  FeTi-based hydrides have recently re-attracted attention as stationary
hydrogen storage materials due to favorable reversibility, good sorption
kinetics and relatively low costs compared to alternative intermetallic
hydrides. Employing the OpenCalphad software, the thermodynamics of the
(FeTi)$_{1-x}$H$_{x}$ (0 $\leq x \leq$ 1) system were assessed as a key basis
for modeling hydrogenation of FeTi-based alloys. New thermodynamic data were
acquired from our experimental pressure-composition-isotherm (PCI) curves, as
well as first-principles calculations utilizing density functional theory
(DFT). The thermodynamic phase models were carefully selected based on critical
analysis of literature information and \emph{ab-initio} investigations. Key
thermodynamic properties such as dissociation pressure, formation enthalpies
and phase diagrams were calculated in good agreement to our performed
experiments and literature-reported data. This work provides an initial
perspective, which can be extended to account for higher-order thermodynamic
assessments and subsequently enables the design of novel FeTi-based hydrides.
In addition, the assessed thermodynamic data can serve as key inputs for
kinetic models and hydride microstructure simulations.
