Electrochromic behaviour by lithiation process of nanocomposites based on WO3 nanofibers / electrochemically reduced TiO2

• WO 3 NF/TiO 2 R nanocomposite synthesized on FTO for electrochromic use. • electrospinning and reduction steps influence the structure, band gap, and defects. • the nanocomposite has fast response times: 3.5 s for coloration, 4 s for bleaching. • durable for 1000 cycles and promising for smart window applications. A new WO 3 NF/TiO 2 R electrochromic nanocomposite was synthesized on FTO substrate using a dip-coating technique combined with an electrochemical reduction treatment to induce defects in the reduced TiO 2 lattice (TiO 2 R), followed by electrospinning deposition of WO 3 nanofibers (WO 3 NF). The parameters used for electrospinning WO 3 NF and the electrochemical reduction treatment applied to the TiO 2 layer affected the structural, optical, band gap and Urbach energy value, intrinsic defects, and electrochromic features of the resulting nanocomposite film. The electrochromic properties of the WO 3 NF/TiO 2 R nanocomposite in a Li + electrolyte exhibited a colouration efficiency of 161.84 cm 2 C –1 , an optical modulation (ΔT) of 75.41 %, a reversibility of 61.31 %, and rapid response times of 3.5 s for colouration and 4 s for bleaching. The structure of the interconnected nanocomposite makes more places for redox reactions and speeds up charge transport. The WO 3 NF/TiO 2 R/FTO electrode had good capacitive behaviour, low charge resistance, and good durability for 1000 voltammetry cycles. .The structure of the interconnected nanocomposite provides more sites for redox reactions and speeds up charge transport. The WO3NF/TiO2R/FTO electrode had good capacitive behaviour, low charge resistance, and good durability for 1000 voltammetry cycles.