Highly Thermally Stable and Transparent WO3–SiO2 Gasochromic Films Obtained by an Automated Printing Method

Although smart energy-saving windows, such as electrochromic, thermochromic, and gasochromic windows, show promising applications, they are still being delayed due to the lack of suitable methods for large-area manufacturing. To meet the demands of low cost and fast fabrication, printing methods have been widely studied for electrochromic film deposition. However, hydrogen diffusion depends on the porosity of gasochromic films, which renders the use of usual printing inks impracticable. In this study, a novel kind of WO3/SiO2 ink with suitable rheological characteristics for gasochromic windows was developed by prehydrolyzing and condensing SiO2 in a neutral solution. The kinetics were explored using nuclear magnetic resonance and density functional theory, indicating that the SiO2 growth directions can be controlled at various pH values. The prehydrolysis of SiO2 in a neutral solution exhibits adequate mechanical robustness, suitable rheological characteristics, and stable thermodynamics. Based on the prehydrolysis of SiO2 sol, porous SiO2 skeletons supporting WO3 gasochromic films were synthesized by using automated printing methods, which exhibit a high transmittance of 90%, a high solar energy shielding property of 84%, and good annealing stability at 150 °C. In actual energy-saving tests, the as-prepared gasochromic windows show a much slower rate of increase in room temperature compared to normal windows.