Crystallization of Mesoporous Metal Oxides

Kondo, Junko N.; Domen, Kazunari

doi:10.1021/cm702176m

Cited by 203 publications

(149 citation statements)

References 59 publications

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“…20 This can be attributed to the fact that nanocrystals grow at typical crystallisation temperatures to diameters of 10-20 nm, which by far exceed the length scales of the self-assembled P123 structure and therefore causing the micro-morphology to break down during annealing. Alternative concepts include backfilling the mesopores with carbon or silica 21 or elaborate annealing and crystallisation protocols 14 to enhance temperature stability or the addition of preformed TiO 2 nanocrystals to decrease the crystallisation temperature 22 but to simultaneously achieve high crystallinity and structural integrity remains a challenge. Furthermore phase impurities have repeatedly been reported with finite amounts of TiO 2 (B) and traces of rutile.…”

Section: Introductionmentioning

confidence: 99%

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO₂crystallisation

Guldin

Hüttner

Tiwana

et al. 2011

Energy Environ. Sci.

118

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Anatase TiO 2 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 TiO 2 crystallisation, preventing the collapse of porosity at temperatures up to 700 • C. The systematic study of the temperature dependence on DSC performance reveals a parameter trade-off: while high temperature annealed anatase consisted of larger crystallites and had a higher conductivity, 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.

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Section: Introductionmentioning

confidence: 99%

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO₂crystallisation

Guldin

Hüttner

Tiwana

et al. 2011

Energy Environ. Sci.

118

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“…This commonly observed phenomenon of collapse of the framework mesoporous transition metal oxides at high temperatures is believed to originate from nanocrystalgrowth-induced strain, which forces the mesopore network to self-destruct. [12] So what is special about meso-ATO? To try to understand what effects might contribute to its high thermal stability, a variable-temperature wide-angle X-ray scattering (WAXS) study with Rietveld refinement was performed on the doped and undoped forms of mesoporous tin dioxide.…”

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confidence: 99%

Dye‐Anchored Mesoporous Antimony‐Doped Tin Oxide Electrochemiluminescence Cell

et al. 2009

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Transparent conducting oxides (TCOs) represent a unique class of electrode materials whose hallmark is high electrical conductivity and high optical transparency in the visible spectral range. They are renowned as electrode materials in solar cells, organic light-emitting diodes, and flat-panel displays, on both rigid and flexible substrates. [1,2] A contemporary challenge in materials chemistry is to discover ways of increasing the surface area of TCOs while retaining their conductivity and transparency, a combination of properties that would, for example, enable a new platform for high-efficiency dye-immobilized electrochemiluminescence (ECL) displays, light-emitting diodes (LEDs), lasers, and (bio)chemical sensors.[3]Herein, we report the synthesis of mesoporous antimonydoped tin oxide films dubbed meso-ATOs, interesting candidates for a new type of electrode material that offers the unique combination of high-surface-area ordered mesoscale pores together with high electrical conductivity and high optical transparency, and further we show that it is capable of supporting chemically tethered ruthenium-based dyes, enabling it to function as an efficient and reusable solid-state ECL-based sensor.Why has it taken about two decades of research to achieve this sought after goal? One can trace the difficulty to a number of adverse contributing factors, one of which is the poor affinity between sol-gel precursors of conductive inorganic materials and the organic template-directing mesophase under the nonaqueous evaporation-induced self-assembly (EISA) conditions required to grow conducting mesoporous metal oxide films.[4] Another problem is that high conductivity is usually associated with high crystallinity, and for mesoporous transition metal oxide materials this necessitates crystallization of the as-synthesized amorphous metal oxide framework into a nanocrystalline version, which usually results in strain-induced collapse of channel and/or cavity walls of the mesopores. So far, only mesoporous tin-doped indium oxide (meso-ITO) materials have been reported, but either their conductivity is very low due to low crystallinity [5] or their conductivity is reasonable but the mesostructure can only be templated with a specialty polymer surfactant. [6]

