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

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 303 K. 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 (303 K) 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 pH2pH2, the H solubilities increase by alloying with Sn, however, they markedly decrease with increase of Sn at a constant, high pH2pH2.

► Calorimetrically measured partial enthalpies of H absorption by fcc Pd–Sn alloys (303 K).
► Enthalpies measured as a function of H content of the alloys.
► Partial entropies determined as a function of H content from equilibrium p and enthalpies.
► H capacities at 1 bar (303 K) p falls markedly with Sn content.