Spectroelectrochemistry in the investigation of sol–gel electrochromic V2O5 films

Spectroelectrochemistry can offer important insights into the performance of materials that change properties during electrochemical treatment. The benefits of spectroelectrochemical measurements are shown through the example of an electrochromic sol–gel vanadium(V) oxide (V 2 O 5 ) film. In situ UV-visible absorbance spectroelectrochemistry is indispensable to reveal the optical modulation, which reached about 28% during the first coloration in the unsafe potential range, but then diminished to around 12% during the following cycles. Ex situ IR and Raman spectroscopy were used to probe the structural modifications that occur during the intercalation of small ions into the orthorhombic structure of the crystalline V 2 O 5 film. In particular, infrared reflection–absorption (IR RA) and IR absorption spectroelectrochemistry confirmed the red shift of the vanadyl band and the disappearance of the bridging oxygen band due to the puckering of layers of VO 5 square pyramids following intercalation. In addition, Raman spectra reveal the broad and low-intensity bands of the V 2 O 5 film after it has been coloured in the unsafe potential range. Electron energy-loss spectroscopy (EELS) revealed the presence of vanadium in oxidation states V 4+ , V 4+ /V 5+ , and V 5+ on different positions on the bleached film. Highlights Vibrational and UV-visible spectroelectrochemistry of sol–gel electrochromic V 2 O 5 films. In situ UV-visible absorbance of V 2 O 5 film defines its optical modulation. Ex situ IR reflection–absorption, IR absorption during coloration and bleaching. Ex situ Raman reveals significant band changes in the unsafe potential range. Ex situ EELS spectra confirm V 4+ , V 4+ /V 5+ , and V 5+ sites on the bleached film.