Abstract:The pressure-composition (P-C) behavior of protium and deuterium in sponge Pd particle has been measured over a temperature range from 278 K to 323 K. Based on these data and combined with literature data, the effect of Pd crystal type and particle sizes on the thermodynamic properties in the Pd-H system was compared each other and discussed. The saturation solubility of hydrogen in solid solution region and the plateau pressure increase with decreasing Pd particle sizes at the ambient temperature. 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. The absolute value of phase transformation enthalpy and entropy from solid solution to hydride decrease with decreasing particle sizes 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 sponge Pd particle.