Hydriding properties of Ti-substituted non-stoichiometric AB2 alloys

Stoichiometric Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5 and non-stoichiometry (Ti0.1Zr0.9)1.1Mn0.9V0.1Fe0.5Co0.5, Ti0.1Zr0.9(Mn0.9V0.1)1.1Fe0.5Co0.5 and Ti0.1Zr0.9Mn0.9V0.1Fe0.55Co0.55 alloys have been synthesized and the lattice constants and unit cell volume have been obtained by using powder X-ray diffractograms. Pressure-composition (PC) isotherms have been obtained in the temperature and pressure ranges 30-125 deg. C and 0.1-30 bar using pressure reduction method and the effect of non-stoichiometry on the hydrogen absorption properties have been studied. Maximum hydrogen storage capacity is around 3.4 hydrogen atoms per formula unit at 30 bar and 30 deg. C in Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5. The relative partial molar enthalpy (ΔHH) and relative partial molar entropy (ΔSH) of the dissolved hydrogen have been calculated from the PC isotherms and their variation with hydrogen concentration has been plotted to identify the existence of different phases. The powder X-ray diffraction patterns of Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5-Hx (x=1.6 and 3.2) have been obtained in order to study the effect of hydrogenation on the crystal structure. The activation energy and diffusion coefficient of dissolved hydrogen in Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5 have been calculated from the kinetics of hydrogen absorption measurements at different temperatures and compared with Ti0.1Zr0.9Mn0.9V0.1Fe0.5Ni0.5. The effect of non-stoichiometry on the kinetics of hydrogen absorption at 50 deg. C has been studied and discussed