Variations in the structural, optical and electrochemical properties of CeO2–TiO2 films as a function of TiO2 content

Alcohol based sols of cerium chloride (CeCl3 7H2O) and titanium propoxide (Ti(OPr)4) in ethanol mixed in different mole ratios have yielded mixed oxide films on densification at 500 8C. The reversibility of the intercalation/deintercalation reactions has shown electrochemical stability of the films. Addition of TiO2 in an equivalent mole ratio manifests in producing highly transparent films with appreciable ion storage capacity. The electrochemical studies have revealed the significant role of TiO2 in controlling the ion storage capacity of the films, as it tends to induce the disorder. In addition, the films prepared from an aged sol are observed to exhibit a much higher ion storage capacity than the films deposited using the as-prepared sol. The X-ray photoelectron spectroscopic studies have provided information on the variation of Ce4+/Ce3+ ratio as a function of increased TiO2 content in the films. This study has led to a better understanding of the increased ion storage capacity with the increased TiO2 proportion. The transmission electron microscopic study has demonstrated the presence of CeO2 nanograins even in films, which are amorphous to X-rays. Elucidation of the structural, optical and electrochemical features of the films has yielded information on aspects relevant to their usage in transmissive electrochromic devices. The films have been found to exhibit properties that can find application as counter electrode in electrochromic smart windows in which they are able to retain their transparency under charge insertion, high enough for practical uses. Also, the fastest coloration–bleaching kinetics for the primary electrochromic electrode (WO3) working in combination with Ce/Ti (1:1) electrode stimulates the use of latter in electrochromic windows (ECWs).