Formation and stabilisation mechanisms of defects in carbon-doped and self-doped titanate nanotubes

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Titanate nanotubes (TNT), are a known type of inorganic, oxidic nanotubes, which can be doped with carbon to achieve C-TNT in order to alter the electric behaviour of the material. The synthesis procedure for C-TNTs described in the proposal ensures that a high specific surface area can be reached. The doped nanotubes thus meet the specifications for PEM fuel cell catalyst support such as high surface area and high electronic conductivity. However, the mechanisms behind the synthesis procedure and the origin of high conductivity are not clarified up to now. During the synthesis process, titanium oxide is treated in hot aqueous alkaline solution. After a certain process time, titanate nanotubes can be separated from the solution. The formation process of the tubes is still discussed controversially. A peeling scrolling mechanism is suggested as well as dissolution and precipitation. The synthesis and properties of the nanotubes is reproducible but further research work is necessary to understand the process and the material properties. The goal of the project is to provide further insight into the structure and structure formation of carbon-doped titanate nanotubes. Main questions are: How is carbon incorporated into the precursor powder and in the nanotubes? Is there any cooperative effect between titanium oxidation state, carbon and point defects in the structure? What changes in the structure are responsible for the enhanced electronic conductivity of the nanotube material? Results obtained could have impact on the further development of catalysts and catalyst supports, not only for fuel cell technology but also for catalysis and related processes in general.We assume that in reducing atmosphere during carbothermal treatment of the precursor powder Ti4+ species are reduced to Ti3+ and oxygen vacancies are formed and stabilised by carbon atoms. In our experimental approach, hydrogen is present due to the decomposition of acetylene during the carbothermal treatment of TiO2 powders at temperatures 700 – 800 °C, which should provoke Ti3+ species and oxygen vacancies.It is of great interest whether such defects can be transferred from C-TiO2 to C-TNTs during hydrothermal treatment in sodium hydroxide and how they affect the electrical properties of C-TNTs. The objective of the planned project is the investigation of C-doped titanium oxide nanotubes, with the goal to elucidate the location of the carbon in the structure and to clarify the formation mechanism with respect to the dopant and their influence on the C-TNT.