Spectroscopic Characterization of Nanocrystalline V/Ce Oxides for Novel Counter Electrodes

Abstract

The preparation of vanadium oxide and new mixed vanadium cerium (V/Ce) oxides thin films as intercalation compound for lithium ions started from aqueous inorganic precursors. Thin films of pure V and mixed (V/Ce) oxides at 78, 55, 38 and 32 at% of V were obtained via sol-gel process by dip-coated method which is a well known synthetic route for preparation of various oxide and mixed oxides materials. These films were prepared for counter electrode in electrochromic devices. All films were investigated by cyclic voltammetry CV, UV-VIS technique, FT-IR and Raman spectroscopy, atomic force microscopy (AFM), grazing-incidence X-ray reflectivity (GIXR), and grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide angle diffraction (GIWAXD). Improved electrochemical properties and cycling behaviour of vanadium oxide films were obtained after the addition of CeO₂. The intercalation of Li⁺ ions in V/Ce films was followed by FT-IR spectroscopy in combinations with CV measurements. The transmittance did not change significantly after cycling. The fundamental absorption edge shifts after the intercalation of Li⁺ ions. The best intercalation properties and cycling durability were obtained for films prepared at 55 and 38 at% of V. The amorphous grains between 50–100 nm were observed on the films surface at 55 at% of V, with AFM. No grain structure was observed at 38 at% of V but after the cycling increase the surface roughness and grain with grains size of 100 nm were observed. Layered structure in all V/Ce oxides was revealed by GIXR method.