WO3 nanorods prepared by low-temperature seeded growth hydrothermal reaction

This work describes the first tungsten oxide (WO3) nanorods hydrothermally grown on W foil. WO3 nanorods were successfully grown at low hydrothermal temperature of 80 °C by seeded growth hydrothermal reaction. The seed layer was prepared by thermally oxidized the W foil at 400 °C for 0.5 h. This work discusses the effect of hydrothermal reaction and annealing period on the morphological, structural, and electrochromic properties of WO3 nanorods. Various hydrothermal reaction periods (8-24 h) were studied. Monoclinic WO3 nanorods with 5-10 nm diameter were obtained after hydrothermal reaction for 24 h. These 24 h WO3 nanorods were also annealed at 400 °C with varying dwelling periods (0.5-4 h). Electrochromic properties of WO3 nanorods in an acidic electrolyte were analyzed using cyclic voltammetry and UV-vis spectrophotometry. WO3 nanorods annealed at 400 °C for 1 h showed the highest charge capacity and the largest optical contrast among the 24 h WO3 films. The sample also showed good cycling stability without significant degradation. Based on the results, the reaction mechanism of WO3 nanorod formation on W foil was proposed.