Elaboration and study of a PANI/PAMPS/WO3 all solid-state electrochromic device

An all solid-state electrochromic device (ECD) was formed by anodically col ored polyaniline (PANI) and cathodically colored tungstic acid, WO3, 2H(2)O , separated by a protonic conductor solid electrolyte: poly 2-acrylamido 2- methylpropane sulfonic acid, (PAMPS). PANI as well as tungstic acid films w ere electrochemically deposited on SnO2. The transmission spectra of ECD we re displayed using near IR/visible/near UV spectroscopy as well as optical multichannel analysis which allows, in addition, to obtain the kinetics of coloration/bleaching. They were checked after up to 2.10(4) electrochromic cycles extending from -1.2 to +1.2 V; the change of optical density, Delta OD, the coloration yield and the stability during the cycling were determin ed. The influence of the experimental parameters (electrolyte pH in the ran ge 0.65-7.65, coloration potential) was studied; good coloration reversibil ity and memory effect can be obtained up to pH = 7.65. A typical device pre sented a coloration time of approximate to 30 s and a shorter (< 10 s) blea ching time, with Delta OD = 0.4 at 2.23 eV (human eye maximum sensitivity), falling to 0.25 after 2.10(4) cycles. The choice of PAMPS as a solid elect rolyte has many advantages: its pH can be set to the best value, rather hig h, and the structure of the PANI/PAMPS interface allows to explain the pres ence of conductivity even at high pH. The excellent reversibility of ECD is associated to the presence of an optical free-carriers tail. (C) 1998 Else vier Science Ltd. All rights reserved.