Structure and formation mechanism of carbon-doped titanium oxide nanotubes

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Carbon-doped titanium oxide nanotubes are a promising material for several applications such as PEM fuel cells. The nanotubes have a high specific surface area, good electrical conductivity and, as first experiments showed, high oxidation stability.The tubes can be synthesized in alkaline solution via a hydrothermal process from titanium oxide. The oxide powder is transformed into multiwall nanotubes with typical inner diameters of 310 nm and a length up to 500 µm. An anatase-like structure or a titanate structure (H2Ti3O7) is suggested for the tubes. In connection with application, doping of as-produced tubes with various elements is reported in the literature including doping with carbon. The introduction of carbon is essential to achieve electrical conductivity. A common method for carbon doping is a temperature treatment in an acetylene/nitrogen gas flow. Application of this method on tubes leads to sintering and crystallization, however. As a result, only low amounts of tubes persist.To circumvent the disadvantages of thermal post processing, a new method was developed at TH Nürnberg. Instead of the tube material, the titanium oxide precursor powder is doped with carbon via carbothermal treatment. The tubes are synthesized in the hydrothermal process subsequently. The formation process of the tubes is discussed controversially up to now but of high interest for potential application. Therefore, the formation process will be investigated taking samples from the process after various time steps. The samples will be investigated regarding morphology, phase content and carbon incorporation. The information will be correlated with synthesis parameters like concentration of educts, pH value, temperature and duration.On the basis of the results regarding formation mechanism and carbon incorporation further optimization of the synthesis will be possible as a pre-requisite for application.