The influence of polarization of titania nanotubes modified by a hybrid system made of a conducting polymer PEDOT and Prussian Blue redox network on the Raman spectroscopy response and photoelectrochemical properties

Highlights: • We focus on the influence of different polarization conditions onto the properties of composite. • Raman spectroscopy measurements were carried out to verify the crystal phase of materials. • At low and intermediate doping levels polarons populate the polymer chain. In this work we show the impact of applied potential on network vibrations and photoelectrochemical properties of a composite material containing hydrogenated titania nanotubes and poly (3,4-ethylenedioxythiophene) with iron hexacyanoferrate (H-TiO₂/pEDOT:Fehcf) acting as a redox centre. For this purpose, Raman spectroscopy measurements under the working electrode (WE) polarization were carried out, allowing investigation of changes in the structure of the obtained heterojunction. The photoelectrochemical behaviour of the H-TiO₂/pEDOT:Fehcf composite was also studied at different potentials of WE. Both, in-situ Raman spectroelectrochemical and transient photocurrent measurements were performed in aqueous 0.1 M K₂SO₄ electrolyte. The reduction and oxidation of the electrode material enabled control of the organic matrix doping level and in consequence processes occurring at the electrode/electrolyte interface. The intensity of bands typical for the organic part of the junction strongly depends on the applied potential: the highest intensity of Raman bands characteristic for the pEDOT chain was observed in the cathodic potential range, whereas under anodic polarization pEDOT signals diminish. On the contrary, the intensity and the positions of anatase active modes remain almost unchanged independently of the applied potential. Furthermore, the effect of various polarization conditions within the anodic and cathodic potential ranges on the photocurrents was also observed. The maximum value of the photocurrent is reached at +0.8 V vs. Ag/AgCl/0.1 M KCl and equals 290 μA/cm².