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

Surface wettability conversion of WO3 was investigated through electrochemical or photochemical reaction on a polycrystalline WO3 electrode. The initial water contact angle for the WO3 electrode was about 15 degrees, and it was slightly reduced to 9 degrees by cathodic polarization in water under darkness. In contrast, when the WO3 electrode was irradiated with visible light during anodic polarization, the water contact angles were drastically decreased to below 3 degrees. 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 WO3. On the basis of these results, we discuss a possible mechanism for the surface wettability conversion of WO3. We found that photogenerated holes are indispensable in achieving superhydrophilic conversion on the surface of WO3, whereas the reduction in WO3 by electrons could only generate a slight hydrophilic change.