In situ detection of hydrogen-induced phase transitions in individual palladium nanocrystals

Abstract

Many energy- and information-storage processes rely on phase changes of nanomaterials in reactive environments. Compared to their bulk counterparts, nanostructured materials seem to exhibit faster charging and discharging kinetics, extended life cycles, and size-tunable thermodynamics. However, in ensemble studies of these materials, it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, we detect the phase transitions of individual palladium nanocrystals during hydrogen absorption and desorption, using in situ electron energy-loss spectroscopy in an environmental transmission electron microscope. In contrast to ensemble measurements, we find that palladium nanocrystals undergo sharp transitions between the α and β phases, and that surface effects dictate the size dependence of the hydrogen absorption pressures. Our results provide a general framework for monitoring phase transitions in individual nanocrystals in a reactive environment and highlight the importance of single-particle approaches for the characterization of nanostructured materials.

The Hydrogen Grand Challenge

“…Apart from shortening the diffusion path lengths, nanostructured hydrides possess a higher surface area than pure hydrides, which improves the surface reaction kinetics. There have been reports that nanostructuring can change the stability of the hydride (Lohstroh et al, 2010;Baldi et al, 2014;Griessen et al, 2016) and even its decomposition reaction path (Mueller and Ceder, 2010). Both effects might originate from an increased contribution from the surface energy relative to the volume energy (Mueller and Ceder, 2010;Fichtner, 2011;Griessen et al, 2016).…”

“…Both effects might originate from an increased contribution from the surface energy relative to the volume energy (Mueller and Ceder, 2010;Fichtner, 2011;Griessen et al, 2016). It is telling that most of the research on hydrogen in nanoparticles relies on nanostructuring of palladium (Baldi et al, 2014;Griessen et al, 2016): Pd is a hydrogen absorbing, and chemically inert material, and nanostructuring recipes exist since long (Adams and Chen, 2011). The true challenge for materials science lies in finding and functionalization of non-precious metals with improved properties [e.g., as demonstrated by Lohstroh et al (2010), see also Figure 3].…”

Stress effects on the kinetics of hydrogen adsorption in a spherical particle: An analytical model

“…In the present case, however, concentration is prescribed in each phase because of (10). 8 In Cartesian components, (13) if the radius 9(t) of the a phase, and the velocity VðtÞ ¼ _ 9ðtÞ of the phase front are known, the boundary-value problems (14)e (15) can be solved explicitly to obtain the instantaneous values of the fields of interest in the bulk; an additional condition is needed in order to prescribe the motion of the interface.…”

“…Their analysis shows that transformation-induced strain makes it impossible for the two phases to coexist at equilibrium and, moreover, that it is responsible for the hysteresis loop observed in a cyclic adsorptionedesorption processes. Recently, these effects have been observed experimentally in individual Pd nanoparticles [8] and related studies have been conducted in Refs. [9] and [10].…”

Detection of water and its derivatives on individual nanoparticles using vibrational electron energy-loss spectroscopy

“…In spite of this outstanding spatial resolution, unambiguous, spectroscopic, local detection of water and OH species remains challenging with electronic excitation spectroscopy. The presence of hydrogen in solids must be inferred by careful analysis of near-edge fine structure or the valence-loss part of the spectrum without destroying the OH bond [23].…”