Assorbimento di idrogeno in leghe ad alta entropia

The use of hydrogen as an energy carrier has been largely investigated in the past decades to help feeding the increasing energy demand of the human-kind, still dominated by fossil fuels consumption. Being an energy vector, hydrogen needs to be stored properly from production to consumption: solid storage is a promising solution since does not require high pressures as gaseous or liquid storage, being a much safer approach. In this work, attention is given to High Entropy Alloys (HEA) composed by a single body-centered cubic (BCC) solid solution, that are becoming materials of interest for the hydrogen-storage field, thanks to their unique properties. The high lattice distortion typical of concentrated solid solutions composed by at least five principal elements is believed to increase the hydrogen storage capacity of these materials. A HEA of composition TiVNbZrAl0.5 has been studied through empirical methods, to obtain a single BCC solid solution. The material was then synthesized and characterized, and its hydrogen storage properties has been investigated trough Differential Scanning Calorimetry (DSC) and volumetric methods. A rapid solidification technique through Planar Flow Casting (PFC) was performed, to evaluate the effects on the storage properties of the material. The alloy undergoes a partial transformation to an FCC hydride phase upon hydrogenation, and the process showed good cyclability and reversibility of the hydrogen absorption/desorption process. The maximum hydrogen storage capacity of 1.41 wt% (0.92 H/M) was measured in a Sievert apparatus and pressure-composition isotherms curves were collected at different temperatures, allowing to investigate the thermodynamics of the absorption process.