X-ray diffraction and H-storage in ultrasmall palladium particles

Reduction in the grain size of a metal has been recognized to lead to significant differences in its hydrogen uptake characteristics. Specifically of interest are the more favorable kinetics and/or enhanced H-storage that may possibly occur in very small diameter metal nanoparticles. The structural transformations and weight percentage uptake isotherms of very small, carbon-protected Pd nanoparticles (nano-Pd) with average particle diameter ∼ 2-3 nm were studied. The nano-Pd data were compared to that from micron-size grained bulk-Pd. The correlation between the peaks in nano-Pd patterns with those in the bulk-Pd pattern concluded that both nano-Pd samples possess the same FCC structure as the bulk. There was no substantial difference in the lattice parameter between the bulk-Pd sample and the nano-Pd samples. Considerable differences were observed between the isotherm data of the bulk-Pd sample and the 3.1 nm nano-Pd sample. The bulk-Pd reference sample exhibited a flat plateau, characteristic of the coexistence of the α and β phases, and was in excellent agreement with the literature. Both samples investigated possessed smaller mean diameters and fewer atoms per particle than in previously mentioned work, yet both samples maintained an FCC structure and undergo the α to β phase transition. This is an abstract of a paper presented in the ACS Fuel Chemistry Meeting Fall 2005 (Washington, DC Fall 2005).