Fundamental hydrogen storage properties of TiFe-alloy with partial substitution of Fe by Ti and Mn

TL;DR

This study explores how partial substitution of Fe with Ti and Mn in TiFe alloys affects their hydrogen storage properties, revealing enhanced capacities and altered thermodynamics suitable for large-scale applications.

Contribution

It provides a comprehensive analysis of thermodynamic and hydrogenation properties across a range of Ti and Mn substitutions in TiFe alloys, highlighting the effects on storage capacity and hysteresis.

Findings

Ti-rich alloys show increased storage capacities.

Mn and Ti substitutions lower plateau pressures and hysteresis.

Thermodynamic data align with existing literature, expanding understanding.

Abstract

TiFe intermetallic compound has been extensively studied, owing to its low cost, good volumetric hydrogen density, and easy tailoring of hydrogenation thermodynamics by elemental substitution. All these positive aspects make this material promising for large-scale applications of solid-state hydrogen storage. On the other hand, activation and kinetic issues should be amended and the role of elemental substitution should be further understood. This work investigates the thermodynamic changes induced by the variation of Ti content along the homogeneity range of the TiFe phase (Ti:Fe ratio from 1:1 to 1:0.9) and of the substitution of Mn for Fe between 0 and 5 at.%. In all considered alloys, the major phase is TiFe-type together with minor amounts of TiFe2 or \b{eta}-Ti-type and Ti4Fe2O-type at the Ti-poor and rich side of the TiFe phase domain, respectively. Thermodynamic data agree with the available literature but offer here a comprehensive picture of hydrogenation properties over an extended Ti and Mn compositional range. Moreover, it is demonstrated that Ti-rich alloys display enhanced storage capacities, as long as a limited amount of \b{eta}-Ti is formed. Both Mn and Ti substitutions increase the cell parameter by possibly substituting Fe, lowering the plateau pressures and decreasing the hysteresis of the isotherms. A full picture of the dependence of hydrogen storage properties as a function of the composition will be discussed, together with some observed correlations.