Electrochemical and spectroelectrochemical properties of SnO2 and SnO2/Mo transparent electrodes with high ion-storage capacity

Thin solid SnO2 and SnO2/Mo (10%, 2:1 and 1:1) films with an ion-storage capacity of 20 to 30 mC/cm(2) and weakly expressed cathodic electrochromism were deposited using the dip-coating technique. The films were deposited from peroxo sols prepared by reacting SnCl2 . 2H(2)O and a metallic molybclenum precursor with H2O2. Thermogravimetric, surface area [Brunauer, Emmett, and Teller (BET)], x-ray diffraction, and IR spectroscopic measurements of films heat-treated atl 500 degrees C (5 min) revealed a nanocrystalline (grain size similar to 30 Angstrom) cassiterite structure with a large surface area (similar to 60 to 70 m(2)/g). The electrochemical properties of the films were studied in a 1 M LiClO4/propylene carbonate electrolyte using cyclic voltammetry (CV) at different scanning rates (0.1 to 200 mV/s). Electrochromic properties, measured in situ with ultraviolet-visible measurements, revealed that the coloring/bleaching changes accompanying insertion/extraction of Li+ ion processes are 10 to 15% for SnO2/Mo (1:1) films but decrease to a few percent with decreasing Mo content. Low-scan-rate CV measurements confirmed the presence of two different redox processes: Sn4+/Sn2+ and Mo6+/Mo5+. This was confirmed from the ex:situ LR spectroelectrochemical measurements of films charged/discharged to different extents. IR spectra of films heat-treated at 500 degrees C in a vacuum also showed that SnO2/Mo (2:1) films contain Bronsted acidic protons. These films, because of their low coloration efficiency (2 to 10 cm(2)/C), are promising counterelectrodes for electrochromic devices with light reflection modulation.