Rational Design of Nanosized Light Elements for Hydrogen Storage: Classes, Synthesis, Characterization, and Properties

Abstract

Hydrogen is often considered as a technology for the future owing to the limitations of current hydrogen storage materials in powering fuel cell vehicles. However, with the first hydrogen vehicles on the road and the need for better energy storage systems to back-up the increasing penetration of renewables, hydrogen based technologies will undoubtedly play an ever-increasing role in future energy schemes. To support the uptake of hydrogen, the challenge is to design better materials than This article is protected by copyright. All rights reserved. 2 the ones currently available. This means materials capable of reversible hydrogen uptake and release close to the ambient and with a storage capacity approaching 10 wt%. To date, materials with high hydrogen capacity are known but the lack of approaches to fully control the properties of these materials toward the targets for practical application still remains the drawback. In this context, the approach of particle size reduction or nanosizing has recently emerged as a potential mean to gain full control over the properties of high capacity hydride materials. This review aims to summarise current understanding toward the synthesis of nanomaterials and the potential of current knowledge to aid with the synthesis of nanosized hydrides with properties that could ultimately enable hydrogen storage at the ambient.

Controlling the Growth of LiBH4 Nanoparticles for Hydrogen Storage

“…To assess this aspect, the effects of typical functional head groups, i.e., –SH, –NH 2 , –COOH, R 4 N + , and R 4 P + (where R is an alkyl group) that have been shown to lead to significant changes in nanoparticle morphology were investigated. These surfactants also display hard/soft properties, and thus, their ability to bind more or less strongly to specific nanoparticles’ surface planes can also be assessed based on Pearson's hard and soft acid and base (HSAB) principle . According to this principle, the affinity between metal centers (Lewis acids) and coordinating ligands (Lewis bases) is stronger if they have similar hard or soft properties, i.e., hard acids prefer to bind to hard bases, and soft acids tend to bind to soft bases .…”

“…However, to date, the control of particle size remains a challenge for further research. Currently, a convenient method to achieve a “homogeneous” nanoparticle size distribution is performed through the confinement of borohydrides within the porosity of inorganic materials and in particular carbons . However, the difficulty of filling the pores, weight, and volume of the porous scaffold significantly impede the final hydrogen storage capacity of hydride/scaffold composite materials.…”

“…Typically, upon nanoconfinement in carbons, hydrogen storage capacity <20 % of the theoretical hydrogen storage capacity of the initial hydride has been reported, 15 and this is far from the practical requirement of capacities >5 mass% H 2 . An alternative method is through the synthesis of free‐standing and stabilized nanoparticles in a core–shell fashion as previously reported . In this work, a hydride core is encapsulated within a thin metallic shell that acts as a gateway for hydrogen uptake/release and protects the nanocore from extensive physical and chemical degradation.…”

“…However, to date, the synthesis of core–shell hydride structures is based on an empirical know‐how, which is not sufficient to fully control the potential of the approach. With a core–shell hydride, wet‐chemical methods are used for the preparation of the nanosized hydride cores . These methods include the solubilization of a hydride precursor in a solvent and its reprecipitation/recrystallization into specific particle morphologies.…”

“…In this context, stabilizing agents including surfactants are used to minimize the surface energy of nanoparticles (“naked” nanoparticles are not stable in solvents, both thermodynamically and kinetically, due to their high surface Gibbs energy). The use of surfactants can also facilitate the control of the morphology and size of nanomaterials during synthesis, because surfactants have been reported to influence the nucleation and growth process of nanoparticles and stabilize specific surface planes . Such an approach of solvent precipitation with surfactants has been proven to be very effective for the synthesis of various types of inorganic nanoparticles including catalysts and quantum dots .…”