Porous nanoparticle assemblies with enhanced properties for application in electrochemical thin film devices

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Titel: Porous nanoparticle assemblies with enhanced properties for application in electrochemical thin film devices
Autor(en): Klein, Jonas
Erstgutachter: Prof. Dr. Markus Haase
Zweitgutachter: Prof. Dr. Martin Steinhart
Zusammenfassung: Porous structures of functional nanoparticles have several properties that are beneficial for their potential applications in optical devices. Structures of this kind can be created in the form of nanoparticle thin films on electrically conductive substrates for electrochemical applications. Mesoporous layers of antimony doped tin dioxide (ATO, SnO2:Sb) nanoparticles, for example, can serve as an optically transparent scaffold, providing electrical conductivity over a broad potential range. Such conductive structures allow electrons to be transported to/from other electrochemically active materials located at the surface of the particles. In electrochromic devices, materials are used that change their optical behavior by oxidation/reduction. It is shown that layers composed of ATO particles with anchored viologen-based redox dyes exhibit remarkable switching times and good long-term stability. Both aspects are related to the rather unusual use of non-intercalating electrolytes, which can be used due to the intrinsic conductivity of ATO. In addition to the optically active layer, a charge storage layer is required in an electrochromic device to achieve high performance. For this purpose, ATO layers can be modified with cerium species that can be switched between +3 and +4 redox states. These layers offer high charge storage capacities with fast response times also in combination with non-intercalating electrolytes. In addition to nanoparticle layers that mainly provide electrical conductivity, the nanoparticles themselves can also have variable properties that depend on the redox state of the atoms in the particles. LaPO4:Ce,Tb nanoparticles can be mentioned as an example where the redox state of the cerium atoms influences the luminescence of the particles. Small amounts of Ce4+ quench the luminescence otherwise exhibited by the particles when the cerium atoms are in the +3 oxidation state. With the help of redox shuttles, the luminescence of non-conductive LaPO4:Ce,Tb nanoparticle layers can be reversibly switched with impressive switching times. The properties of porous structures of functional nanoparticles are, however, not only beneficial for optical devices but also for the synthesis of nanomaterials that show their properties only after calcination at high temperatures. One example is the n-type conductivity of ATO where the particle aggregates formed during calcination cannot be further processed into colloidal solutions. With respect to the latter, it is shown herein that nanoparticle aerogels are suitable for suppressing the formation of large aggregates of nanoparticles during the calcination process. In particular, by assembling aerogels from ATO (and titanium dioxide, TiO2) nanoparticles, colloidal solutions of these particles can be prepared even after calcination at 500 °C.
URL: https://doi.org/10.48693/341
Schlagworte: nanoparticles; electrochemistry
Erscheinungsdatum: 9-Jun-2023
Publikationstyp: Dissertation oder Habilitation [doctoralThesis]
Enthalten in den Sammlungen:FB05 - E-Dissertationen

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