CNCs extracted from wood pulp in an aqueous solution with 11.5% weight concentration was provided by the process development center of the University of Maine. It was then added to the peroxipolytungstic acid precursor solution and thoroughly mixed in a blender at room temperature. Prior to film deposition, the ITO-coated glass of 1 mm thickness, purchased from Colorado concept coatings LLC, was cut in pieces of , cleaned by sonication in acetone, isopropyl alcohol and DI for 20 min each, and dried at 110°C for 1 h. To deposit the films, the ITO-coated glass slides were dipped into the well-stirred solution of the precursor mixed with CNC, using a PTL-MM02 dip-coater machine from MTI Corporation, with down- and upward traveling speeds of 45 and , respectively, and a dwell time of 2 min. The structure and morphology of the films were studied using x-ray diffraction (XRD), field emission-scanning electron microscopy, and atomic force microscopy (AFM). The EC performance was analyzed by cyclic voltammetry using a CH Instruments electrochemical analyzer, an Ocean Optics halogen light source, and an UV–vis–NIR spectrometer. A three-electrode cell was used, where the -CNC film on the ITO/glass substrate is the working electrode, Ag/AgCl the reference electrode, and Pt the counter electrode. The electrolyte used in the experiment was a 1M solution of lithium perchlorate () in propylene carbonate ().