Ordered mesoporous titania from highly amphiphilic block copolymers: tuned solution conditions enable highly ordered morphologies and ultra-large mesopores

Crystalline transition metal oxides with controlled mesopore architectures are in increasing demand to enhance the performance of energy conversion and storage devices. Solution based block copolymer self-assembly routes to achieve ordered mesoporous and crystalline titania have been studied for more than a decade, but have so far mostly been limited to water and alcohol dispersible polymers. This constraint has limited the accessible morphology space as well as structural dimensions. Moreover, synthetic approaches are mostly performed in a trial-and-error fashion using chemical intuition rather than being based on well-defined design parameters. We present solubility design guidelines that facilitate coassembly with highly amphiphilic block copolymers, enabling the formation of ordered structures with diverse length scales (d10 = 13.8–63.0 nm) and bulk-type morphologies. Thus, highly ordered and crystalline titania with the largest reported pores (d = 32.3 nm) was demonstrated for such a coassembly approach without the use of pore-expanders. Furthermore, the use of an ABC triblock terpolymer system led to a 3D ordered network morphology. In all cases, subsequent calcination treatments, such as the CASH procedure, enabled the formation of highly crystalline mesoporous materials while preserving the mesostructure

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO2 crystallisation

Anatase TiO2 is typically a central component in high performance dye-sensitised solar cells (DSCs). This study demonstrates the benefits of high temperature synthesised mesoporous titania for the performance of solid-state DSCs. In contrast to earlier methods, the high temperature stability of mesoporous titania is enabled by the self-assembly of the amphiphilic block copolymer polyisoprene-block-polyethylene oxide (PI-b -PEO) which compartmentalises TiO2 crystallisation, preventing the collapse of porosity at temperatures up to 700 degrees C. The systematic study of the temperature dependence on DSC performance reveals a parameter trade-off: high temperature annealed anatase consisted of larger crystallites and had a higher conductivity, but this came at the expense of a reduced specific surface area. While the reduction in specific surface areas was found to be detrimental for liquid-electrolyte DSC performance, solid-state DSCs benefitted from the increased anatase conductivity and exhibited a performance increase by a factor of three

HIGHLY CRYSTALLINE INVERSE OPAL TRANSITION METAL OXIDES VIA A COMBINED ASSEMBLY OF SOFT AND HARD CHEMISTRIES

A combined assembly of soft ansd hard chemistries is employed to generate highly crystalline three-dimensionality ordered macroporous (3DOM) niobia (Nb2O5) and titania (TiO2) structures by colloidal crystal templating. Polysterene spheres with sp(2) hybridized carbon are used in a reverse-template infiltration technique based on the aqueous liquid phase deposition of the metal oxide in the interstitial spaces of a colloidal assembly. Heating under inert atmospheres as high as 900 degrees C converts the polymer into study carbon that acts as a scaffold and keeps the macropores open while the oxides crystalize. Using X-ray diffraction it is demonstrate that for both oxides this approach leads to highly crystalline materials while heat treatments to lower temperatures commonly used for polymer colloidal templating, in particular for niobia, results in only weakly crystallized materials. Furthermore it is demonstrated that heat treatment directly to higher temperatures without generating the carbon scaffold leads to collapse of the macrostructure. The approach should in principle be applicable to othe 3DOM materials that require heat treatments to higher termperatures.X116268sciescopu

DIRECT ACCESS TO THERMALLY STABLE AND HIGHLY CRYSTALLINE MESOPOROUS TRANSITION-METAL OXIDES WITH UNIFORM PORES

Even after a decade or so of research, the direct synthesis of highly crystalline mesoporous transition-metal oxides that are thermally stable and well ordered still constitutes a major challenge. Although various soft-and hard-templating approaches have been developed in the past, they usually suffer from multiple, tedious steps and often result in poor structure control. For many applications including power generation and energy conversion, however, high crystallinity and controlled mesoporosity are a prerequisite. To this end, here we report on an approach established for group-IV (titanium) and group-V (niobium) oxides, with potential applications to photovoltaic cells and fuel cells, respectively, which overcomes previous limitations. It gives direct access to the desired materials in a 'one-pot' synthesis using block copolymers with an sp(2)-hybridized carbon-containing hydrophobic block as structure-directing agents which converts to a sturdy, amorphous carbon material under appropriate heating conditions. This in situ carbon is sufficient to act as a rigid support keeping the pores of the oxides intact while crystallizing at temperatures as high as 1,000 degrees C.X11411398sciescopu

Motion for a resolution tabled by Mr. Karl Heinz Mihr pursuant to Rule 47 of the Rules of Procedure on common policy in the telecommunications field. Working Documents 1981-1982, Document 1-246/82, 11 May 1982

The morphology of TiO2 plays an important role in the operation of solid-state dye-sensitized solar cells. By using polyisoprene-block- ethyleneoxide (PI-b-PEO) copolymers as structure directing agents for a sol-gel based synthesis of mesoporous TiO2, we demonstrate a strategy for the detailed control of the semiconductor morphology on the 10 nm length scale. The careful adjustment of polymer molecular weight and titania precursor content is used to systematically vary the material structure and its influence upon solar cell performance is investigated. Furthermore, the use of a partially sp 2 hybridized structure directing polymer enables the crystallization of porous TiO2 networks at high temperatures without pore collapse, improving its performance in solid-state dye-sensitized solar cells. © 2009 The Royal Society of Chemistry

Monolithic route to efficient dye-sensitized solar cells employing diblock copolymers for mesoporous TiO2

We present a material and device based study on the fabrication of mesoporous TiO2 and its integration into dye-sensitized solar cells. Poly(isoprene-block-ethyleneoxide) (PI-b-PEO) copolymers were used as structure directing agents for the sol–gel based synthesis of nanoporous monolithic TiO2 which was subsequently ground down to small particles and processed into a paste. The TiO2 synthesis and the formation of tens of micrometre thick films from the paste is a scalable approach for the manufacture of dye sensitised solar cells (DSCs). In this study, we followed the self-assembly of the material through the various processing stages of DSC manufacture. Since this approach enables high annealing temperatures while maintaining porosity, excellent crystallinity was achieved. Internal TiO2 structures ranging from the nanometre to micrometre scale combine a high internal surface area with the strong scattering of light, which results in high light absorption and an excellent full-sun power conversion efficiency of up to 6.4% in a robust, 3 μm thick dye-sensitized solar cell

BLOCK COPOLYMER DIRECTED SYNTHESIS OF MESOPOROUS TIO2 FOR DYE-SENSITIZED SOLAR CELLS

The morphology of TiO2 plays an important role in the operation of solid-state dye-sensitized solar cells. By using polyisoprene-block-ethyleneoxide (PI-b-PEO) copolymers as structure directing agents for a sol-gel based synthesis of mesoporous TiO2, we demonstrate a strategy for the detailed control of the semiconductor morphology on the 10 nm length scale. The careful adjustment of polymer molecular weight and titania precursor content is used to systematically vary the material structure and its influence upon solar cell performance is investigated. Furthermore, the use of a partially sp(2) hybridized structure directing polymer enables the crystallization of porous TiO2 networks at high temperatures without pore collapse, improving its performance in solid-state dye-sensitized solar cells.open118788sciescopu