Thermodynamics of hydrogenation for Ti1−xZrxMnCr Laves phase alloys

The thermodynamics of hydrogenation for the Ti1−xZrxMnCr (x = 0, 0.1, 0.2, 0.32, 0.5, 0.7, 0.9, 1.0) alloys, which are characterized by the XRD Rietveld analysis as C14-type Laves phase, are evaluated by P–C isotherms measurements at different temperatures. Along with the increase of Zr content in the alloys, the pressure of the absorption/desorption plateau decreases monotonously; the average value of ǀΔHǀ increases linearly, and the average value of ǀΔSǀ decreases slightly; on the other hand, the hysteresis of hydrogenation reduces to a minimum at x = 0.32, and then rises again; the slope of the plateau increases first, then decreases, forming a maximum at x = 0.5. For the hydride formation of the Ti1−xZrxMnCr alloys, the values of ǀΔHǀ and ǀΔSǀ increase with the hydrogen concentration, except for that of the Ti0.8Zr0.2MnCr, where an opposite trend occurs, but all the ǀΔHǀ values in the Ti1−xZrxMnCr–H2 system are considerably lower than those in most Laves phase hydride systems. As combined effects of these trends, the Ti0.5Zr0.5MnCr alloy with the highest microstrain induced from the greatest mismatch of different atoms in the lattice, possesses the greatest plateau slope and the smallest variation width of ǀΔHǀ for the hydride formation; on the other hand, the Ti0.68Zr0.32MnCr alloy exhibits the best hydrogen storage properties, with a reversible hydrogen capacity of 216 ml/g, and good plateau characteristics.