Hydrogen isotope effect on thermodynamic and kinetic properties of Pd based ternary alloys: Pd–Ag-M (M = Au, Zr)

Abstract

Owing to the importance of hydrogen and its isotopes in energy sector, the present study investigates thermodynamic and kinetic hydrogen isotope effects on desorption reaction of newly synthesized Pd-based ternary alloy-hydrides/deuterides viz., Pd0.89Ag0.05M0.06 (M = Au, Zr)–H/D. Alloys were prepared by arc melting method followed by characterization using PXRD, SEM, TXRF and EDX techniques. The effect of hydrogen isotopes on thermodynamics of H2/D2 desorption reaction was investigated by generating pressure-temperature isotherms (PCIs) at various temperatures using a Sieverts' type volumetric apparatus. The PCT diagram of alloys depicts a single plateau which confirms desorption to be a one-step process. Both alloy systems display a normal isotope effect as indicated by higher plateau pressure for deuterides as compared to hydrides. The enthalpy and entropy changes for the desorption reactions were calculated using Van't Hoff equation. The separation factor derived from PCT data indicates that Pd0.89Ag0.05Au0.06 alloy has a significantly high separation factor as compared to other Pd based alloys reported in the literature. To get more insight into this behavior, non-isothermal kinetic analysis of H2/D2 desorption based on Differential Scanning Calorimeter (DSC) data acquired at four different heating rates was conducted and activation energies of desorption were calculated by invoking Kissinger's equation. The activation energies of alloys were found to be lower than that of palladium which explains the high separation factor of alloys as compared to Pd. The desired combination of higher separation factor and lower activation energy makes Pd0.89Ag0.05Au0.06 alloy a promising material for practical application in the separation of hydrogen isotopes via self-displacement gas chromatography (SDGC).