Hydrogen Isotope Effect on Thermodynamic and Kinetics of Hydrogen/Deuterium Absorption–Desorption in Pd_0.77Ag_0.10Cu_0.13Alloy

Abstract

The hydrogen isotope effect on the thermodynamic and kinetics of hydrogen/deuterium absorption–desorption in a single-phase ternary alloy Pd0.77Ag0.10Cu0.13 having fcc crystal structure was investigated using a Sievert-type volumetric apparatus to explore its viability for use in room-temperature self-displacement gas chromatography (SDGC) for separation of hydrogen isotopes. Desorption pressure–composition isotherms (PCIs) were measured in the temperature range 313–393 K, and the kinetics of the absorption reaction were studied using isochoric measurements in the temperature range 303–333 K. PCIs revealed that Peq(D2) > Peq(H2) at all experimental temperatures. Thermodynamic analysis of the biphasic region (α + β) reveals that |ΔrH°|(X=H) – |ΔrH°|(X=D) > 0 and |ΔrS°|(X=H) – |ΔrS°|(X=D) < 0. Analysis of kinetic data suggests that diffusion of X through the hydride/deuteride is the rate-limiting step. The combination of structural, thermodynamic, and kinetic data suggests that the Pd0.77Ag0.10Cu0.13–H2/D2 system has favorable properties for use in room-temperature SDGC for hydrogen isotope separation.