The relevant electrochemical potential window for the reversible color change of Cs:WO3 NCs was determined by monitoring the change in transmittance as a function of the applied potential using chronoamperometry (Figures and). The potential window and charge capacity found using chronoamperometry were used to determine the appropriate current density to achieve an approximate 1C charging rate of the NC films in each of the four electrolytes. Films were charged with a constant current, and absorbance spectra were taken at set time intervals, corresponding to known amounts of stored charge (Figures and). The ratio of incremental changes in optical density to stored charge determine the coloration efficiency. All absorbance measurements were taken in transmittance mode and backgrounded with a clean piece of ITO coated glass in the electrochemical cell filled with electrolyte. The OD changes are then referenced to the fully transparent state. X-ray diffraction (XRD) of the NC sample was done by precipitating a powder from a dispersion in hexane through the addition of excess isopropanol. The dried powder was mounted on a cryoloop with mineral oil for measurement. A Rigaku R-Axis Spider with a Cu Kα source was used to collect the diffraction pattern. Crystal structure visualizations were created using VESTA. Scanning transmission electron microscopy (STEM) was used to image the NCs. A carbon-coated copper grid was coated with the NC sample by dropping 20 μL of a 1 mg/mL dispersion in hexane. After drying overnight in a vacuum desiccator, the sample was imaged using a Hitachi S5500 microscope in STEM mode.