Electrochimica Acta 56 (2010) 737–744 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Light induced electropolymerization of poly(3,4-ethylenedioxythiophene) on niobium oxide F. Di Franco, P. Bocchetta, M. Santamaria ∗ , F. Di Quarto Dipartimento di Ingegneria chimica dei Processi e dei Materiali, Università degli Studi di Palermo, Viale delle Scienze, 90128 Palermo, Italy article info Article history: Received 20 July 2010 Received in revised form 11 September 2010 Accepted 18 September 2010 Available online 25 September 2010 Keywords: Niobium oxide PEDOT Photoelectrochemistry Band gap abstract The photoelectrochemical polymerization of poly(3,4-ethylenedioxythiophene), PEDOT, was successfully realized on anodic film grown to 50 V on magnetron sputtered niobium. Photocurrent Spectroscopy was employed to study the optical properties of Nb/Nb 2 O 5 /PEDOT/electrolyte interface in a large range of potential, and to get an estimate of the band gap and flat band potential of both the oxide and the polymer. Scanning Electron Microscopy was used to study the morphology of PEDOT. Both the optical and morphological features of the photoelectrochemically grown polymer were compared with those showed by PEDOT electropolymerized on gold conducting substrate. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction A conventional electrolytic capacitor consists of a valve metal (e.g. aluminium or tantalum), covered by an anodic film, the dielec- tric, in direct contact with an electrolyte, the true counter electrode, which in turn is connected to a current collector, usually made by the same valve metal. In the so called “solid state” tantalum elec- trolytic capacitors, the liquid electrolyte has been substituted by a solid ionic conductor (-MnO 2 ), whose conductivity is one of the drawbacks of the device. Thus, it has been recently proposed in the literature to replace manganese dioxide with a conductive polymer, which in principle can show a conductivity comparable to that of a metal [1]. Since 1999 [2], poly(3,4-ethylenedioxythiophene) has been suc- cessfully proposed as suitable conducting polymer for tantalum solid capacitor due to its excellent environmental stability. Usually, PEDOT is synthesized chemically in aqueous medium in the pres- ence of an oxidizer agent (i.e. ferric sulphate). However, this method can leave strongly acidic oxidant on the polymer chains, which can cause the degradation of the dielectric, thus the electropoly- merization should be safer for preparing PEDOT to be employed as counter electrode in solid state capacitors [3]. To overcome the dif- ficulty of performing such electrochemical process on dielectrics, we recently proposed a photoelectrochemical method [4] to grow polypyrrole on tantalum oxide. Such method has been successfully ∗ Corresponding author. E-mail address: santamaria@dicpm.unipa.it (M. Santamaria). employed to synthesize PEDOT on Ta 2 O 5 [3] and on Ti–Zr mixed oxides [5]. Few examples of photoelectrochemical polymerization on semi- conductors have been reported in the literature for protection against corrosion of the materials [6] or as reaction initiators [7]. On the other hand, high cost and limited availability of tantalum natural resources are pushing capacitor technologists to replace Ta with Nb, which is more abundant in earth crust and whose oxide, i.e. Nb 2 O 5 , has a permittivity higher than that measured for Ta 2 O 5 . However, as far as we know, only a paper has been published reporting on the chemical polymerization of pyrrole and aniline on Nb 2 O 5 to be employed in electrolytic capacitors [8]. In this work we report on the photoelectrochemical polymeriza- tion of PEDOT on anodic film grown to 50 V on magnetron sputtered niobium. Photocurrent Spectroscopy was employed to study the optical properties of Nb/Nb 2 O 5 /PEDOT/electrolyte interface in a large range of potential, while Scanning Electron Microscopy was used to get information of the morphology of the polymers. The characteristic features of the photoelectrochemically grown polymer were also compared with those showed by PEDOT elec- tropolymerized on gold conducting substrate. 2. Experimental The electropolymerization was performed on gold electrode (rod 4 mm diameter or foils) in 0.1 M LiClO 4 propylene carbonate (PC, 99.8 Sigma–Aldrich) with 0.1 M 3,4-ethylenedioxythiophene (EDOT). 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.09.062