## 3 Results and Discussion
### Chemical Analysis of Reduced Films  
The spectroelectrochemical analysis has shown that PEG 600 in combination with PIB\({}_{50}\)-b-PEO\({}_{45}\) as structure-directing agents led to WO\({}_{3}\) films with optimum electrochromic switching characteristics (Table 8, Figures 7b, 9b and S13c). For films prepared with just PEG 600 or PEG 400 as additive, switching characteristics almost as good (Table 8, Figures 7a, 10b, S11a, S12a,b and S13b) were achieved. From a technological point of view,application of PEG only provides other advantages over using both, PEG and PIB\({}_{50}\)-\(b\)-PEO\({}_{45}\). The preparation of the films is not only saving the additional demanding precursor but also saves time and energy since a heat treatment of the films is only needed at 250 \({}^{\circ}\)C for one hour as opposed to 300 \({}^{\circ}\)C for 12 h. Therefore, and in order to allow further optimization of such films in the future, details of the intercalation reactions and of the charge transport were studied for WO\({}_{31}\)up400 and WO\({}_{31}\)up600 and compared to WO\({}_{31}\)comp. The presence of reduced states of WO\({}_{3}\) was directly proven by XPS analysis (Figure S16 vs. Figures 4 and S4-S7) after applying \(-\)1.0 V for 300 s in the electrochemical cell and subsequent transfer to vacuum. All films showed an increase in the concentration of W\({}^{5+}\) from around 0.3-2.8% in the pristine state to 16-38% in the reduced state (Figure S8b, Table 4), comparable to the values of 30-35% reported for colored WO\({}_{3}\) films prepared by a cathodic arc plasma [65]. A trend of higher concentrations of W\({}^{5+}\) (at least at the surface) in WO\({}_{31}\)up400 and WO\({}_{31}\)up600 and to lower concentrations in WO\({}_{31}\)mp and WO\({}_{31}\)ummp, also when compared to WO\({}_{31}\)comp was observed. Efficient reduction of microporous WO\({}_{3}\) was thereby confirmed. Despite high coloration of WO\({}_{31}\)ump and low coloration of WO\({}_{31}\)mp, both these mesoporous films showed a similarly low concentration of W\({}^{5+}\) and degree of reduction \(x\), in line with a high \(CE_{710\rm nm}\) observed for WO\({}_{31}\)ummp, but rather low \(CE_{710\rm nm}\) for WO\({}_{31}\)mp (Table 8). Ar\({}^{+}\)-sputtering of the reduced films with intercalated Li\({}^{+}\) allowed to discuss the depth profile of the redox reactions. The concentration of W\({}^{5+}\) for the reduced films decreased and then saturated with proceeding etching time, i.e., deeper in the films (Figure S8). This is consistent with a reduction reaction proceeding from the surface towards the inner volume of the films as would be expected for a movement of e\({}^{-}\) still faster also in porous WO\({}_{3}\) than Li\({}^{+}\), which can be expected to be fast within the pores but slow within solid, albeit porous WO\({}_{3}\), as confirmed by increased but still quite moderate \(D_{\rm CV}\) (Table 7). The subsequent reduction to W\({}^{4+}\), W\({}^{5+}\) and W\({}^{0}\) occurred faster than in the pristine films, reasonable in view of a start already in a reduced state of WO\({}_{3}\) (Figure S16). To directly prove the impact of the microporous network and to complement this analysis, the distribution of Li\({}^{+}\) in the reduced films was also analyzed by ToF-SIMS (Figures 11 and S17). The WO\({}_{3}\)\({}^{-}\) and the SnO\({}^{-}\) signals (Figure 11) are used for correlating the sputter times and the etched thickness of the films. For the WO\({}_{31}\)up400 and WO\({}_{31}\)up600 samples, the decrease in intensity of the WO\({}_{3}\)\({}^{-}\) signal and the increase in intensity of the SnO\({}^{-}\) signal occurred at longer sputter times compared to the WO\({}_{31}\)comp films, well in line with a higher film thickness for WO\({}_{31}\)up400 and WO\({}_{31}\)up600 (Table 5). A rather constant sputter rate of about 0.3 nm/s was obtained for all films.