Size and Shape Dependence of Hydrogen-Induced Phase Transformation and Sorption Hysteresis in Palladium Nanoparticles
arxiv(2024)
摘要
We establish a computational framework to explore the atomic configuration of
a metal-hydrogen (M-H) system when in equilibrium with a H environment. This
approach combines Diffusive Molecular Dynamics with an iteration strategy,
aiming to minimize the system's free energy and ensure uniform chemical
potential across the system that matches that of the H environment. Applying
this framework, we investigate H chemical potential-composition isotherms
during the hydrogenation and dehydrogenation of palladium nanoparticles,
ranging in size from 3.9 nm to 15.6 nm and featuring various shapes
including cube, rhombic dodecahedron, octahedron, and sphere. Our findings
reveal an abrupt phase transformation in all examined particles during both H
loading and unloading processes, accompanied by a distinct hysteresis gap
between absorption and desorption chemical potentials. Notably, as particle
size increases, absorption chemical potential rises while desorption chemical
potential declines, consequently widening the hysteresis gap across all shapes.
Regarding shape effects, we observe that, at a given size, cubic particles
exhibit the lowest absorption chemical potentials during H loading, whereas
octahedral particles demonstrate the highest. Moreover, octahedral particles
also exhibit the highest desorption chemical potentials during H unloading.
These size and shape effects are elucidated by statistics of atomic volumetric
strains resulting from specific facet orientations and inhomogeneous H
distributions. Prior to phase transformation in absorption, a H-rich surface
shell induces lattice expansion in the H-poor core, while before phase
transformation in desorption, surface stress promotes lattice compression in
the H-rich core. The magnitude of the volumetric strains correlates well with
the size and shape dependence, underlining their pivotal role in the observed
phenomena.
更多查看译文
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要