Directly grown TiO 2 nanotubes on carbon nanofibers for photoelectrochemical water splitting
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Directly grown TiO2 nanotubes on carbon nanofibers for photoelectrochemical water splitting Hyungkyu Han1, Stepan Kment1, Anandarup Goswami1, Ondrej Haderka1, Radek Zboril1* 1
Regional Centre of Advanced Technologies and Materials, Joint Laboratory of Optics and Department of Physical Chemistry, Faculty of Science, Palacky University, Slechtitelu 11, 783 71 Olomouc, Czech Republic ABSTRACT A variety of Titanium dioxide (TiO2) phases and nanostructures have been explored for their applications in photoelectrochemical cells (PECs) for solar-driven water splitting. In this case, anatase phase and TiO2 nanotubes offer significant advantages especially for PEC-based applications. Though, significant efforts have already been engaged to combine the advantages from both the fields, poor activation and the high electron-hole pair recombination rate of TiO2 electrodes, originating from intrinsic physicochemical properties, limits its practical use. As an alternative, we report directly grown TiO2 nanotubes (synthesized on Fluorine doped Tin Oxide (FTO) via facile electrospinning technique) on carbon nanofibers, using hydrothermal method. The hierarchical branch type configuration has an intimate contact between the TiO2 nanotube and carbon nanofiber backbone and offers higher photocatalytic activity than their respective individual components (namely TiO2 nanotubes and carbon nanostructures). INTRODUCTION Among the future sustainable energy alternatives, hydrogen (H2) has been considered as one of the most attractive sources mainly due to its clean production, cost-effectiveness, and high gravimetric energy density.[1] Considering the fact that hydrogen gas is currently produced mainly from variety of fossil fuels such as coal, tar sand, pitch, naphtha, and natural gas via steam methane reforming,[2] efficient production of hydrogen from sustainable and renewable method is required. In this respect, photoelectrochemical cells (PECs) which splits water directly upon illumination using semiconductor materials is a promising approach for direct conversion of renewable and sustainable sun light into large amount of hydrogen as a sustainable future energy carrier.[1-3] In this case, titanium dioxide (TiO2) semiconductor nanomaterials have attracted considerable attention as photoelectrode for solar driven water splitting due to its high natural abundance, nontoxicity, low cost, suitable band position, chemical stability in basic solution, and high resistance to photocorrosion.[4] In this respect, its worth mentioning that the anatase phase of TiO2 offers significant advantages including facile light confinement, efficient charge separation, high carrier mobility and hence is recommended for PEC based applications. Among the TiO2 nanostructures, TiO2 nanotubes has been proven to be beneficial for this purpose because of its high aspect and large surface-to-volume ratio, undirectional electrical channel, and efficient electron transport along the nanosized one-dimensional pathway.[5] Despite efforts to design anatase-based TiO2 na
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