A polystyrene/WO3 opal composite monolayer film as a building block for the fabrication of 3D WO3 inverse opal films

Abstract

Large area polystyrene (PS)/WO₃ opal composite monolayers were successfully fabricated via a modified “dynamic-hard-template” infiltration strategy. These composite monolayers were then used as building blocks for the synthesis of three-dimensional (3D) WO₃ inverse opal (IO) films in a bottom-up approach. To achieve this, a PS/WO₃ opal composite monolayer serves as a support upon which another PS/WO₃ opal composite monolayer is added, and so on, one over the other, rendering possible, after removal of the PS spheres template, the fabrication of large area 3D WO₃ IO films. Similarly, bilayer, and trilayer WO₃ IOs with large area, having the same pore sizes from layer to layer, can be obtained by repeatedly applying this strategy. This approach also allows control over hierarchical porosity and film thickness by simply changing the diameter of the sacrificial colloidal template and/or the inorganic precursor used in each layer. 3D WO₃ IO films fabricated with this technique exhibit good electrochemical reversibility, cycling stability, and increased coloration efficiency (CE) as the number of WO₃ IO layers is increased.