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

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.