A WO 3 Nanoporous-Nanorod Film Formed by Hydrothermal Growth of Nanorods on Anodized Nanoporous Substrate

Abstract

© The Author(s) 2015. Published by ECS. A tungsten oxide (WO 3) nanoporous-nanorod film was produced for the first time by hydrothermally growing WO 3 nanorods on nanoporous WO 3 substrate. The nanoporous substrates were prepared using the anodization method; hydrothermal reaction was performed on as-anodized and annealed (200-500°C) nanoporous substrates for nanorod growth. The as-anodized substrate and the substrates annealed at ≤300°C dissolved after hydrothermal reaction because of the amorphous and low crystallinity behaviors of the WO 3 substrates. However, the substrates annealed at ≥400°C did not dissolve during the hydrothermal reaction; instead, nanorods were grown on the substrates, forming a nanoporous-nanorod structure. The WO 3 nanoporous-nanorod film (nanorods grown on substrate annealed at 400°C) showed good electrochromic properties with high current density (-13.22 and +7.30 mA cm -2), good cycling stability, and short coloring (∼6 s) and bleaching (∼3.4 s) times. These good properties are attributed to the combination of two nanostructures (nanoporous and nanorods) that contributed to a large WO 3 surface area.