Regulating the growth of WO₃ thin films using ammonium acetate as structure directing agent

The optimization of morphology and structure of tungsten trioxide (WO₃) needs to be performed to target some specific applications. In fields such as electrochromics and sensing, the study of electrochemical reaction kinetics is important as it defines the rate of reaction occurring on the WO₃ surface. In the present study, WO₃ thin films are grown on fluorine-doped tin oxide (FTO) glass by in-situ hydrothermal technique. To regulate the growth of the WO₃ layer employing the hydrothermal method, ammonium acetate has been used as a capping agent (CA) and its molar ratio for tungsten, i.e., CA/W, was varied from 0 to 6. Cyclic voltammetry (CV) revealed that the thin film prepared with CA/W of 4 has improved Li⁺ ions intercalation/deintercalation which leads to fast reaction kinetics. Better electrochemical reaction kinetics in WO₃ thin film with a CA/W ratio of 4 compared with the samples having CA/W of 0 and 2 is ascribed to its improved morphology and phase. X-ray diffraction and scanning electron microscopy analysis showed negligible thin film growth with a CA/W ratio of 6. Overall, WO₃ thin film with a CA/W ratio of 4 showed excellent performance, making it a good candidate for electrochromics or other related applications.