WO3 nanorods prepared by low-temperature seeded growth hydrothermal reaction

Highlights: • WO3 nanorods with 5–10 nm diameter were grown directly on seeded tungsten foil. • WO3 nanorods were successfully grown at low temperature of 80 °C. • WO3 nanorods were grown on the entire surface of the seed layer after 24 h. • Annealed nanorods showed better electrochromic properties than as-made nanorods. -- Abstract: 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