Abstract
The formation of palladium hydrides is a well-known phenomenon, observed for both bulk and nanosized samples. The kinetics of hydrogen adsorption/desorption strongly depends on the particle size and shape, as well as the type of support and/or coating of the particles. In addition, the structural properties of hydride phases and their distribution also depend on the particle size. In this work, we report on the in situ characterization of palladium nanocubes coated with HKUST-1 metal-organic framework (Pd@HKUST-1) during desorption of hydrogen by means of synchrotron-based time-resolved X-ray powder diffraction. A slower hydrogen desorption, compared to smaller sized Pd nanoparticles was observed. Rietveld refinement of the time-resolved data revealed the remarkable stability of the lattice parameters of α- and β-hydride phases of palladium during the α- to β- phase transition, denoting the behavior more similar to the bulk materials than nanoparticles. The stability in the crystal sizes for both α- and β-hydride phases during the phase transition indicates that no sub-domains are formed within a single particle during the phase transition.
Highlights
IntroductionThe hydrogen storage capacity and kinetics of hydrogen adsorption and desorption are strongly affected by the particle’s size and shape [2,3,4,5,6,7,8], which is an important parameter for catalytic applications [8,9,10,11,12,13,14]
Due to big difference in atomic number between Cu and Pd, the scanning electron microscopy images measured in secondary electron and high angle backscattered electron regimes evidence that the cubic particles correspond to palladium (Figure S5)
Smaller particles were reported to rich lower H/Pd values at the same temperature and hydrogen pressure [38], which means that their contribution to the total hydrogen adsorption is much smaller compared to bigger particles
Summary
The hydrogen storage capacity and kinetics of hydrogen adsorption and desorption are strongly affected by the particle’s size and shape [2,3,4,5,6,7,8], which is an important parameter for catalytic applications [8,9,10,11,12,13,14]. Bulk palladium materials exhibit a sharp phase transition from α- to β-hydride, resulting in a characteristic plateau in the pressure composition isotherm [1]. Different theoretical models were suggested as descriptive of the structure of palladium particles during formation and decomposition of hydrides [4,16,17,18,19]. The core-shell structures were suggested [18]
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