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“…Highly crystalline structures offer unique advantages over amorphous architectures by providing a direct and rapid pathway for charge transport, thus decreasing the carrier-path length which in turn reduces recombination losses. [19,20] Various methods for the synthesis of crystalline TiO 2 architectures have been reported in the literature. Among the widely used processing routes to fabricate crystalline TiO 2 are hydrothermal, sol-gel, and calcination processes.…”

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confidence: 99%

A General Method for the Anodic Formation of Crystalline Metal Oxide Nanotube Arrays without the Use of Thermal Annealing

2008

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Valve metal oxides are versatile in their range of applications, which include high-K dielectrics, [1] gas sensing, [2] biomedical implants, [3,4] field emitters, [5] and photovoltaic cells. [6] It is now generally recognized that nanoscale control of metal oxide architectures permits significant enhancement of the properties utilized in the above applications. In particular, TiO 2 nanotube arrays formed by anodization [7] have demonstrated outstanding performance in gas sensing, [8] photocatalytic, [9] and photovoltaic applications. [10][11][12] Review papers on the subject are available. [13,14] To date, amorphous nanotube arrays have been synthesized by Ti anodization with an elevated-temperature heat treatment, with temperatures typically greater than 350 8C being required to induce crystallinity. [15] With regard to photoelectrochemical water splitting using thick-film Ti foil samples, [16][17][18] annealing at temperatures sufficient to induce crystallinity usually leads to the formation of a thick barrier layer, separating the nanotube-array film from the underlying metal substrate, where recombination losses can occur. This barrier layer acts to hinder electron transfer to the metal electrode (cathode) where water reduction takes place, in turn reducing the overall water-splitting efficiency. The need for high-temperature crystallization limits nanotube array use with temperaturesensitive materials, such as polymers, for applications such as photocatalytic membranes. Therefore, low-temperature synthetic routes, where a high-temperature annealing step for crystallization is not required, are needed to obtain the full benefit of this unique material architecture. Control of the nanotube-array crystallinity is also important for their application in dye-sensitized solar cells and photocatalysis, where charge-carrier transport improves with fewer grain boundaries. Highly crystalline structures offer unique advantages over amorphous architectures by providing a direct and rapid pathway for charge transport, thus decreasing the carrier-path length which in turn reduces recombination losses. [19,20] Various methods for the synthesis of crystalline TiO 2 architectures have been reported in the literature. Among the widely used processing routes to fabricate crystalline TiO 2 are hydrothermal, sol-gel, and calcination processes. However, crystallization by hydrothermal treatment leads to a strong reduction of the textural properties due to excessive coalescence of the inorganic framework, and structural damage results when hydrothermal treatment is performed on mesostructured TiO 2 .[21] With sol-gel synthesis, TiO 2 nanoparticles usually exhibit a high tendency to aggregate. [22] Similarly, with calcination the thus-generated TiO 2 crystals are usually too large to be accommodated within mesopore walls, resulting in structural collapse.[21]Herein we report a facile and novel method to fabricate crystalline TiO 2 nanotube arrays up to 1.4 mm in length at 80-120 8C, and their use in water photoelectrolysis and li...

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Crystallization of Mesoporous Metal Oxides

Cited by 203 publications

References 59 publications

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO₂crystallisation

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO₂crystallisation

Dye‐Anchored Mesoporous Antimony‐Doped Tin Oxide Electrochemiluminescence Cell

A General Method for the Anodic Formation of Crystalline Metal Oxide Nanotube Arrays without the Use of Thermal Annealing

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Crystallization of Mesoporous Metal Oxides

Cited by 203 publications

References 59 publications

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO2crystallisation

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO2crystallisation

Dye‐Anchored Mesoporous Antimony‐Doped Tin Oxide Electrochemiluminescence Cell

A General Method for the Anodic Formation of Crystalline Metal Oxide Nanotube Arrays without the Use of Thermal Annealing

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Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO₂crystallisation

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO₂crystallisation