Berlin 2008 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 41: Poster SYM Hydrogen in Materials: New Developments
MM 41.15: Poster
Thursday, February 28, 2008, 18:00–20:00, Poster B
In-situ deformation study of porous nanocrystalline Pd during electrochemical charging — •Viswanath Raghavan Nadar1, Dominik Kramer1, and Jörg Weissmüller1,2 — 1Forschungszentrum Karlsruhe, Institut für Nanotechnologie, Karlsruhe, Germany — 2Technische Physik, Universität des Saarlandes, Saarbrücken, Germany
The length of porous nanocrystalline palladium in a nearly neutral aqueous NaF (0.7 M) electrolyte was measured using a commercial dilatometer as a function of the applied electrode potential and of the charge. As expected, the sample expands during formation of the palladium hydride phases. However, the length is not just a simple function of the faradaic charge, but shows a remarkable fine structure which we discuss using a comparison with other nanoporous samples, e.g. gold and platinum. Even without hydrogen ad- or absorption, the length of nanometals varies as a function of charge due to the variation of surface stress with charge density, which causes large variations of the bulk pressure of nanomaterials due to their large ratio of the number of surface atoms relative to the number of bulk atoms. The surface stress behaviour of palladium observed at potentials positive of the hydrogen adsorption is qualitatively similar to that of porous platinum, although there is a quantitative difference if one relates the expansion to the charge density, e.g. by calculating the surface stress-charge coefficient. The highly reproducible cyclic strain caused by hydrogen absorption and -desorption in Pd is larger than the surface stress effects by more than an order of magnitude.