## 3 Results and Discussion
### Elemental Composition, Density, Surface Area and Porosity

Table 4: Concentration of W\({}^{5+}\) in pristine (p) and intercalated (i) WO\({}_{3}\) thin films obtained from XPS and the degree of reduction for these experiments expressed as Li\({}^{+}\) content \(x\) in Li\({}_{x}\)WO\({}_{3}\). \begin{table}
\begin{tabular}{c c c c c c} \hline
**Film Type** & **W 4f/\%** & **-OH/\%** & **O=W/\%** & **C/\%** & **(O:W)\({}_{\rm XPS}\)** \\ \hline WO\({}_{31}\)comp & 15.72 & 9.46 & 44.23 & 29.79 & 3.42 \\ WO\({}_{31}\)up4  
difference between \(P_{\text{chem}}\) and \(P_{\text{E}}\). Both methods, however, independently yield the same trend of increasing porosity when using the polymers as structure-directing agents with \(P(\text{WO}_{31}\,\text{up}400)<P(\text{WO}_{31}\,\text{up}600)<<P(\text{WO}_{3 1}\,\text{mp})<<P(\text{WO}_{31}\,\text{amp})\). The combination of PIB\({}_{50}\)-\(b\)-PEO\({}_{45}\) and PEG 600 as additives clearly provided the highest porosity as already revealed by SEM (Figure 1c). The specific surface area \(S_{\text{BET}}\) of the as-prepared films was analyzed from the BET plots obtained from Kr physisorption (77 K) shown in Figure S9. The WO\({}_{31}\,\text{mp}\) sample was annealed at 550 \({}^{\circ}\)C for 1 h before the BET analysis to remove any residual polymer and obtain a measure for the intrinsic surface area of WO\({}_{3}\), albeit transformation to crystalline WO\({}_{3}\) under such conditions. For the WO\({}_{31}\,\text{comp}\) films prepared without additives, no significant \(S_{\text{BET}}\) could be determined, as expected for a compact thin film. For the WO\({}_{31}\,\text{up}600\) films, a significant surface area of around 3 m\({}^{2}\)/g was obtained, comparable to the surface area reported for WO\({}_{3}\) powder (\(\sim\)2 m\({}^{2}\)/g) [54]. Such surface area is compatible with the presence of micropores between grains of the films (Figure 1d). The values of \(S_{\text{BET}}\) of the WO\({}_{31}\,\text{mp}\) films and WO\({}_{31}\,\text{\upmu}\)mp films turned out in the same range as reported for WO\({}_{3}\) nanoflakes (\(\sim\)10 m\({}^{2}\)/g [55]) and mesoporous WO\({}_{3}\) (\(\sim\)32 m\({}^{2}\)/g [31]). \(S_{\text{BET}}\cong\) 10 m\({}^{2}\)/g determined for the WO\({}_{31}\,\text{mp}\) films thereby confirmed the presence of mesopores within the films but the considerably higher \(S_{\text{BET}}\cong\) 20 m\({}^{2}\)/g of the WO\({}_{31}\,\text{\upmu}\)mp films shows the significantly increased accessibility of the mesopores by the simultaneous presence of micropores serving as interconnecting channels. These \(S_{\text{BET}}\) values appear quite small, compared to the surface area and pore volume usually measured for templated metal oxides. Note that the BET surface area is referred to the mass and that WO\({}_{3}\) has a quite high density (ca. 4.2-7.2 g cm\({}^{-3}\)), thus resulting in lower \(S_{\text{BET}}\) values compared to a material with identical porosity, but smaller skeleton density, e.g., SiO\({}_{2}\) (\(\rho\cong\) 2.2 g\(\cdot\)cm\({}^{-3}\)[53]). For instance, a value of \(S_{\text{BET}}\cong\) 20 m\({}^{2}\)/g (WO\({}_{31}\,\text{\upmu}\)mp), assuming an identical pore space, translates into a value of \(S_{\text{BET}}\cong\) 65 m\({}^{2}\)/g for a corresponding SiO\({}_{2}\) material, which is in accordance with a network of connected spherical mesopores of ca. 20 nm in diameter.