Thermodynamics of H2 Solution and Diffusion of H in (Pd0.77Ag0.23)1–xYx Alloys

Abstract

Hydrogen isotherms and thermodynamic properties have been determined for hydrogen solution in (Pd0.77Ag0.23)1–xYx alloys (x = 0.03 and 0.06). ΔHH and ΔSH have been determined as a function of r for 12H2 solution where r = H-to-(Pd0.77Ag0.23)1–xYx, molar ratio. The values of ΔHH° at infinite dilution of r are −24.5 and −29.6 kJ/mol H, for the (Pd0.77Ag0.23)0.97Y0.03 and (Pd0.77Ag0.23)0.94Y0.06 alloys, respectively, which are more exothermic than ΔHH° for solution of 12H2 in Pd0.77Ag0.23 or Pd. Diffusion parameters of H in the alloys have been determined from permeation measurements through (Pd0.77Ag0.23)1–xYx alloy membranes. The values of DH at infinite dilution of H, DH*, are 5.7× 10–6 and 2.5× 10–6 cm2/s for the (Pd0.77Ag0.23)0.97Y0.03 and (Pd0.77Ag0.23)0.94Y0.06 alloys, respectively (473 K), as compared to 8× 10–6 cm2/s for the Pd0.77Ag0.23 alloy. The permeation rates of H in the (Pd0.77Ag0.23)0.97Y0.03 and (Pd0.77Ag0.23)0.94Y0.06 alloy membranes are greater than that of the Pd0.77Ag0.23 membrane at 52...