Ta ²O ⁵-incorporated WO ³ nanocomposite film for improved electrochromic performance in an acidic condition

We report electrochromic and electrochemical properties of a WO ₃-Ta ₂O ₅ nanocomposite electrode that was fabricated from co-sputtering. Transmission electron microscopy (TEM) images of the WO ₃-Ta ₂O ₅ nanocomposite electrode revealed that morphology of the WO ₃ film was changed by incorporation of Ta ₂O ₅ nanoparticles, and their chemical states were confirmed to be W6 ⁺ and Ta ⁵⁺ oxides from X-ray photoelectron spectroscopy (XPS). The introduction of Ta ₂O ₅ to the WO ₃ film played a role in alleviating surface roughness increase during continuous potential cycling; whereas the surface roughness of the WO ₃ film was increased from ca. 3.0 nm to ca. 13.4 nm after 400 cycles, the roughness increase on the WO ₃-Ta ₂O ₅ was significantly reduced to 4.2 nm after 400 cycles, as investigated by atomic force microscopy (AFM). This improvement of the stability by adding Ta ₂O ₅ may be responsible for the enhanced electrochemical and optical properties over long-term cycling with the WO ₃-Ta ₂O ₅ nanocomposite electrode.