Electrochemically Tunable Properties of Porous Nanophase Material
Eva-Maria Steyskal [1], Stefan Topolovec [1], Heinz Krenn [2], Stephan Landgraf [3], Roland Würschum [1]
15:00 - 17:00 Thursday 23 October 2014 Rechbauerstrasse 12, HSII Materials with tunable properties under an applied electric field are of great interest in many technology areas, ranging from basic research to industrial applications. For bulk materials, an observable property tuning is limited to nonmetals such as semiconductors or piezoceramics, owing to their low concentration of free charge carriers compared to bulk metals. In metals, due to effective screening, space charge regions are limited to a few atomic layers.
Porous nanophase materials open up a novel approach to property tuning due to their high surface-to-volume ratio. Immersed in an electrolyte, high excess charge densities as well as electrochemical surface reactions can reversibly be induced at the interface via potentiostatic control. In this contribution, two different approaches to prepare porous nanophase materials will be presented: On the one hand the compaction of nanocrystalline powders, allowing for a production of nanocomposites, where also insulating components can be charged indirectly via a conducting network. On the other hand the method of dealloying, where the less noble component is electrochemically dissolved from an alloy, resulting in a nanoporous network with extremely fine structures.
Case studies of tuning the magnetic and the electrical properties of porous nanophase materials will be presented. The first three-electrode electrochemical in-situ experiments in a SQUID magnetometer were performed, investigating the magnetic moment m of magehemite (γ-Fe2O3), which reveals two regions with a different magnitude of charge coefficient Δm/ΔQ, depending on the material’s oxidation state. The electrical resistance of nanoporous platinum, produced by dealloying of Cu75Pt25, is sensitively influenced by the presence of a strongly-bound, dealloying-induced superficial oxygen state and exhibits a sign inversion of the charge coefficient (ΔR/R0)/ΔQ, which will be discussed in this contribution.
|
