Electrodeposited Gold Nanostructures for the Enhancement of Electrochromic Properties of PANI-PEDOT Film Deposited on Transparent Electrode

Abstract

Conjugated polymers (CPs) are attractive materials for use in different areas; nevertheless, the enhancement of electrochromic stability and switching time is still necessary to expand the commercialization of electrochromic devices. To our best knowledge, this is the first study demonstrating the employment of electrodeposited gold nanostructures (AuNS) for the enhancement of CPs' electrochromic properties when a transparent electrode is used as a substrate. Polyaniline-poly(3,4-ethylenedioxythiophene) (PANI-PEDOT) films were electrodeposited on a transparent indium tin oxide glass electrode, which was pre-modified by two different methods. AuNS were electrodeposited at -0.2 V constant potential for 60 s using both the 1st method (synthesis solution consisted of 3 mM HAuCl₄ and 0.1 M H₂SO₄) and 2nd method (15 mM HAuCl₄ and 1 M KNO₃) resulting in an improvement of optical contrast by 3% and 22%, respectively. Additionally, when using the 1st method, the coloration efficiency was improved by 50% while the switching time was reduced by 17%. Furthermore, in both cases, the employment of AuNS resulted in an enhancement of the electrochromic stability of the CPs layer. A further selection of AuNS pre-modification conditions with the aim to control their morphology and size can be a possible stepping stone for the further improvement of CPs electrochromic properties.

Keywords: conducting polymers; electrochromic polymers; gold nanostructures; poly(3,4-ethylenedioxythiophene); polyaniline.

Figure 1

Electrochemical deposition of gold nanostructures (AuNS) on an indium tin oxide (ITO) electrode. Inset: Photographic pictures of ITO/AuNS electrodes after electrodeposition from different solutions.

Figure 2

SEM images of (A) ITO/AuNS_I and (B) ITO/AuNS_II deposited at −0.2 V for 60 s from a water-based solutions.

Figure 3

Cyclic voltammograms of (A) ITO/AuNS_I and (B) ITO/AuNS_II recorded in 0.5 M H₂SO₄ solution. The potential sweep rate was 150 mV s⁻¹.

Figure 4

XRD patterns of AuNS deposited on an ITO electrode.

Figure 5

Absorption spectra of AuNS deposited on an ITO electrode.

Figure 6

(A) Cyclic voltammograms obtained during the synthesis and (B) SEM images of polyaniline–poly(3,4-ethylenedioxythiophene) (PANI-PEDOT) films on (1) ITO/AuNS_I and (2) ITO/AuNS_II electrodes. Electrochemical synthesis was performed in 0.2 M H₂SO₄ solution containing 0.1 M LiClO₄, the sweep rate of the electrode potential was 50 mV s⁻¹.

Figure 7

The surface topography evaluation of a PANI-PEDOT layer deposited on (1) ITO, (2) ITO/AuNS_I, and (3) ITO/AuNS_II obtained by AFM. The surface section (A) and 2D AFM image (B) are presented.

Figure 8

(A) Absorbance spectra of the PANI-PEDOT layer deposited on different substrates under (dotted lines) −0.1 V and (solid lines) +0.5 V applied potential. (B) Absorbance at λ_max dependency on time during electrochromic switching between −0.1 and +0.5 V potential (measurements were done in 0.2 M H₂SO₄ and 0.1 M LiClO₄ solution when potential was applied vs. Ag/AgCl electrode).

Figure 9

(A) Transmittance curves at λ_max and (B) chronoamperometry results of PANI-PEDOT layers synthesized on (1) ITO, (2) ITO/AuNS_I and (3) ITO/AuNS_II registered in 0.2 M H₂SO₄ with 0.1 M LiClO₄ solution. First 5 and last 146–150 cycles are displayed. The potential was switched between −0.1 V and +0.5 V vs. Ag/AgCl for 10 s at each step.