Influência do V2O5 nas propriedades eletroquímicas e morfológicas do filme de CeO2

Abstract

This work aims at a study of thin films of cerium oxide (CeO 2 ) and cerium oxide doped with vanadium pentoxide (CeO2:V 2O5 ), as well as its preparation and characterization, so they can be used as counter-electrode for electrochromic devices. The preparation was made by the sol-gel process. To obtain the sols, was used cerium chloride heptahydrate (CeCl3: 7H2O) and vanadium al koxide (OV(OCH(CH 3 ) 2 ) 3 - vanadium oxy isopropoxide) as precursors, ethanol as solvent and citric acid as catalyst. The films were deposited by spin coating on a conductive glass substrate (FTO). For the films have the desired electrochemical properties, a study was carried out previously. The characterizations was made via electrochemical techniques, as well as cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Morphological and structural studies of the films was made by scanning electron microscopy (SEM), X-ray diffraction measurements and atomic force microscopy (AFM). Studies on the processes of insertion / extraction of ions was performed by the spectroscopy in ultraviolet-visible (UV-Vis) technique. The best film was the one with concentration of V2O5 as dopant to the CeO 2 of 15 % mol and 5 layers of deposition. In the electrochemical analysis, the film did not show cathodic peaks, reaching a current intensity of 6 mA/cm² and storage capacity of ions of ~19 mC/cm² for polarization time of 60 seconds. The film showed good stability along the 200 cycles of intercalation/deintercalation. By the electrochemical impedance spectroscopy, it was proved that the intercalation occurs through a diffusional process. The morphological analysis showed a film with no cracks, no irregularity and homogeneous, with a rugosity of 9,42 nm and thickness of 300 nm. From the optical-electrochemical analysis, the film showed a decay of 4% on its transmittance values after the film polarization. Finally this film was evaluated as a counter-electrode in an electrochromic device.