Electrochromic properties of tetrabutylammonium perchlorate-doped polypyrrole/ nanocellulose composite films

Abstract

This study investigates electrochromic properties of tetrabutylammonium perchlorate (TBAP)-doped polypyrrole (PPy) and PPy/Nanocellulose (NC) composite films, where TBAP-doped PPy/NC composites were synthesized with various NC content ranging from 0 % to 100 % by volume in 0.1 M pyrrole solution and deposited on fluorine-doped tin oxide (FTO) glass using potentiostatic polymerization. The optimum polymerization time for depositing a uniform, adhesive and stable films on FTO with higher optical contrast between bleached and colored states are found to be 10 s at a constant voltage of 1.2 V. To compare the electrochromic properties of NC-free and NC-containing TBAP-doped PPy films, cyclic voltammetry (CV), chronoamperometry (CA), and optical transmittance spectroscopy were carried out in 0.1 M TBAP electrolyte. A reversible color change from yellow at - 0.6 V (bleached state) to blue gray at + 0.6 V (colored state) is observed for %40 NC-containing TBAP-doped PPy composite film. CV measurements at the potential between - 0.8 V and + 0.8 V show an increase at the oxidation and reduction peak currents up to 60 % NC in TBAP-doped PPy, but the highest optical contrast and uniformity is observed for 40 % NC-containing composite film. And scanning electron microscopy images reveal that surface morphology changes and cluster/agglomerations on the surface of the films are formed when the %NC value exceeds 60 %. Of the NC-containing composite films, the 40 % NC-containing TBAPdoped PPy composite film exhibits the best adhesion to FTO substrate. Furthermore, the highest optical contrast (25.9 % at 700 nm) is observed for %40 NC-containing TBAP-doped PPy when compared to NC-free TBAP-doped PPy film (18.7 % at 700 nm). Therefore, PPy/NC composite with 40 % volume ratio of NC in PPy was selected for further CV and CA experiments. Compared to NC-free films, 40 % NC-containing TBAP-doped PPy exhibits faster switching time (1.16 s), higher optical contrast (25.9 % at 700 nm), higher coloration efficiency (65.6 cm2/C), and better uniformity on FTO. Our results may lead to the design of a high-performance electrochromic devices using NC-Conductive Polymers, with electrochromic and mechanical properties that can be adjusted through NC composition, especially to create flexible composites with enhanced mechanical strength.