Inducing Porosity on Hollow Nanoparticles by Hypervelocity Impacts

Abstract

The large surface-to-volume ratio of hollow palladium nanoparticles (hNPs) offers room to improve their hydrogen storage capacity as well as their catalytic activity. However, a less explored possibility is to use, in addition, the internal cavity. Here we explore, through classical molecular dynamics, the possibility of boring channels across the hNP wall by collision with solid Pd nanoprojectiles at high velocities, as well as their resilience to maintain their spherical geometry. We choose a stable hNP with an inner diameter of 13 nm and an outer diameter of 15 nm. The projectiles are Pd NPs of 1.5, 2.4, and 3.0 nm, respectively. We consider collision speeds between 3 and 15 km/s, with an impact parameter between 0 to 7 nm. Four different regimes, as a function of kinetic energy and impact parameter of the projectile, are found. For low speeds, the projectile is not able to penetrate the target and only creates surface craters. For a narrow range of intermediate speeds, the projectile enters the target, but the hNP shell is able to self-heal, either totally or partially. For large speeds, the projectile penetrates the target without altering its spherical hollow geometry, but for even larger speeds, the hNP collapses into a solid structure. The specific threshold speed for each regime depends on the mass and speed of the projectile. In all noncollapsing cases, the results show a linear relationship between projectile kinetic energy and crater or perforation size. We also studied its behavior when the hNP suffers successive collisions, finding that it keeps its hollow shape but forms faceted structures, such as nanoframes or hollow cuboctahedron nanoparticles. All of our results suggest that Pd hNPs, with adequate combinations of external radius and thickness are very robust, can withstand hypervelocity impacts and that channels can be opened to allow molecules to reach the internal cavity.

Mechanical Properties Obtained by Indentation of Hollow Pd Nanoparticles

“…However, Shan et al proved that CdSe hNPs of about 500 nm can be subject to large stress without collapsing. Moreover, it was recently shown that hNPs of sizes no larger than 20 nm can withstand even hypervelocity impacts . In addition, several authors have suggested that hollow interior macroscopic spherical particles could be used as protective coating for space vehicles. − …”

“…Moreover, it was recently shown that hNPs of sizes no larger than 20 nm can withstand even hypervelocity impacts. 12 In addition, several authors have suggested that hollow interior macroscopic spherical particles could be used as protective coating for space vehicles. 13−15 Highly porous materials, such as aerogels, 16 nanofoams, 17,18 and bioinspired composites, 19 are also very attractive, since they display a combination of flexibility and toughness.…”

Understanding the Stability of Hollow Nanoparticles with Polycrystalline Shells

“…Each hNP, with a desired radius and thickness ( t ), was made by carving up a polycrystalline Au sample, with a specific average grain size ( d ), which is controlled through a Voronoi tessellation algorithm. , To avoid high energy grain boundaries or atom overlapping, we removed from the sample all the atoms with energies higher than 50 eV, principally from the grain boundary interface; then, we relaxed the polycrystal by using a conjugate gradient method coupled with a box relaxation algorithm. Also, to allow grain boundary re-accommodation, and to circumvent spurious effects due to high energy grain boundaries, we annealed the sample at a temperature of T = 2 T m /3, where T m is the Au melting point.…”

Spectroscopy of Palladium Nanoparticle Synthesis: Tailoring Nanoparticle Growth Parameters for Hydrogen Storage

“…Currently there is more of an emphasis on Pd hydride systems as it pertains to potential advances in the hydrogen economy [2]. In recent years, a wide variety of shapes [3][4][5] and sizes [6,7] have been studied for improved Pd hydride systems. As these complicated Pd nanostructures see more interest in the academic setting, industrial implications where quality and control of the size and structure of a potential product must be realized.…”