Abstract
Among compounds presenting reversible hydrogen storage properties at room temperature, FeTi-hydrides have recently re-attracted interest. These hydrides have good gravimetric and volumetric capacity and present relatively low-cost alternatives to other intermetallics. Due to its fast sorption kinetics and reversibility in mild conditions, this alloy is suitable for applications in hydrogen storage tanks and can serve as a medium to increase efficiency of a future clean energy economy. Moreover, these hydrides may have their thermo-kinetic properties tuned by partially substitution of Fe/Ti by other metallic elements. For this reason, developing multi-component thermodynamic models capable of describing the stability of these hydrides may support the development of novel alloys with optimal thermodynamic properties that satisfy technological requirements. In this regard, the CALPHAD method is a powerful tool to accurately calculate the thermodynamics of multicomponent systems. Therefore, metal-hydrides seem to be good candidates to benefit from computational thermodynamics in the design and the simulation stages. As an initial step in the modeling of a more complex FeTi-based family, the (FeTi) 1-xHx system was assessed employing the CALPHAD method through the use o OpenCalphad software. New thermodynamic data was acquired by measuring Pressure-Composition-Isotherm (PCI) curves and by calculating thermochemical properties through Density Functional Theory (DFT). The thermodynamic models of the phases were selected based on a critical analysis of literature information and ab initio investigation. Key thermodynamic properties such as dissociation pressure, formation enthalpies, and phase diagrams were calculated in good agreement with our newly acquired data as well as with those reported in the literature. The present work may serve as a ground for higher-order thermodynamic assessments as well as for kinetic models, helping the design of novel FeTi-based hydrides and their hydrogenation process simulation. It was the first time an unprecedented thermodynamic assessment was carried using OpenCalphad software.
