Water processable Prussian blue–polyaniline:polystyrene sulfonate nanocomposite (PB–PANI:PSS) for multi-color electrochromic applications

Abstract

A new nanocomposite, Prussian blue–polyaniline:polystyrene sulfonate (PB–PANI:PSS), has been synthesized by incorporating both polyaniline (PANI) and Prussian blue (PB) electrochromic materials. The PB–PANI:PSS nanocomposite is synthesized by two-step polymerization, and the nanocomposite thin film is prepared by a wet-coating method on the conductive ITO glass. The PB–PANI:PSS thin film shows three optical states: highly transparent in a reduced state (−0.5 V vs. Ag/AgCl), green color at +0.2 V contributed by PANI, and blue-green color at +0.5 V contributed by both PANI and PB. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) mapping images show that the PB pigments were well dispersed in the PANI:PSS matrix. FTIR spectra show the specific absorbance peaks of both PANI:PSS and PB in the nanocomposite film. Cyclic voltammetry (CV) analysis reveals two redox pairs from the PB–PANI:PSS thin film. The UV-Vis absorbance spectra show a broader absorbance range for the nanocomposite than for pure PANI and PB. An averaged transmittance (T_ave) was established to evaluate this wide-range absorbance material. The ΔT_ave value was 52.3% when applying an operation voltage between −0.5 and +0.5 V, and the switching times were 8.1 and 13.3 s for bleaching and darkening, respectively. The coloration efficiency was calculated to be 76.6 cm² C⁻¹ at the averaged visible wavelength. This PB–PANI:PSS composite thin film could potentially be useful for multi-color electrochromic applications because the ease of processing using water may facilitate the preparation of large-area thin films.