Polyaniline as a Reversibly Switchable Electrochromic Material
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POLYANILINE AS A REVERSIBLY SWITCHABLE ELECTROCHROMIC MATERIAL WOAN-RU SHIEH*,
SZE C. YANG*,
CHARLES MARZZACCO#,
JYUN-HUEI HWANG*
*Department of Chemistry, The University of Rhode Island, Kingston, RI 02881 #Department of Physical Sciences, Rhode Island College, Providence, RI 02908 INTRODUCTION Polyaniline is an interesting electrochromic material because its color can be changed from clear to green, to blue, and to purple by electrochemical oxidation[l]. The structural transformations associated with these color changes are shown in Scheme I. One of the possible applications for polyaniline is to use it as the active material in electrochromic windows. An electrochromic window is a multi-layered device (Scheme II) with the structure of a transparent rechargeable battery. A practical electrochromic window needs to have long color-cycling lifetime and good durability under solar radiation. This is a severe requirement because all layers of materials in Scheme II and interfaces between layers have to be durable under _a I ",N
Leucoemeraldine
I _I N
N
(Clear)
Oxidation
Reduction
I a I I_ I Ernradi n, al Emeraldoe Sal
SH
H
H
H l
N
N
N
N-
J
Oxidation
Reduction ý_a
H~oEmeraldine N-a NO
j
Reduction
N-
(Green)
N
Base -N-
(Blue)
Oxidation
NN-0N-
1
Pernigranillne
Base
(Purple)
Ix
Scheme I
Oxidation and Reduction of Polyaniline •.Jr
Glass /Tnn
Oxide or Gold
Polyanllln"
Electrolyte CounterElectrode Gloses
Scheme II
Diagram of An Electrochromic Wlindow
Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials Research Society
330
such electrochemical and photochemical stress. In this communication we report an initial study towards the We concerned construction of a polyaniline-based electrochromic window. ourselves with only half of the device shown in Scheme II, which consists We tested such a half-cell in an polyaniline coated on tin oxide glass. aqueous electrolyte to see if this part of the electrochromic device can be made durable enough for electrochromic applications and to find useful Our tests were confined designing principles for constructing good devices. to switching between the clear and the green colors of polyaniline because its purple form is known to have limited electrochemical stability[2]. RESULTS AND DISCUSSION Electrochemical Stability of Polyaniline Thin film polyaniline was polymerized from acidic aniline monomer solution (1.5 M aniline in 3 M HCMsolution) by potentiostatic (0.65 V vs. Tin oxide coated on glass was used as a S.C.E.) electrochemical oxidation. transparent working electrode and platinum was used as a counter electrode. Details of the synthesis and the optical spectra of polyaniline films have been reported in reference 1. During the electro-polymerization, a thin film of polyaniline (about 500 nm in thickness) adheres to tin oxide electrode surface. For convenience in the following discussion we designate the sample as S-type polyaniline/SnO2 which denotes polyaniline synthesized by potential Static electrolysis and coated on a Sn0 2 coated gl
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