High entropy alloys for hydrogen storage

Abstract

The search for cleaner and renewable energy sources that will replace fossil fuels has stimulated research into the development of a hydrogen-based energy system. Metal hydrides are a safe and promising alternative for solid state hydrogen storage due to their superior gravimetric and volumetric capacities. Different strategies have been used to improve hydrogen storage characteristics such as obtaining nanocrystalline alloys and the addition of catalysts. Catalysts lower the energy barrier for hydrogen dissociation, facilitating its absorption. Grain refining, in turn, increases surface area and grain boundary density favoring hydrogen diffusion and absorption/desorption processes. In addition to the factors mentioned, alloy structure and number of interstices are important factors. Metal hydrides with body-centered cubic structures, which have a greater number of interstices per atom, and Laves phases have shown high hydrogen storage capacity at room temperature. Lattice deformation may be favorable for hydride formation by acting as a driving force to make new interstitial hydrogen sites accessible. In this context, high entropy alloys (HEA) are promising alternatives for hydrogen storage applications. Lattice distortion is a typical feature of high entropy alloys due to variation in atomic radii of the constituent atoms. This project aims to develop HEA compositions with superior hydrogen storage properties, high storage capacity, fast hydrogen absorption/desorption kinetics at low temperatures and high resistance to environmental conditions. Alloys of different compositions will be studied within the TiVNbNiM (M = Co, Cr, Fe) system in which solid solutions with CCC structure and Laves phases in different proportions will be obtained. The alloys will be produced by mechanical alloying and the characterization of hydrogen properties will be performed by gas absorption (PCT) and electrochemical methods. The results obtained should contribute to a better understanding of the correlations between processing, structure and properties of high entropy alloys for this application. (AU)