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Electrochemical and Electrochromic Properties of Layer-by-Layer Films from TiO2 and Poly(vinyl Sulfonic Acid)

Fritz C. Huguenin ,  Nelson A. Galiote 

Universidade de Sao Paulo, FFCLRP, Departamento de Quimica (USP), Av. Bandeirantes, 3900, Ribeirao Preto 14040-901, Brazil

Abstract

Self-assembled electrodes formed from TiO2 nanoparticles and poly(vinyl sulfonic acid) (PVS) were prepared using the Layer-by-Layer (LbL) technique. The thickness of the 5-, 10-, 15-, and 20-bilayer films was 58 nm, 92 nm, 174 nm and 296 nm, respectively. The electrochemical and chromogenic properties of LbL films of TiO2/PVS have been examined in an electrolytic solution of 0,5 M LiClO4/propylene carbonate. It is noted the presence of two sites during the positive potential scan, which were attributed to ionic trapping effects. The absorbance change associated to oxidation of trapping TiO2 sites is attributed to electronic transitions involving energy states in gap band, which are formed due to strong distortion of the Li0.5TiO2 sites. Using the Quadratic Logistic Equation (QLE), it was possible to analyze the electronic transfer as a function of the number of lithium ions intercalated into the LbL film. From the parameters obtained from the fitting, it was also possible to determine the amount of trapping sites produced during the insertion of lithium ions. The electrochemical impedance spectroscopy (EIS) data show the presence of diffusion and trapping sites. The diffusion coefficient of lithium ions changed from 1.2x10-10 cm2.s-1 to 3.1x10-11­­ cm2.s-1 during the discharge process. Finally, the trapping effects associated to the amount of TiO2 nanoparticles are discussed.

 

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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium A, by Fritz C. Huguenin
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-12 20:30
Revised:   2009-06-07 00:44