Giant tuning on de/hydrogenation thermodynamics by constructing internal strain field in AB2 type hydrogen storage alloys

Abstract

Suitable dehydrogenation and hydrogenation (de/hydrogenation) thermodynamics, with enthalpy change (ΔH) in the range of 30–40 kJ/mol H₂, are necessary for operating hydrogen storage alloys (HSAs) at ambient temperature. Unfortunately, this is not satisfied in many HSAs, although many methods, such as alloying, nanosizing and constructing destabilization reactions, have been tried to tune the thermodynamics. In this work, controllable internal strain is induced in AB₂ type Y-Zr-Fe-Al alloys by careful control of dual-phase structure in which ZrFe₂ secondary phase with high de/hydrogenation equilibrium H₂ pressure (P_eq) can coherently precipitate in YFe₂ matrix phase with low P_eq. Thus, an internal strain field is constructed due to the interface mismatch and the asynchronous volumetric variation of the two phases during de/hydrogenation, and a giant change in de/hydrogenation thermodynamics is subsequently achieved. The dehydrogenation P_eq of the alloy with coherent dual-phase structure can be ∼166 times higher than that with single-phase structure, corresponding to a change of dehydrogenation ΔH from 63.7 kJ/mol H₂ to 44.8 kJ/mol H₂. Based on that, the contribution of internal strain is incorporated into the Van’t Hoff equation to determine de/hydrogenation P_eq by inducing a strain factor. The present work demonstrates that internal strain induced by designed precipitation, can vastly tune the de/hydrogenation thermodynamics and is of great significance for the application of HSAs.