired locations and conditions. The prerequisite is to develop a suitable media which could able to store the solar thermal energy reversibly. The metal-metal hydride system could be one of the option to store the thermal energy in the form of metal and hydrogen which on recombination will form metal- hydride and release the stored thermal energy with high efficiency. Besides the high hydrogen storage capacity, the ultrafast hydrogenation-dehydration kinetics is desirable for the viable commercial applications. In connection to this, magnesium – magnesium hydride system has been considered as a potentials candidate. However, the sluggish hydrogenation-dehydrogenation kinetics is an issue. In the present study nano-engineered Mg-V composite has been developed using MgH2 and V2O5 as a precursor for magnesium and vanadium, respectively. The composite has shown an ultrafast hydrogenation-dehydrogenation kinetics at remarkable low temperature. The hydrogenation of composite has efficiently released the thermal energy. The hydrogenated composite could be dehydrogenated using compact solar power (CSP) even below 200 °C.

Abstract The metallic vanadium has an excellent hydrogen storage properties in comparison to other hydride forming metals such as titanium, uranium, and zirconium. The gravimetric storage capacity of vanadium is over 4 wt% which is even better than AB2 and AB5 alloys. The metallic vanadium has shown high hydrogen solubility and diffusivity at nominal temperature and pressure conditions. Consequently, vanadium is under consideration for the cost-effective hydrogen permeation membrane to replace palladium. The issues with vanadium are poor reversibility and pulverization. The poor reversibility is because of high thermal stability of β (VH/V2H) phase which eventually restricts the cyclic hydrogen storage capacity up to 2 wt% at room temperature. The pulverization is because of large crystal misfit between the metal and metal hydride phase. The hydrogen solubility, phase stability, hydrogenation-dehydrogenation kinetics, and pulverization are highly influenced by the presence of an alloying element. Therefore, worldwide efforts are to explore and optimize the alloying element which could enhance the hydrogen solubility, destabilized the β phase, improved the hydrogenation-dehydrogenation kinetics, and prevent the pulverization. The current review is a systematic presentation of these efforts to resolve the issues of vanadium as a base material for hydrogen storage and permeation membrane.

Abstracts Hydrogen production via thermochemical water-splitting by lithium redox reactions was investigated as energy conversion technique. The reaction system consists of three reactions, which are hydrogen generation by the reaction of lithium and lithium hydroxide, metal separation by thermolysis of lithium oxide, and oxygen generation by hydrolysis of lithium peroxide. The hydrogen generation reaction completed at 500 °C. The metal separation reaction is thermodynamically difficult because it requires about 3400 °C in equilibrium condition. However, it was indicated from experimental results that the reaction temperature was drastically reduced to 800 °C by using nonequilibrium technique. The hydrolysis reaction was exothermic reaction, and completed by heating up to 300 °C. Therefore, it was expected that the water-splitting by lithium redox reactions was possibly operated below 800 °C under nonequilibrium condition.

AbstractUnderstanding the lithiation–delithiation of the Mg–Li alloy during the absorption–desorption of hydrogen is essential for the development of Li‐ion batteries with MgH2 as a negative electrode. Tuning the hydrogenation–dehydrogenation kinetics and thermodynamics of the Mg–Li alloy could also be helpful to develop a lightweight material for on‐board hydrogen‐storage applications. Single‐phase Li3Mg7 (the highest % of lithium compound) was prepared by ball milling of LiH and MgH2 as precursors of Li and Mg followed by dehydrogenation at 400 °C under dynamic vacuum conditions. The cyclic hydrogenation–dehydrogenation behavior of the intermetallic was studied in detail. During hydrogenation, Li3Mg7 was delithiated to LiH and MgH2, whereas during dehydrogenation, LiH and MgH2 were lithiated to form the Li3Mg7 phase along with a Mg–Li solid solution. The hydrogenation–dehydrogenation kinetics of pristine Li3Mg7 were found to be slow. The hydrogenation–dehydrogenation kinetics were remarkably improved by doping with ZrCl4 as a catalyst. The activation energy and the thermodynamic parameters of the uncatalyzed and catalyzed alloy were evaluated, and the results were compared.

Abstract Thermochemical water-splitting by sodium redox reactions was investigated from material science point of view as a future hydrogen production method. The reaction system consists of three separate reactions, which are hydrogen generation by NaOH-Na reaction, metal separation by thermolysis of Na2O, and oxygen generation by hydrolysis of Na2O2. Although the current techniques of thermochemical water-splitting required a temperature higher than 800 °C for whole reaction cycle, the sodium system was able to be operated below only 400 °C by using nonequilibrium techniques to control the entropy of the chemical reactions. Therefore, this system should be recognized as a potential water-splitting technique that can widely utilize any heat sources in contrast to the conventional methods.