Thermodynamics and kinetics hydrogen isotope effects of hydrogen/deuterium absorption in Pd-5wt.%Pt alloy

Abstract

Palladium–Platinum (Pd–Pt) alloys have excellent hydrogen isotope separation properties near room temperature compared to pure palladium (Pd), and are expected to be used as filling materials in thermal cyclic absorption (TCAP) columns. However, most studies on the thermodynamic and kinetic hydrogen isotope effects of hydrogen absorption/deuterium in Pd–Pt alloys have been conducted at temperatures of 273 K or above, with few studies involving the performance of TCAP in the cold-cycle operating temperature range (253 K–303 K). In this work, the performance of Pd-5wt.%Pt alloy for the absorption of hydrogen/deuterium at low temperatures (263 K–323 K) was investigated. The results show that the enthalpy and entropy of dissolution of hydrogen and deuterium in the α-phase of Pd-5wt.%Pt alloy are −11.77 kJ/mol (H), 104.00 J mol−1 K−1(H); −5.50 kJ/mol (D), 87.88 J mol−1 K−1 (D), respectively, which are lower than the enthalpy and entropy change values of pure Pd materials. The apparent reaction activation energies of protium and deuterium absorption are −4.14 kJ/mol (H2) and −11.87 kJ/mol (D2), respectively, which are lower than those of pure palladium. The excellent hydrogen isotope separation performance of Pd–Pt alloys may originate from the fast hydrogen absorption and discharge isotope kinetic performance.