The electrochromic responses of the NC films were investigated using in situ spectroelectrochemistry. A NC film served as the working electrode in an optically transparent electrochemical cell controlled by a Biologic VMP3 potentiostat, which was placed between fiber optic cables coupled to an ASD Quality Spec Pro visible-near infrared spectrometer. For lithium electrolytebased experiments, a lithium foil was used as both the counter and reference electrodes. For measurements utilizing other electrolyte cations, a silver/silver cation reference electrode and a platinum foil counter electrode were used. All electrolytes were prepared in propylene carbonate at 0.1 M concentration of metal hexafluorophosphate salt of formula XPF6, where X is either Li + , Na + , K + , or tetrabutylammonium (TBA + ).