Electrodeposition of lead on ITO electrode: Influence of copper as an additive

Article abstract of DOI:10.1016/j.electacta.2004.08.021

The reversible electrodeposition of metallic lead onto indium-tin oxide coated glass (ITO) was investigated and the influence of Cu(NO₃) ₂-3H₂O as additive was evaluated. The presence of Cu ²⁺ in the electrolytic solution produces a higher variation in the optical transmissivity. The optical response of the system changes from 85 to 10% relative to the ITO coated substrate. The kinetics of the electroreduction process of the Pb²⁺ and Cu²⁺ from the electrolytes has been determined by electrochemical impedance spectroscopy (EIS) at different electrodeposition potentials. This system may be a promising candidate for electrochromic materials.

Full text of DOI:10.1016/j.electacta.2004.08.021

Electrochimica Acta 50 (2005) 1317–1321
Electrodeposition of lead on ITO electrode: influence
of copper as an additive
∗
´
Cesar O. Avellaneda , Marcos A. Napolitano,
˜
Evandro K. Kaibara, Luis O.S. Bulhoes
Departamento de Qu´ımica, Laborato´rio Interdisciplinar de Eletroqu´ımica e Ceraˆmica-LIEC, Universidade Federal de Sa˜o Carlos,
C.P. 676, CEP 13565-905 Sa˜o Carlos-SP, Brazil
Received 20 February 2004; received in revised form 8 July 2004; accepted 7 August 2004
Available online 5 October 2004
Abstract
The reversible electrodeposition of metallic lead onto indium-tin oxide coated glass (ITO) was investigated and the influence of
Cu(NO3)2·3H2O as additive was evaluated. The presence of Cu2+ in the electrolytic solution produces a higher variation in the optical
transmissivity. The optical response of the system changes from 85 to 10% relative to the ITO coated substrate.
The kinetics of the electroreduction process of the Pb2+ and Cu2+ from the electrolytes has been determined by electrochemical impedance
spectroscopy (EIS) at different electrodeposition potentials.
This system may be a promising candidate for electrochromic materials.
© 2004 Elsevier Ltd. All rights reserved.
Keywords: Electrodeposition; Electrochromism; Impedance spectroscopy
1. Introduction
Ziegler [5] has presented a promising electrochromic sys-
tem based on the deposition–dissolution of metallic bismuth.
Such system comprised a gel electrolyte containing the elec-
trochromic materials (Bi3+, Cu2+ and Br−) sandwiched be-
tween a transparent conducting front electrode and either a
transparent or an opaque rear electrode, depending on the
intended application. Color displays are obtained by mixing
pigments into the gel electrolyte; the cell reaction is given by
the following equation [5].
Electrochromic materials are presently studied for their
possible applications such as smart windows, switchable
automobile rear-view mirrors and flat panel displays [1,2].
There are two groups of materials; the first is related
to ion insertion into hosts such as WO3, Nb2O5, where
the electrochromic material is characterized by its ability
to sustain reversible and persistent changes of the opti-
cal properties when ions (H+, Li+) are intercalated [3]. In
the second group, reversible electrodeposition includes the
deposition–dissolution of metal (electroplating), inorganic
or organic materials onto a transparent conducting substrate
[4,5]. The concept of utilizing reversible electrodeposition
for optical modulation was first proposed in 1929 by Smith
[6]. Some years later, Camlibel et al. [7] and Zaromb [8] re-
ported the reversible electrodeposition of silver for optical
modulation.
−
15Br− + 2Bi3+ + 2Cu2+ = 2Bi0 + 2Cu0 + 5Br3
The effect of copper additives produces changes in the film
morphology. Thus, the influence of the presence of copper
chloride on the electrochemical and optical responses was
also analyzed [5].
Recently, the study of the deposition/dissolution behav-
ior of bismuth in aqueous electrolyte gel media [9] for elec-
trochromic device purposes was reported. The gel was made
from a polymer derived from an animal protein and a large
variation of transmittance values was observed when Cu2+
∗
Corresponding author. Fax: +55 16 2615215.
E-mail address: avellane@dq.ufscar.br (C.O. Avellaneda).
0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2004.08.021

