Ultrasmall Metal Oxide Nanoparticles for Energy Conversion and Storage
Dr. Dina Fattakhova-Rohlfing, Chemistry Department, LMU München
Metal oxides play an important role in photovoltaic and photoelectrochemical systems. Either as active materials, current collectors, barrier layers or as catalysts they are present in a vast amount of the currently explored devices. In our group we work on semiconducting functional nanostructured metal oxide materials, such as transparent conducting oxides with a periodic porous architecture and ultrasmall semiconducting metal oxide nanoparticles, for photovoltaic and photoelectrochemical applications. We develop new routes to the synthesis of metal oxide nanoparticles and the ways to their controlled assembly into continuous crystalline 3D-networks. We pay special attention to a full control over size, shape, composition, dispersibility, surface chemistry and the crystallinity of the nanoparticles.
Transparent conducting oxides (TCOs) are used as transparent current collectors in various photo(electro)chemical applications. TCOs have been known for a long time in the form of dense flat layers, but only recently the fabrication of 3D-conducting TCO networks has been reported. Transparent 3D-electrode architectures possess large interface area enabling incorporation of large amounts of functional guest species, electrical conductivity of the framework providing direct electronic access to the incorporated species, and optical transparency allowing interactions with light. We show fabrication of transparent conducting electrodes with various types and dimensions of 3D-nanostructures from different classes of TCOs, namely, antimony-doped tin oxide (ATO), niobium-doped titanium oxide (NTO) and indium tin oxide (ITO) by a directed self-assembly of corresponding nanoparticles [1-3].
We have extended the scope of the available metal oxide nanoparticles by introducing a novel non-aqueous protocol based on tert-butanol as a reaction medium. The particles prepared in this way are crystalline, non-agglomerated and dispersible in different solvents. Using this approach we have obtained crystalline dispersible nanoparticles of titania , electrically conducting Nb-doped titania , nickel oxide and cobalt oxide, whose size can be varied from ultra-small (2.5 nm) to relatively large (10 nm). The obtained nanoparticles demonstrate excellent properties in the application involving interfacial charge transfer and bulk charge transport processes such as dye-sensitized solar cells, and show promising properties as catalysts for electrochemical water splitting. Using this approach we have prepared the fastest ever reported titanate morphology for lithium insertion which can deliver up to 73 % of maximum capacity at unprecedented high rates 800 C (4.5 sec) . Currently we are working on the extension of our successful tert-butanol strategy for the fabrication of nanoparticles of other functional metal oxides and mixed oxides.
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