What We Do?
Nanostructures
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Anodizing of valve metals and alloys is a powerful tool to control nanoscale architecture for transition metal oxides. One of the most promising systems is that formed on titanium, i.e. self-organized TiO2 nanotubes, because of unique semiconductive nature of titania applicable in photo-catalysis, light harvesting systems, electrochromic devices, batteries, matrices, templates, filtration membranes, and bio-compatible materials. Our research on nanotubes is focused on understanding of the growth process in view of formation of unique morphologies as well as synthesis of composites between titania and secondary materials, such as polymers, precious metals, metalloids, semiconductors, applicable in electrochemical energy storage devices. Our research is oriented on the synthesis step and key functional features in various fields of chemical engineering.
Self-healing materials
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The text below is a reprint published in
Chemical Science Vol. 2010 09 written
by Jon Watson RSC
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Steel is used to construct many different structures but is susceptible to corrosion, which can limit its practical uses and lifetime. Structures such as bridges or boats are often exposed to salt solutions that rapidly corrode them. This is a large problem and costs related to corrosion in developed countries amounts to approximately four per cent of their gross national product.
Damian Kowalski and coworkers at Hokkaido University have developed a new type of coating using an intrinsically conducting polymer (ICP), polypyrrole, which could be used as an alternative to expensive and toxic chromates currently used.
ICPs are, in effect 'synthetic metals', capable of conducting electrical currents or ions. Kowalski doped polypyrrole with heteropolyanions (PMoO3- and HPO2-). When the polymer coating is damaged, healing ions are released to the affected site, react with the steel forming an insoluble iron molybdate salt in the defect zone. This is different to other systems where usually a monomer is released to recreate the coating in the damaged region.
The key to the system is the control of the healing, explains Kowalski, 'in our work we have demonstrated how to control the release of these healing ions using an ion-permselectivity approach'. This stops the healing ions reacting with the metal before the coating is damaged, significantly increasing the lifetime of the coating.
Paul Braun, an expert in self-healing coatings at the University of Illinois, US, is impressed by the novel approach. Braun sees one possible advantage of Kowalski's system is its size, as it is 'much thinner than other coatings, which will be a distinct advantage for some applications'.
Kowalski is now developing the system to improve the healing response of the coating, attempting to reduce the size even further.
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Jon Watson
Lithium ion microbatteries
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Lithium ion batteries (LIBs) are one of the most important energy storage devices already commercialized for portable electronics in which the graphite anode with its charge storage capacity of 372 mA.h.g-1 is still utilized. To meet the demands of higher energy density in applications, such as electric vehicles, the present focus is on the anodes with high theoretical charge storage capacity. Silicon with its charge storage capacity of 3590 mA.h.g-1 corresponding to Li15Si4 formation may be a good negative electrode alternative. The main shortcoming of silicon in the form of micrometer in size particles and films is, however, its high volume expansion upon lithiation, resulting in high mechanical stress, pulverization and loss of electric contact leading to loss of charge capacity. A various approaches such as encapsulation and self-healing strategies are applied to overcome the shortcomings with high volume expansion. Our strategy related to electrochemical reduction of Si4+ to Si0 in ionic liquid electrolytes allows to form a robust silicon shell on titania nanotube wall. With its organized structure titania nanotube play a role of 1D current collector and serve a role of framework holding the nanostructured silicon upon lithiation/delithiation.
