| Autor: |
Sytwu K; Department of Applied Physics , Stanford University , 348 Via Pueblo , Stanford , California 94305 , United States., Hayee F; Department of Electrical Engineering , Stanford University , 350 Serra Mall , Stanford , California 94305 , United States., Narayan TC; Department of Materials Science and Engineering , Stanford University , 496 Lomita Mall , Stanford , California 94305 , United States., Koh AL; Stanford Nano Shared Facilities , Stanford University , 476 Lomita Mall , Stanford , California 94305 , United States., Sinclair R; Department of Materials Science and Engineering , Stanford University , 496 Lomita Mall , Stanford , California 94305 , United States., Dionne JA; Department of Materials Science and Engineering , Stanford University , 496 Lomita Mall , Stanford , California 94305 , United States. |
| Abstrakt: |
Surface faceting in nanoparticles can profoundly impact the rate and selectivity of chemical transformations. However, the precise role of surface termination can be challenging to elucidate because many measurements are performed on ensembles of particles and do not have sufficient spatial resolution to observe reactions at the single and subparticle level. Here, we investigate solute intercalation in individual palladium hydride nanoparticles with distinct surface terminations. Using a combination of diffraction, electron energy loss spectroscopy, and dark-field contrast in an environmental transmission electron microscope (TEM), we compare the thermodynamics and directly visualize the kinetics of 40-70 nm {100}-terminated cubes and {111}-terminated octahedra with approximately 2 nm spatial resolution. Despite their distinct surface terminations, both particle morphologies nucleate the new phase at the tips of the particle. However, whereas the hydrogenated phase-front must rotate from [111] to [100] to propagate in cubes, the phase-front can propagate along the [100], [11̅0], and [111] directions in octahedra. Once the phase-front is established, the interface propagates linearly with time and is rate-limited by surface-to-subsurface diffusion and/or the atomic rearrangements needed to accommodate lattice strain. Following nucleation, both particle morphologies take approximately the same time to reach equilibrium, hydrogenating at similar pressures and without equilibrium phase coexistence. Our results highlight the importance of low-coordination number sites and strain, more so than surface faceting, in governing solute-driven reactions. |
