Ex situ and in situ infrared spectroelectrochemical investigations of V2O5 crystalline films

Vanadium oxide (V2O5) films were prepared by dip-coating from V-oxoisopropoxide sols and heating at 300 degrees C for 1 h. Transmission electron microscopy combined with small area electron and X-ray diffraction revealed that the films consist of disordered V2O5 grains with an orthorombic structure (P-mmm). Electromotor force (emf), cyclic voltammetric (CV), and chronocoulometric measurements, combined with in situ ultraviolet-visible (UV-vis) spectroelectrochemical measurements, revealed similar electrochromic and electrochemical properties with other sputtered and sol-gel derived V2O5 films. IR absorbance and reflection-absorption spectra, performed at near-grazing incidence angle (NGIA) conditions (80 degrees, P-polarized), allowed us to compare the observed transverse optical (TO) and longitudinal optical (LO) frequencies of films with the TO and LO mode frequencies obtained from the dispersion analyses of V2O5 crystalline reflection IR spectra. TO and LO spectra of charged films show that Li+...O interactions modify the terminal V-OA (vanadyl), bridging V-O-B-V, and edge-sharing V-O-C stretching frequencies, suggesting that these interactions take place between the oxygens bordering the cavities in which Li+ ions are accommodated during charging. The red-frequency shift of the V-O-A stretchings [1016 cm(-1) (TO), 1035 cm(-1) (LO)] and the disappearance of the bridging V-OB-V stretching mode [795 cm(-1) (TO), 895 cm(-1) (LO)] can be used as a diagnostic tool to differentiate between films cycled in the safe and unsafe potential regions. A polaron absorption was observed above 2000 cm(-1) in the ex situ TO and in situ NGIA reflection-absorption (LO) spectra of films charged in the safe potential region. (C) 1999 The Electrochemical Society. S0013-4651(98)05-028-9. All rights reserved.