An overview and experimental analysis of WO₃/TiO₂ composite with enhanced electrochromic properties for smart windows application

Internationally, standards for electrochromic (EC) requirements in smart window applications have been established, with ongoing global initiatives aimed at elevating them to highly advanced levels. This paper covers a comprehensive investigation of the structural, optical, morphological, and electrochemical properties of WO3/TiO2 composite films. Simultaneously, an experimental analysis of WO3/TiO2 was envisaged by a two-step process. Initially, WO3 thin films were hydrothermally deposited onto indium-doped tin oxide-coated glass substrates using an aqueous solution of Na2WO42H(2)O at a pH value of 1. Subsequently, a layer of TiO2 was electrodeposited onto the WO3 thin films. X-ray diffraction analysis confirmed the successful formation of WO3/TiO2 composite films, with the WO3 phase exhibiting a hexagonal tunnel structure. Scanning electron microscopy revealed the formation of porous nanorods (NRs) of WO3, uniformly coated with TiO2, resulting in a porous morphology of the WO3/TiO2 samples. The EC performance of the WO3/TiO2 films was thoroughly assessed through cyclic voltammetry and chronoamperometry measurements over a potential window ranging from - 2.0 to + 1.2 V (versus Ag/AgCl) in a 0.5 molL-1 LiClO4-PC electrolyte. The WO3/TiO2 composite films exhibited cathodic electrochromism, characterized by a reversible color change from dark blue to transparent. This improved EC performance in comparison to pure WO3 films is attributed to enhanced double ion/electron insertion and extraction efficiency. Furthermore, the WO3/TiO2 composite films demonstrated excellent optical modulation properties, with a significant modulation at 633 nm (46.87%). The coloration efficiency reached a high value of 193.25 cm(2)C-1, indicating their potential for practical EC applications. Moreover, the WO3/TiO2 composite films displayed exceptional EC stability, with no significant degradation observed over 2500 cyclic voltammetry cycles. This superior EC performance can be attributed to the synergistic effect between the hexagonal WO3 NRs and anatase TiO2. This study highlights the significance of the synthesis method and the unique structural characteristics of the composite in enhancing the EC performance.