NANOICP · Self-organized TiO2 nanotubes-intrinsically conductive polymer composite material for applications in solar cells, biomedicine systems, and electro-chromic devices

Self-organized TiO2 nanotubes-intrinsically conductive polymer composite material for applications in solar cells, biomedicine systems, and electro-chromic devices

Executive Summary: The NANOICP project aims to develop TiO2-nanotubes/conducting-polymer composite material by means of electrochemical deposition. The main objective is to combine an electric conductivity of the polymer and semiconductive nature of TiO2. The route for electrodeposition of the polymer inside TiO2 nanotubes has been fully achieved by using surfactant electrolyte of dodecyl sulfate and different current/potential protocols. Well defined nanostructures were obtained for polypyrrole (PPY) and Poly(3,4-ethylenedioxythiophene) (PEDOT). It has been established that the polymerization process can be controlled by modifications of the geometry of nanotubular titania framework in which the polymer is deposited inside the tubes and/or in free-space in between the tube walls. This leads to formation of specific polymer geometries on titania and well defined control over the contact area at the polymer/semiconductor interface. The deposition process critically depends on current/potential protocol. It was demonstrated that different polymer architectures are formed due to specific combination of high/low surface energy sites and nucleation/growth mechanism controlled by current/potential protocol. The size of the polymer was controlled within 10-150 nm depending on the deposition pathway and the size of titania template. The ability of polymer-titania to transfer an electric charge was studied by AC impedance spectroscopy; the charge transfer across the vertically aligned composite was controlled by the polymeric phase and therefore the composite is interesting in view of construction of solid state light harvesting systems. Another interesting feature, found within the project, is the use of TiO2 nanotubes as a template material for electrodeposited nanostructures. In principle, titania works similarly to a hard anodic aluminum oxide template (AAO) with the differences in geometrical structure of obtained nanostructures. It was demonstrated that current/potential Site selective electrodeposition in TiO2 nanotubes leads to formation of polymer nanowires or nanopore arrays if the polymer is deposited inside the tubes or in free-space between the tube walls, respectively. This electrodeposited nanopore array structure has many advantages over the classic nanowires (typically formed in AAO) in view of its mechanical properties, i.e. avoiding of agglomeration due to the surface tension forces and collapse of nanostructures arising from polymer flexibility. These new findings open the way for the formation of many well defined vertically aligned polymer nanostructures which should find applications in wide range of electrochemical systems.

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