Sol–gel electrochromic WO₃ coatings on glass

Abstract

The structural study on precursor material of electrochromic (EC) tungsten oxide has been studied by differential thermal analysis (DTA), X-ray and FTIR. The electrochromic coatings having a thickness ∼300 nm were prepared by dipping technique. Out of the wide range of curing temperature (60–400 °C), the films cured at ∼200 °C for ∼1 h exhibited good electrochromic effect. Electrochromic properties of the tungsten oxide coatings were studied by cyclic voltammetry (CV), using a three-electrode cell system with 0.01 M HCl as an electrolyte. Cyclic voltamograms have been recorded ranging from −1.50 to 0.75 V at a scan rate range of 0.010–0.005 V s^-1. In aqueous medium, the coloration ↔ bleaching could not be continued more than five to eight cycles for acid to the corrosion of WO₃ films. If lithium-based nonaqueous electrolyte is used for this purpose, the coatings withstood more than 500 cycles. It is suggested that the films obtained after curing at requisite temperature for having the coloration ↔ bleaching effect contained mainly with the WOW bonding pattern in orthorhombic crystalline phase.