Parameter Physics on Hydrogen Storage by Classical Molecular Dynamics Method

Abstract

Hydrogen storage in a model b.c.c. metallic nanoparticle was simulated by molecular dynamics method by changing length and energy parameters of metal-H bonds. A global image of hydrogen storage from the gas phase into the metallic nanoparticle was successfully reproduced by a single simulation. In case of weak metal-H bonds, hydrogen atoms rapidly diffuse into the particle and distribute homogeneously. The amount of absorbed hydrogen is maximized at optimized bond length, and decreases for both longer and shorter bonds. In case of strong metal-H bonds, hydrogen atoms localize in a shell-like layer near the particle surface and their inward diffusive motions are suppressed. Such a trapping phenomenon of hydrogen atoms near the surface is caused by low hydrogen diffusivity and lattice deformation due to the hydrogen absorption.

Simulation study of structural variation of metallic nanoparticles caused by hydrogenation

“…A computational model composed of isolated nanoparticles located at the center of cubic, periodic MD cells and surrounding hydrogen gas was considered [10]. The simulated particles were 10, 8, 6, 4, 2, 1.4, and 1 nm diameter; the corresponding numbers of E-mail address: ogawa@aist.go.jp metallic atoms vary from about 44 000 to 59 in b.c.c.…”

“…The number of hydrogen atoms is about 40 000. They were arranged initially in the face-centered cubic lattice with lattice constants of 0.3 nm within an octahedral space at the corner of the periodic cell [10]. After starting MD calculation, hydrogen atoms evaporate rapidly from the octahedral crystal because of the H-H repulsive forces.…”

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

“…They were arranged initially in the face-centered cubic lattice within an octahedral space at the corner of the MD cell. 12) After starting MD calculation, hydrogen atoms evaporate rapidly from the octahedral crystal because of the H-H repulsive forces and form a homogeneous gas phase outside the nanoparticles. The volume of the gaseous phase surrounding the nanoparticle varies about 15% according to the particle size.…”

“…The metal-hydrogen pair interaction, V M{H , is assumed to be variable by introducing two parameters as "V M{H ðr þ ÁrÞ for parameter physics, 12) where " and Ár respectively signify the energy and bond length parameters. As the reference function for V M{H , the potential function proposed by Ruda et al 17) for the Ni-H pair was adopted.…”

“…The present author recently conducted classical MD simulation on hydrogen absorption in metallic nanoparticles. [12][13][14][15] Previous studies have addressed the radial distribution of absorbed hydrogen atoms in nanoparticles, 12) grain boundary generation by hydrogenation, 13,14) and simulated P-C isotherms. 15) These studies were intended to elucidate mechanisms of hydrogen storage in nanoparticles on the concept of 'parameter physics' covering a wide phenomenological range.…”