Svetlana Korneychuk (Karlsruhe / DE), Stefan Wagner (Karlsruhe / DE), Georgian Melinte (Karlsruhe / DE), Rohleder Darius (Göttingen / DE), Philipp Vana (Göttingen / DE), Astrid Pundt (Karlsruhe / DE)
Abstract text (incl. figure legends and references)
Introduction
Palladium-based nanomaterials play an important role in hydrogen technology. Unique properties of Pd, such as high affinity to hydrogen, good solubility of up to H/Pd = 1 atomic ratio and fast hydrogen absorption and desorption at room temperature are very attractive for various applications. Besides catalysis, Pd nanoparticles can assist in hydrogen delivery into other materials for hydrogen storage. Pd-based materials are also used as hydrogen purification membranes and hydrogen detectors.
Objectives
The hydrogenation and dehydrogenation process of Pd nanoparticles is hence of high interest in the applications mentioned above. Nanoscale systems reveal significant thermodynamic deviations from the bulk due to higher surface to volume ratio, the absence of grain boundaries, and different behavior of defects. In this work we investigate the behavior of Pd nanoparticles and the formation of PdHx in real time with in-situ gas TEM at room temperatures and elevated temperatures which are required by many applications.
Materials & methods
The experiment was carried out at 80 kV on the ThermoFisher Scientific Themis Z equipped with Gatan GIF Continuum. In-situ hydrogen loading and unloading of Pd nanoparticles was accomplished with the gas system from Protochips. The sample was tightly sealed between two chips which both have electron transparent SiN windows, and analyzed at pressures of up to half atmosphere and temperatures of up to 200°C.
Results and Conclusions
We can observe the local phase change at different temperatures and pressures by measuring the position of the Pd bulk plasmon shift in low loss EELS [1]. With this technique we can study the direction of hydrogenation and dehydrogenation, hysteresis, size and shape related effects of the nanoparticles at various temperatures and pressures. In this work we also discuss the distinction of the quasi-planar surface plasmon modes in Pd nanoparticles from the PdHx signal.
Fig.1. EELS mapping of the Pd NPs at 140 °C and 13 kPa H2 showing the separation of Pd-H phases: solid solution (blue) and palladium hydride (orange).
[1] A. Baldi, et al, Nature Materials, 2014, DOI: 10.1038/NMAT4086