A calorimetric investigation of the thermodynamics of H2 absorption/desorption by Pd–Sn alloys

Abstract

Relative partial molar enthalpies, ΔHH, have been measured calorimetrically for the reaction of H2 with a series of disordered, fcc Pd–Sn alloys over the H content ranges available up to pH2≈0.17MPa at 303K. Enthalpy changes for the 12H2+dilute⇄hydride phase transition, ΔHplat, have been measured for both the hydride phase formation and decomposition. Hydrogen isotherms, pH21/2-r, have been determined (303K) for the Pd–Sn alloys where r=H-to-Pd1−xSnx, mol ratio. From the isotherms and ΔHH/T values, ΔSH has been determined as a function of r for the various alloys. At a constant low pH2, the H solubilities increase by alloying with Sn, however, they markedly decrease with increase of Sn at a constant, high pH2.