Thermodynamics of hydrogen absorption (desorption) in unoxidized and internally oxidized Pd–Ti alloys

Abstract

Hydrogen isotherms have been measured from 273 K to 323 K in solid solution, low Ti content fcc Pd–Ti alloys over H content ranges available up to pH2≈0.10 MPa. ΔHH and ΔSH have been determined from the H2 isotherms in the dilute phase region as a function of the H content of the alloys. Thermodynamic parameters have been determined for hydride formation and decomposition reactions from the temperature dependence of the plateau pressures. Hysteresis has been determined for the alloys up to Pd0.94Ti0.06; the Pd0.92Ti0.08 alloy does not form a hydride phase at T ≥ 273 K. Alloys were internally oxidized to form composites and the H2 solubilities re-determined. The isotherms indicate H trapping at the Pd/TiO2 interfaces. The enthalpies for H trapping have been determined by reaction calorimetry for the internally oxidized Pd0.98Ti0.02 alloy and the relative partial enthalpies for absorption are quite negative compared to H2 solution in the dilute phase of pure Pd. These results probe the properties of metal/oxide interfaces which are important for a number of technological applications.