Proceedings of 2nd International Symposium for Color Science and Art 2020

Durability Improvement of Electrochromic Display withNano-Structured ElectrodeKatsumi Yamada, Shota Tsuneyasu, Fukuro Koshiji, Takayuki Uchida,and Toshifumi SatohTokyo Polytechnic Univ., 1583 Iiyama, Atsugi, Kanagawa 243-0297, JapanABSTRACT

2. Experimantals
2.1 Preparation of ITO Electrode Modified with Au
Nano-island (Au-ITO)
Au nano-island was immobilized on ITO electrode byelectrochemical deposition with pulse voltage (11 V) andconstant voltage (1.0 V). This reaction was carried out
using an aqueous solution of Au (I) trisodium disulphite
and potassium sulfite at room temperature.

Au nano-islands were immobilized on ITO electrodes
by pulse electrolysis.
Poly(pyrrole) [PPy] waselectrochemically polymerized using the nano-structured
electrode (Au-ITO). The electrochromic changes of PPy
on the Au-ITO could be more stable than one on an
untreated ITO electrode.
1. INTRODUCTION
Recently, we reported that the electrochromic (EC)
response of conductive polymers could be improved byusing Au nano-particles with island structure immobilized
on transparent electrode. These nano-structures wereeasily obtained by sputtering or electrochemical
deposition. In order to improve the EC response, theenhancement of coloring by plasmonic electric fields of Au
nano-particles (with a particle size of several tens ofnanometers) contributes to the thinning of EC materialfilms. [1,2] The dielectric-metal-dielectric (DMD) structure
formed between these particles probably improve theelectrical conductivity of the EC material.
The stability of EC changes was focused on this study
as the effect on the EC characteristics by using thenano-structured electrode. It is well known that the redox
reaction of conductive polymer is accompanied by a large
and powerful volume changes. We believe that thepolymer film detachment from the electrode due to volume
changes play the great role to the deactivation of the ECchanges.

2.2 Preparation of Poly(pyrrole) Film
The PPy films were prepared on the electrode by anelectropolymerization with a cyclic potential application
between -500 mV and +800 mV (vs. Ag-AgCl, scan rate:
50 mV/s). The polymerization solution was 10 mM pyrrole
and 0.1 M lithium perchlorate (LiClO4) dissolved in water.
2.3 Transmittannce measurement
The EC characteristics of the PPy on the electrodewere evaluated by the transmittance measurement in thetransparent glass cell. Fig. 1 shows the schematic
diagram of the transparent glass cell.
3. RESULTS AND DISCISSION
3.1 Polymerzation

Au Plate
Au-ITO
ITO+ 0.09

Current / mA+ 0.06

+ 0.03

+0.00

-0.03

-0.06
-600

-400-200

0+ 200 + 400 + 600 + 800 + 1000

Potential / mV(Vs.Ag-AgCl)

Fig. 2 Cyclic voltammograms (scan rate : 50 mV/s) ofthe pyrrole polymerization on ITO, Au-ITO and Au
plate electrodes at the first potential scanning.

Fig. 1 Schematic diagram of the transparent glasscell.

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Proceedings of 2nd International Symposium for Color Science and Art 2020
Fig. 2 shows cyclic voltammograms at the time of thefirst scan during polymerization using the ITO electrodeand the Au-ITO electrode. Comparing the monomer
oxidation currents at +800 mV, the Au-ITO shows about
10 times larger current value than the ITO electrode.
Generally, this current is considered to be a mixture of acurrent for monomer oxidation and a current for oxidationof a polymer adsorbed (or deposited) on an electrode. On
the cyclic voltammogram, oxidative currents for potential
scan in negative direction from +800 mV were smaller thanthat in positive direction to +800 mV. It indicates that
conductive polymers has never deposited on the electrodesurface. These results suggest that the Au-ITO electrode,in which three-dimensional Au nano-structures arepresent in the form of islands, has a significantly larger
effective electrode surface area for monomer oxidation
than the ITO electrode. In particular, there is a large
difference in the monomer oxidative potentials between
Au-ITO and ITO. The value of the Au-ITO electrode ismore negative (at least 200 mV) than the ITO electrode).
By lowering the applied
potentials
for theelectropolymerization of pyrrole in an aqueous solution, it
is possible to suppress a degradation reaction such ashydrolysis
occurring
simultaneouslywith
thepolymerization reaction. Decomposition sites generated
during the polymerization with positive potentials have a
disconnection of π-conjugate structure, which probably
accelerates the decomposition reaction in entire film.

continuous activity decay was observed from 2nd cycle.
On the other hand, in the case of Au-ITO, the decay issuppressed up to 7th cycle. A significant difference in thestability was found between Au-ITO and ITO.
3.3 EC stability
As the demonstration of EC stability, fig. 4 showed achange in transmittance at a wavelength of 700 nm whencontinuous cyclic scans (50 mV/s) of the applied potential
between -500 mV and +450 mV were carried out on PPy
film immobilized on each electrode. For PPy films on bothelectrodes, the transmittance increased and decreased
periodically due to redox reaction. In the ITO, the amountof change in transmittance had been reduced since the2nd cycle. On the other hand, in the case of the Au-ITO,
the amount of change was stable until the 7th cycle. Inaddition, subsequent decay (after 8th cycle) of the change
was slower than that of ITO.

Tran. at 700 nm / %PPy/ITO
PPy/Au-ITO

3.2 Electrochemical Activity
0Electrochemical avtivity / %400Time / s100Fig. 4 Electrochromic stabilities of the PPy films on
the Au-ITO or ITO electrodes for applied potentialcycles.

8060200

PPy/Au-ITO
PPy/ITOThe decomposition reaction seemed to be faster,probably because the aqueous solution was used as theelectrolyte. About both electrochemical activity and EC
stability, better results were obtained from the Au-ITO. It isconcluded that the detachment of the polymer film issuppressed by the three-dimensional nano-structure
existing on the ITO electrode surface.

40100200300

400

Time / sFig. 3 Electrochemical stabilities of the PPy films on
the Au-ITO or ITO electrodes for applied potentialcycles.

4. REFERENCES

In order to compare the decay in the electrochemical
activity of PPy film on each electrode, continuous cyclic
scans (50 mV/s) of the applied potential between -500 mVand +450 mV were carried out for the PPy films on eachelectrode in the polymerization solution. Fig. 3 shows theelectrochemical activities of the PPy films for each cycle,
where the activity value of 100% was the reduction current
at 0 mV in the first cycle. In the case of ITO electrode, a[1] Y. Tanaka and K. Yamada, J. Soc. Photogr. Sci.
Technol. Jpn., pp.60-61, Vol. 80, (2017)[2] K. Yamada, F. Koshiji and T. Uchida, Bull. Soc. Photogr.
Imag. Japan, pp.18-22, Vol. 28, (2018)34