Reduced graphene oxide-induced in-situ uniform growth of hydrated WO₃ film for enhanced electrochromic performance

WO₃-graphene electrochromic materials are widely used in electrochromic devices including smart windows and electronic displays, due to their ability to adjust optical transmittance in the visible and near-infrared ranges under low electrode potential. However, the uniformity of the film remains a challenge for the widely used physical mixing-coating method. In this study, we present a two-dimensional material-assisted synthesis of a porous hydrated WO₃ film (WH-rGO) based on reduced graphene oxide (rGO) nanosheets and WO₃ (rGO-WO₃) seed layer via a hydrothermal method. The incorporation of rGO not only promotes the uniform growth of hydrated WO₃ film, enhancing ion transport but also introduces oxygen vacancies, creating an efficient conduction pathway for charge transport. The resulting WH-rGO film exhibits impressive performance, achieving 71% optical modulation at 700 nm, with bleaching and coloring times of 4.2 and 1.0 s. The coloration efficiency is calculated at 156.11 cm²·C⁻¹, and the optical modulation is maintained at 93% of the initial optical modulation after 1000 cycles applied in the +1.0 and −1.1 V potential ranges. This work offers new insights into the role of oxygen vacancies in enhancing the electrochromic properties of hydrated WO₃ films through the addition of rGO. It also provides a promising approach for the synthesis of electrochromic materials, facilitating their application in smart window technologies.