Effect of Substitution of Iron by Cobalt on Hydrogenation Properties of TiFe

The influence of the partial substitution of iron by cobalt in TiFe on the hydrogen absorption properties was systematically investigated. The pressure-composition isotherms were determined to establish differences in the thermodynamic properties. When cobalt was added to the classic TiFe compound the hydrogen storage capacity decreased markedly from TiFeH2 to TiFe0, 5Co0, 5 H1, 5 and the ? phase was not formed. The addition of cobalt as TiFe0, 5Co0, 5. has beneficial effects on the equilibrium plateaus of the hydrides: the plateaus become flatter and a significant reduction in the pressure hysteresis is observed. There is an ? phase (hydrogen insertion in a solid-solution): the corresponding first partie of the isotherms obeys to the Siervert law ( nH= P1/2). The values of ?H, ?S and hysteresis factor were obtained from plots of LnPe versus 1/T using the Van't Hoff relationship.