Surface Wetting Behavior of a WO3 Electrode under Light-Irradiated or Potential-Controlled Conditions

Surface wettability conversion of WO 3 was investigated through electrochemical or photochemical reaction on a polycrystalline WO 3 electrode. The initial water contact angle for the WO 3 electrode was about 15°, and it was slightly reduced to 9° by cathodic polarization in water under darkness. In contrast, when the WO 3 electrode was irradiated with visible light during anodic polarization, the water contact angles were drastically decreased to below 3°. The wettability conversions under aerobic or humid atmospheres were also evaluated, and the presence of oxygen and water molecules was important for the hydrophilic conversion of WO 3 . On the basis of these results, we discuss a possible mechanism for the surface wettability conversion of WO 3 . We found that photogenerated holes are indispensable in achieving superhydrophilic conversion on the surface of WO 3, whereas the reduction in WO 3 by electrons could only generate a slight hydrophilic change.