Photo-assisted electrodeposition of an electrochemically active polypyrrole layer on anatase type titanium dioxide nanotube arrays

Abstract

Our purpose is here to produce a large area 3D junction between anatase type TiO2 and polypyrrole (PPy) in a Ti/TiO2 nanotube array (NTA)/PPy assembly with the help of electrochemical methods only. We report herein the influence of light and background salt on the electrochemical polymerization of pyrrole from aqueous electrolytic solutions on titanium oxide NTAs, a well-known large specific area n-type semiconductor substrate. As titanium dioxide is known to be poorly conducting in the anodic potential range, we confirmed that light is able to initiate a polymerization process of pyrrole, at a moderately high anodic potential. For comparison with results obtained in sodium dodecylbenzenesulfonate (SDBS) at micellar concentration, we used here also lithium perchlorate as background salt at a 0.1M concentration, and PPy growth was found to be faster in the presence of LiClO4. Moreover in the latter case polypyrrole could be initiated in the dark as well, yet at an enhanced deposition rate under UV light. In the two solutions. the resulting polypyrrole films were found to be electroactive, i.e. able to undergo electrochemically driven doping/undoping processes, yet with a higher electroactivity for the film obtained in LiClO4. SEM-FEG and Raman spectroscopy experiments confirmed respectively that i) the initial steps of the photo-assisted electrodeposition of polypyrrole films occur first at the mouth of the titanium dioxide nanotubes, before leading to the well-known cauliflower-like morphology for PPy and ii) PPy is systematically produced in a doped state.