Abstract
Hydrogen, with its high energy density, is considered a promising next-generation energy carrier as it has the potential to
be produced cleanly through electrolysis of water powered by renewable energy sources. However, efficient storage
poses a challenge due to hydrogen's poor volumetric energy density in gas or liquid phases. Solid-state storage using
metal hydrides, particularly from FeTi-based alloys, is seen as a solution due to their near-ambient operating conditions
and higher volumetric capacity while safer to handle. Hydrogenation of metal hydrides is fundamentally governed by their entropic and enthalpic properties, which combined determine the temperature and pressure conditions for hydrogenation. Therefore, compositional tuning through alloying is crucial for tailoring the thermodynamics of these materials for technological use. For this purpose, multicomponent thermodynamic modeling is regarded as a well-suited approach for guiding the development of these materials. From the computational thermodynamic aspect, while the widely accepted bcc order-disorder model has been
successfully employed in many systems, complexities arise when modeling AB metals and their hydrides, particularly
when A and B elements have vastly different hydrogen affinities. We recently addressed this problem by describing the metallic form of the FeTi-H system using an analytical derivation of the Gibbs free energy for the perfectly ordered state of the bcc order-disorder model [1]. This ensured the model was compatible with the metallic system, but how to extrapolate it to multicomponent alloys remained elusive. In this presentation, we propose a comprehensive framework for modeling the thermodynamics of FeTi-based
multicomponent AB-type interstitial hydrogen storage materials is proposed. The talk will focus on the requirement for
describing the paraequilibrium, a specific equilibrium state relevant to interstitial hydrogenation of alloys. In addition,
the model is simplified further by using Density Functional Theory (DFT) point-defect calculations to determine the site
preferences for substitutional impurities in the FeTi sublattices, which in turn allowed for targeting only the necessary
model parameters required to evaluate phase equilibria in the FeTi-based multicomponent system, paving the way for future FeTi-based multicomponent thermodynamic model assessments.
1 - E. Alvares, P. Jerabek, Y. Shang, A. Santhosh, C. Pistidda, T. W. Heo, B. Sundman, M. Dornheim, Modeling the
thermodynamics of the FeTi hydrogenation under para-equilibrium: An ab-initio and experimental study, Calphad 77 (2022) 102426. doi:10.1016/J.CALPHAD. 2022.102426.
