Dresden 2009 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 1: Topical Session Nanoporous Functional Materials I
MM 1.3: Vortrag
Montag, 23. März 2009, 11:15–11:30, IFW A
Electrochemical actuation using nanoporous metals — •VISWANATH RAGHAVAN NADAR1, DOMINIK KRAMER1, and JÖRG WEISSMÜLLER1,2 — 1Forschungszentrum Karlsruhe, Institut für Nanotechnologie, Karlsruhe, Germany — 2Technische Physik, Universität des Saarlandes, Saarbrücken, Germany
Actuating in response to an electric stimulus is well known for solid insulators, for instance piezo-ferroelectrics and conducting polymers, where an electric field penetrating the sample creates bulk distortion. The more recent observation of reversible dimension changes in nanoporous metal electrodes exploits different physics: Varying the electrode potential results in the formation of double layer, with a local electric field that is screened in the surface region. Changes in the mean surface atom bonding, due to the excess charge, modify the capillary forces at the surface, and bulk strain is required to set up a compensating stress throughout the lattice. Owing to their large specific surface area and large capacity, nanoporous Pt, Au, Pd wetted by electrolytes will thus exhibit reversible volume changes when their potential is varied. In a suitable setup, the action can be seen with the naked eye. In-situ dilatometry studies on these metals demonstrate that the variation of reversible strain is a linear function with charge. This highlights the distinction of the underlying capillary parameter, the surface stress, from the surface tension. Outside of the double layer regime, the stress-charge response reflects, among other factors. Thus, experiments on actuation of nanoporous metals provide insights into the microscopic processes at the electrochemical interface.