Environmentally Stable Hydrogen Storage by Thermal Shock Induced AB2 Alloy Nanoparticles in Reduced Graphene Oxide

Abstract

The growing threat of climate change warns us that the transition to a sustainable energy system is inevitable and urgent. However, despite the tremendous efforts from many governments and industries, the targets for zero CO2 emissions are falling short of the original plans. The bottleneck of the generalization of renewable energy is the demand for large-scale power storage facilities and grids based on the arbitrary power generation characteristic of renewable energy sources. A hydrogen-based energy system can compensate for these weaknesses through its high storage density and compatibility with the conventional gas pipeline. Nevertheless, hydrogen has to overcome the limitation of high cost for hydrogen purification and low volumetric storage capacity. Currently, hydrogen is stored in a gaseous form in which the density increase slows down as the pressure increases, reaching a limit value for volumetric storage density. In this respect, metal hydrides such as ABx alloys (TiMn2, LaNi5, TiFe, etc.) are an attractive storing option because they require much less space by storing hydrogen in metal lattices. Especially, AB2 alloys have relatively mild operation conditions with short (dis)charging time in contrast to other metal hydrides suffered from high desorption temperature and sluggish kinetics. However, an inert environment for application is still required for these alloys because of their vulnerability to impurity gases including O2, CO2, and H2O. Therefore, developing a complex material is important that can protect metal hydrides from other gases and alleviate their rigorous condition for handling. Here, we present reduced graphene oxide (rGO) coated Ti based AB2 alloy for environmentally stable hydrogen storage. The thermal shock method enables homogeneous nanosizing of alloy particles and a well-coated structure. Instantaneous heating and cooling interfere with phase separation and recrystallization to produce alloys of tens of nanometers on rGO. With its robust structure and excellent thermal conductivity, rGO not only prevents alloy particles from a potential contamination, but also facilitates heat dissipation, facilitating the hydrogen release process. Furthermore, nanosizing make alloy particles achieve faster hydrogen (dis)charging under milder conditions compare to their bulk counterparts. This post-treatment method through thermal shock can be applied to a variety of hydrogen storage metals for which nanoparticle formation has not been reported due to various compositions and limitations of pulverization methods, thereby contributing to the improvement of their durability and hydrogen storage properties.