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Abstract
With the global temperature rising due to the Greenhouse effect at the same time, the search for clean, efficient, renewable energy source is of utmost importance. Thermoelectric materials have been receiving attention due to their potential application in converting waste heat into electrical energy. Metal oxides has always been an important research focus in the field of thermoelectrics for their low production cost and availability. A series of phases exist in the Ti-O system that has higher electrical conductivity than TiO2 called the Magneli phases. These phases can be formed with simple reduction reaction, usually by carbon or hydrogen.
In this work, Magneli phase TiO2 was investigated for thermoelectric applications. TiO2-x pellets were made with the hydrogen reduction method and the carbon reduction method. XRD and TGA results were cross analysed to determine the exact phase and oxygen content of the sample pellets. The results show that reducing TiO2 have drastically increased its electrical conductivity by introducing free electrons, transforming the insulating TiO2 into a n-type semi-conductor. While lattice thermal conduction dominated, the thermal conductivity was not dependent on the oxygen content.
Magneli phase TiO2 was also fabricated with the carbon reduction technique. Graphite was embedded in pellets before being reduced at high temperature in an inert atmosphere. XRD analysis was done for phase characterization and to ensure no residual graphite was present. Electrical conductivity, Seebeck coefficient and thermal diffusivity measurements are done to estimate ZT.
Moreover, the electrochemistry property of Magneli phase TiO2 was investigated by employing the Linear Scanning Voltammetry for Hydrogen Evolution Reaction at various scanning rates. The polarization curves and Tafel plots were plotted.