Nanosize Effects on Hydrogen Storage in Palladium

Abstract

The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ( 0.4 and 7.0 ( 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the twophase state. By analyzing the isotherms, we quantitatively determined the heat of formation (∆H Rfβ ) and the entropy change (∆S Rfβ ) in the hydride formation of the nanoparticle. ∆H Rfβ and ∆S Rfβ for the 2.6 ( 0.4 nm diameter Pd nanoparticle were -34.6 ( 0.61 kJ(H 2 mol) -1 and -83.1 ( 1.8 J(H 2 mol) -1 K -1 , whereas for the 7.0 ( 0.9 nm diameter Pd nanoparticles the values were -31.0 ( 1.8 kJ(H 2 mol) -1 and -67.3 ( 5.1 J(H 2 mol) -1 K -1 , respectively. These quantities gave us a prospective picture of hydrogen absorption in Pd nanoparticles and the peculiarities in the formation of a single nanometer-sized hydride.

Preparation of Nanoporous Palladium by Dealloying: Anodic Polarization Behaviors of Pd-M (M=Fe, Co, Ni) Alloys

“…Among others, nanoporous palladium is a promising material for catalytic application, 12) hydrogen sensing 13) and hydrogen storage, 14) offering a large surface area. Typical and conventional nanoporous Pd is Pd black, which is composed of coagulated Pd nanoparticles having several hundred nanometer diameters.…”

Molecular Dynamics Study of the Particle Size Dependency of Structural Change in Hydrogenated Model f.c.c. Nanoparticles

“…Such positive dependency on particle size has been observed experimentally. 10,11) Numbers of hydrogen atoms coordinated by 4-6 metallic atoms are also shown in the figure. In cases of " 2, about 80% of the absorbed hydrogen atoms have six coordinating metallic atoms, which means that they locate mainly at O-sites.…”

“…Hydrogen absorption in nanoparticles has been studied for many years, mainly on Pd. [1][2][3][4][5][6][7][8][9][10][11] Pundt and coworkers 6,7) showed that the crystal structure of hydrogenated Pd nanoparticles varies depending on the cluster size. It includes not only the equilibrium and 0 phases in the f.c.c.…”

“…8) Behaviors of H atoms in lattice defects such as surface, interface, vacancy and dislocation have been pointed out as key issues in hydrogen storage. 9) Yamauchi et al 10,11) described cluster size dependent P-C isotherms of Pd nanoparticles in comparison with those in bulk samples. They reported that the large difference between nanoparticles and bulk resulted from surface effects.…”

Plasmonic gas and chemical sensing

“…Palladium constitutes an ideal model system for hydrogen dissociation and subsequent absorption processes in metals [56][57][58][59]. During catalytic loading, hydrogen molecules are first chemisorbed on the Pd surface, followed by near barrierless dissociation and subsequent diffusion of atomic hydrogen into the lattice.…”