Hydrogen absorbing characteristics of nano-structured palladium via bulk mechanical alloying

Nano-structured functional materials are expected to have superior properties to the coarse-grained, bulk materials. In the present paper, pure palladium is refined to nano-sized state to investigate the hydrogen absorption and desorption behavior. Using the bulk mechanical alloying, the palladium platelets can be successfully refined to nano-sized grains with the order to 10 nm. In comparison of pressure composition isotherms between nano-sized and bulk palladium, the phase boundary of the Pd-H miscibility gap is significantly narrower for nano-Pd. While the hydrogen solubility at α/(α + β) phase boundary is much increased, that at β/(α + β) phase boundary is drastically reduced by nano-structuring. This might be because of the broadening of the site energy distribution, induced by the intrinsic strains constraining the nano-grains. The broadening mechanism of site energy distribution has direct influence on the hydrogen absorption and desorption processes. The Curie temperature for hydrogen adsorption and desorption is drastically reduced by 135 K through the nanostructuring. The above precise discussion helps us to make nanostructured material design in the hydrogen storage alloys and compounds.