Relationship between Palladium Morphology and Thermodynamics in Palladium-Hydrogen System

Abstract

The pressure-composition (P-C) isotherms of protium and deuterium in Pd sponge particles have been measured over a temperature range from 278K to 323K. Based on these data and combined with literature data, the relationship between the Pd crystal type, particle size and thermodynamic properties in the Pd-H system was investigated. The saturation solubility of hydrogen in solid solution region ( a-phase) and the absorption plateau pressure increase with the decreasing Pd particle size at ambient temperature, but the desorption plateau pressure does not change with Pd morphology. The effect of Pd morphology on above two parameters gets weaker at higher temperature and the difference of plateau pressure among several different Pd morphologies disappears at higher temperature, such as 373K. The absolute value of phase transformation enthalpy and entropy from solid solution phase to hydride phase decrease with the decreasing particle size of Pd, but which are the smallest in single crystal Pd. The degree of hysteresis effect in Pd-H system depends on the background density in the sample, so it is the strongest in Pd sponge.