Detection of hydrogen absorption and desorption in individual palladium nano crystals

by Andrea Baldi (Department of Materials Science and Engineering, Stanford University (USA))

Wednesday 15 Jan 2014, 16:00 → 17:00 Europe/Rome

Dipartimento di Fisica - Ed. G. Marconi

Many energy and information storage processes rely on phase changes of nanostructured materials in reactive environments. Compared to their bulk counterparts, nanostructured materials exhibit faster charging/discharging kinetics, an extended life cycle, and size-tunable thermodynamics. Here, we present the first direct measurement of hydrogen absorption/desorption in individual palladium nanocrystals (size range: 13-29 nm), performed via in-situ electron energy-loss spectroscopy (EELS) in an environmenta! l (scanning) transmission electron microscope (E(S)TEM). We find that hydrogen intercalation in Pd nanocrystals is regulated by the coherent elastic coupling between the alpha and beta phases of PdH, resulting in an energy barrier that hinders thermal fluctuations and suppresses the coexistence of alpha and beta phases. Consequently, single-particle hydrogen loading/unloading isotherms are characterized by abrupt phase transitions and macroscopic hysteresis gaps. These findings are in striking contrast with ensemble measurements of Pd nanoparticles, in which sloped H2 loading/unloading isotherms suggested a thermally-driven nucleation of the hydride phase.