Constructing Bi₂WO₆-decorated TiO₂ composite films for photocathodic protection of 304 stainless steel

Bi₂WO₆ nanoplate/TiO₂ nanowire and Bi₂WO₆ nanoflower/TiO₂ nanowire composite films were successfully prepared using a hydrothermal method. The results show that the light absorption for Bi₂WO₆/TiO₂ composite films is extended to the visible region after Bi₂WO₆ nanoplates and nanoflowers are assembled onto TiO₂ nanowires. Furthermore, Bi₂WO₆ nanoflower/TiO₂ nanowire composite film exhibits a better absorption property compared to Bi₂WO₆ nanoplate/TiO₂ nanowire film, which is mainly ascribed to the narrower bandgap of Bi₂WO₆ nanoflower compared to that of Bi₂WO₆ nanoplate. The photocurrent density for Bi₂WO₆ nanoflower/TiO₂ nanowire and Bi₂WO₆ nanoplate/TiO₂ nanowire composite films can reach 95 and 62.5 μA cm⁻², respectively, which are much higher than that obtained for a pure TiO₂ nanowire film (25 μA cm⁻²). Meanwhile, under illumination, the pure TiO₂ nanowire, Bi₂WO₆ nanoplate/TiO₂ nanowire and Bi₂WO₆ nanoflower/TiO₂ nanowire films can reduce the potential of the coupled 304 stainless steel in 3.5 wt.% NaCl solution by 299, 719 and 739 mV, respectively. Thus, Bi₂WO₆ nanoflower/TiO₂ nanowire film is found to provide the best effective photocathodic protection for 304 stainless steel. This work not only provides an example of shape-dependent photocathodic protection based on Bi₂WO₆ but also opens up new possibilities to design an ideal microstructure on the basis of semiconductor materials for future applications of photocathodic protection.