Paving the Way to the Fuel of the Future-Nanostructured Complex Hydrides

Hydrides have emerged as strong candidates for energy storage applications and their study has attracted wide interest in both the academic and industry sectors. With clear advantages due to the solid-state storage of hydrogen, hydrides and in particular complex hydrides have the ability to tackle environmental pollution by offering the alternative of a clean energy source: hydrogen. However, several drawbacks have detracted this material from going mainstream, and some of these shortcomings have been addressed by nanostructuring/nanoconfinement strategies. With the enhancement of thermodynamic and/or kinetic behavior, nanosized complex hydrides (borohydrides and alanates) have recently conquered new estate in the hydrogen storage field. The current review aims to present the most recent results, many of which illustrate the feasibility of using complex hydrides for the generation of molecular hydrogen in conditions suitable for vehicular and stationary applications. Nanostructuring strategies, either in the pristine or nanoconfined state, coupled with a proper catalyst and the choice of host material can potentially yield a robust nanocomposite to reliably produce H2 in a reversible manner. The key element to tackle for current and future research efforts remains the reproducible means to store H2, which will build up towards a viable hydrogen economy goal. The most recent trends and future prospects will be presented herein.

Effect of Different Amounts of TiF3 on the Reversible Hydrogen Storage Properties of 2LiBH4-Li3AlH6 Composite

Hydrogen is a potential green alternative to conventional energy carriers such as oil and coal. Compared with the storage of hydrogen in gaseous or liquid phases, the chemical storage of hydrogen in solid complex hydrides is safer and more effective. In this study, the complex hydride composite 2LiBH4-Li₃AlH₆ with different amounts of TiF₃ was prepared by simple ball-milling and its hydrogen storage properties were investigated. Temperature programmed desorption and differential scanning calorimetry were used to characterize the de/rehydrogenation performance, and X-ray diffraction and scanning electron microscopy (SEM) were used to explore the phase structure and surface topography of the materials. The dehydrogenation temperature decreased by 48°C in 2LiBH4-Li₃AlH₆ with 15 wt% TiF₃ composites compared to the composite without additives while the reaction kinetics was accelerated by 20%. In addition, the influence of hydrogen back pressure on the 2LiBH4-Li₃AlH₆ with 5 wt% TiF₃ composite was also investigated. The results show that hydrogen back pressure between 2.5 and 3.5 bar can improve the reversible performance of the composite to some extent. With a back pressure of 3.5 bar, the second dehydrogenation capacity increased to 4.6 wt% from the 3.3 wt% in the 2LiBH₄-Li₃AlH₆ composite without hydrogen back pressure. However, the dehydrogenation kinetics was hindered. About 150 h, which is 100 times the time required without back pressure, was needed to release 8.7 wt% of hydrogen at 3.5 bar hydrogen back pressure. The SEM results show that aluminum was aggregated after the second cycle of dehydrogenation at the hydrogen back pressure of 3 bar, resulting in the partial reversibility of the 5 wt% TiF₃-added 2LiBH4-Li3AlH₆ composite.

Tuning LiBH4 for Hydrogen Storage: Destabilization, Additive, and Nanoconfinement Approaches

Hydrogen technology has become essential to fulfill our mobile and stationary energy needs in a global low–carbon energy system. The non-renewability of fossil fuels and the increasing environmental problems caused by our fossil fuel–running economy have led to our efforts towards the application of hydrogen as an energy vector. However, the development of volumetric and gravimetric efficient hydrogen storage media is still to be addressed. LiBH₄ is one of the most interesting media to store hydrogen as a compound due to its large gravimetric (18.5 wt.%) and volumetric (121 kgH₂/m³) hydrogen densities. In this review, we focus on some of the main explored approaches to tune the thermodynamics and kinetics of LiBH₄: (I) LiBH₄ + MgH₂ destabilized system, (II) metal and metal hydride added LiBH₄, (III) destabilization of LiBH₄ by rare-earth metal hydrides, and (IV) the nanoconfinement of LiBH₄ and destabilized LiBH₄ hydride systems. Thorough discussions about the reaction pathways, destabilizing and catalytic effects of metals and metal hydrides, novel synthesis processes of rare earth destabilizing agents, and all the essential aspects of nanoconfinement are led.