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

An all solid-state electrochromic device (ECD) was formed by anodically colored 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 were electrochemically deposited on SnO2. The transmission spectra of ECD were 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 determined. The influence of the experimental parameters (electrolyte pH in the range 0.65-7.65, coloration potential) was studied; good coloration reversibility and memory effect can be obtained up to pH = 7.65. A typical device presented a coloration time of approximate to 30 s and a shorter (< 10 s) bleaching 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 electrolyte has many advantages: its pH can be set to the best value, rather high, and the structure of the PANI/PAMPS interface allows to explain the presence of conductivity even at high pH. The excellent reversibility of ECD is associated to the presence of an optical free-carriers tail. (C) 1998 Elsevier Science Ltd. All rights reserved.