The search for less polluting and renewable energy sources that will replace fossil fuels, and consequently reduce CO2 emissions, has stimulated research into the development of a hydrogen-based energy system. Concerning hydrogen storage, several types of materials have been studied, such as hydrides (ionic, covalent or metallic), alanates (LiAlH4), starches (Mg (NH2)), and carbon and zeolite based materials. The metallic hydrides are presented as a safe and promising alternative for the storage of hydrogen in the solid state due to their superior gravimetric and volumetric capacities. Among the most investigated alloys for this application are the Mg alloys that despite having high storage capacity, present some disadvantages such as high temperatures and slow kinetics for hydrogen absorption/desorption. Different strategies have been used to improve hydrogen storage characteristics such as the preparation of nanocrystalline alloys and the addition of catalysts. Another strategy that aims to decrease desorption temperature has been the addition of alloying elements that will weaken the Mg-H bonds facilitating the hydrogenation and dehydrogenation. In addition to the cited factors, the alloy structure and number of interstices are important factors. Metal hydrides with body cubic centered (BCC) structures, which have a greater number of interstices per atom than the face centered cubes (FCC) and compact hexagonal (HC), and Laves phases have high storage capacity of hydrogen at room temperature. It has also been reported that lattice strain can also be favorable for hydride formation by acting as a driving force to open up new interstitial sites for hydrogen. In this context, the high entropy alloys (LAE) are presented as promising alternatives for application in hydrogen storage. High entropy alloys are multicomponent alloys in which the control of configurational mixing entropy and other parameters such as incompatibility of atomic size, enthalpy of mixing and electronegativity allow the formation of multicomponent solids solutions instead of intermetallic compounds. Lattice strain is a typical characteristic of high entropy alloys due to the variation in the atomic radii of constituent atoms. Recently, high entropy alloys with microstructures composed of solid solutions with BCC structure and Laves phase were investigated for hydrogen storage with promising results. The TiVZrNbHf alloy, which crystallizes as a single multicomponent solid solution, is capable of absorbing 2.5 hydrogen atoms per metal atom, which is considerably higher than conventional metal hydrides such as MgH 2. This project aims to develop LAE compositions with optimized hydrogen storage properties. The results obtained should contribute to a better understanding of the correlations between processing, structure and properties of high entropy alloys for hydrogen storage. This project is being carried out during an internship abroad, more precisely in the Science et Ingénierie des Matériaux et Procédés (SIMaP), laboratory of the Institut National Polytechnique de Grenoble, INP-Grenoble under the supervision of Dr. Yannick Champion. SIMAP has an excellent structure, especially in advanced materials characterization techniques, many of which will be essential for a complete understanding of the correlations between structure, microstructure and properties of the alloys to be developed. In addition to the expected scientific results, this project will be the start of establishing cooperative research relations between SIMAP and the Institute of Science and Technology (ICT) of UNIFESP.
News published in Agência FAPESP Newsletter about the scholarship: