The differences in spectral line shape between the samples reduced in each of the electrolytes suggest that there are different electrochromic mechanisms depending on which interstitial sites are occupied. Films reduced in Li + and Na + electrolytes show similar spectral line shapes, while the same can be said for films reduced in K + or TBA + electrolytes. If the occupation of the various interstitial sites in the hexagonal crystal lattice contributed equally to the electrochromism, one would expect changes only in the magnitude of the optical density change (ΔOD), but not in the line shape. The overall line shape of the ΔOD spectra of the films reduced in K + or TBA + electrolytes show similar shape to the LSPR spectrum of the NC film prior to annealing as shown in Figure . This similarity suggests that the electrochromism in these films is the result of purely LSPR modulation. The LSPR modulation in other metal oxide NC systems is consistent with the results shown here, where there is minimal LSPR peak shift, but substantial LSPR intensity increase with electrochemical reduction. The minimal LSPR peak shift is attributed to the filling of a depletion layer near the surface of the NCs, which results in only modulation of the LSPR active volume, but not the overall carrier concentration. The films reduced in Li + or Na + electrolytes show a significant modulation in the visible region (12,500-25,000 cm -1 ), which is not present for the films reduced using the larger cations. The increased modulation in the visible region suggests that the intercalation of the smaller cations results in a secondary mechanism of electrochromism.