Color Tuning of Electrochromic TiO₂ Nanofibrous Layers Loaded with Metal and Metal Oxide Nanoparticles for Smart Colored Windows

Co-axial electrospinning was applied for the structuring of non-woven webs of TiO₂ nanofibers loaded with Ag, Au, and CuO nanoparticles. The composite layers were tested in an electrochromic half-cell assembly. A clear correlation between the nanoparticle composition and electrochromic effect in the nanofibrous composite is observed: TiO₂ loaded with Ag reveals a black-brown color, Au shows a dark-blue color, and CuO shows a dark-green color. For electrochromic applications, the Au/TiO₂ layer is the most promising choice, with a color modulation time of 6 s, transmittance modulation of 40%, coloration efficiency of 20 cm²/C, areal capacitance of 300 F/cm², and cyclic stability of over 1000 cycles in an 18 h period. In this study, an unexplored path for the rational design of TiO₂-based electrochromic device is offered with unique color-switching and optical efficiency gained by the fibrous layer. It is also foreseen that co-axial electrospinning can be an alternative nanofabrication technique for smart colored windows.