Hydrogen absorption of nanocrystalline palladium

Thermodynamic properties of hydrogen in nanocrystalline Pd (Pd-n) were determined by pressure-composition (P-C) isotherms. Pd-n was prepared by repeated compression-extrusion cycles in the die cavity of a high speed forging apparatus. It was found that Pd obtained was composed of nano-sized Pd grains, i.e. ∼10 nm, which were strained in 〈111〉 and 〈100〉 by 1.3 and 2.4%, respectively. From P-C isotherm measurements over the temperatures from 298 to 373 K, it was found that the hydrogen solubility in the α phase region for Pd-n was significantly larger than that for coarser grained Pd. On the other hand, Pd-n showed lower plateau pressures than coarser grained Pd. In addition to the above, the maximum hydrogen solubility of Pd-n was almost 50% lower than that for coarser grained Pd. The differences in the hydrogen solubility and plateau pressure between Pd-n and coarser grained Pd will be discussed under the consideration of the structure of nano-sized Pd grains. The drastic reduction in the maximum hydrogen solubility for Pd-n could be related to the viewpoint of strain of the octahedron in f.c.c. Pd.