Mention of nanotubes usually means carbon nanotubes. But not all tiny tubes
are made of carbon. For example, layers made of nanoscopic titanium dioxide
have proven to be useful materials for biotechnology, catalytic converters,
and solar cell technology. Although the semiconducting properties of these nanotubes
are critical for many of these applications, their limited conductivity represents
a hindrance for other areas of application. A team at the University of Erlangen-Nürnberg
and the University of Turku in Finland has now found an easy way to breathe
some metal-like conductivity into the nanotubes without changing their structure.
Through carbonization, the titanium dioxide can be converted into a carbon-containing
titanium oxycarbide compound. As the researchers led by Patrik Schmuki report
in the journal Angewandte
Chemie, this novel material could drastically increase the efficiency of
methanol fuel cells.
In order to carbonize titanium dioxide nanotubes, the researchers treated them
with acetylene at 850 °C. This forms a carbon-rich compound with semimetallic
properties, which is also significantly harder than before carbonization. “This
is not about simply doping titanium dioxide with carbon atoms,” clarifies
Schmuki. “Although the ordered tube structures remain almost completely
unchanged, a new chemical compound is formed. This titanium oxycarbide can be
interpreted as a solid mixture of titanium carbide and various titanium oxides.”
Its high electrical conductivity and favorable electrochemical characteristics
make this new material an interesting new electrode material.
Its use in methanol fuel cells seems particularly attractive. These days, methanol
oxidation is usually carried out at catalytic electrodes with a carbon support
and a platinum or ruthenium catalyst. “Titanium dioxide nanotubes have
been under consideration as an alternative to the carbon support for a number
of years,” says Schmuki. “But our new conducting oxycarbide beats
these by a mile: Supports made of the oxycarbide increase the activity of the
catalyst for the methanol oxidation by 700 %.”
Posted September 8th, 2009
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