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C.O. Avellaneda et al. / Electrochimica Acta 50 (2005) 1317–1321
was added to the gel. This response can be understood be-
cause copper cations promote Bi/Bi3+ reversibility by a redox
reaction between Cu2+ and metallic bismuth.
On the other hand, the effect of copper as an additive
was explained on the basis of producing self-erasure of
the films, thus avoiding a 3-dimensional growth by favor-
ing 2-dimensional growth. Another important role played
by copper is to increase the electrochemical efficiency,
leading to a more reversible deposition–dissolution process
[10,11].
3. Results
In order to study the influence of copper as additive on
the electrochromic properties of the lead solution, Cu2+ was
added at different concentrations. The corresponding optical
transmittance is shown in Fig. 1. The transmittance decreases
by increasing the amount of copper until it reached an optimal
concentration of 1.84 × 10−3 mol/L. All electrochemical and
optical characterizations were carried out under such condi-
tion.
We report on a system based on the electrodeposi-
tion of lead that could be an interesting candidate for
electrochromic displays. The effect of copper as an addi-
tive on the electrochromic response is also analyzed. The
reduction–oxidation process of lead film electrodeposited in
the presence of copper ions is studied by electrochemical
impedance spectroscopy (EIS).
A typical cyclic voltammogram of electrodeposition and
electrodissolution of lead in the presence and absence of cop-
per is shown in Fig. 2. In the absence of copper, during the
potential scan to more negative values, an increase in the
cathodic current with a maximum close to −0.6 V can be ob-
served. During the anodic scan a current loop characteristic
of a nucleation process is observed. The dissolution current
peak is obtained at a potential close to 0.19 V.
Upon the addition of copper [Cu(NO3)2·3H2O], a 1.8 ×
10−3 mol/L concentration to the Pb2+ solution, a small ca-
thodic peak related to Cu2+ electroreduction is observed at
−0.5 V. No current loop is observed in the current inversion
region. During the anodic scan, the lead dissolution peak
shifts to a more negative potential, and a small dissolution
peak for copper appears at −0.05 V.
2. Experimental
2.1. Transparent conducting electrode
The used transparent conducting working electrode
(1.0 cm × 3.0 cm) was an indium-tin oxide (ITO) coated glass
supplied by Donnelly Corporation with a sheet resistance of
14 ꢀ/ꢀ. The substrate was first ultrasonically cleaned with
acetone and a detergent (Extran from Merck) and rinsed with
double-distilled water, ethanol and then dried at room tem-
perature.
The charge densities for the anodic peak and the ca-
thodic peak in the absence and presence of copper were cal-
culated from the integration of the voltamograms, and the
values were 31 and −30 mC/cm2 (absence of copper) and
26 and −25 mC/cm2 (presence of copper), respectively. The
2.2. Electrochromic solution and
spectroelectrochemical cell
An aqueous solution with 1.8 × 10−2 mol/L Pb(NO3)2
and 1.0 mol/L NaNO3 in the presence of a desired concen-
tration of Cu(NO3)2·3H2O and ultra pure water was used
throughout the experiments. All chemical products were used
as received. A conventional three-electrode cell set up was
used, consisting of the ITO substrate as working electrode,
a reversible hydrogen electrode as reference electrode and
a platinum auxiliary electrode. Visible and near IR spectra
of the films (350–1500 nm) were recorded in situ with a 5G
model Varian spectrophotometer, by placing the coated sub-
strate in a special electrochemical cell with two flat glass
windows.
2.3. Instrumental measurement techniques
The electrochemical experiments were performed using
an Autolab PGSTAT20, in which the impedance measure-
ments were also realized. Impedance spectra were acquired
using Autolab with a FRA software. The frequency responses
between 100 kHz and 1 mHz were obtained with 5 mV rms
amplitude perturbation.
Fig. 1. Influence of copper on the transmittance response of lead measured
at λ = 633 nm.

C.O. Avellaneda et al. / Electrochimica Acta 50 (2005) 1317–1321
1319
Fig. 2. Cyclic voltammogram for the ITO electrodes in aqueous 1.0 mol/L
NaNO3, 1.8 × 10−2 mol/L Pb(NO3)2 in the absence (—) and presence
(. . .) of cooper (1.84 × 10−3 mol/L Cu(NO3)2·3H2O), potential scan rate of
50 mV/s.
differences between the cathodic and anodic charges may be
due to some lead that remains on the ITO surface or to another
parallel cathodic process, such as the hydrogen evolution re-
action.
The changes of color for the ITO electrode after deposition
of lead in the presence or absence of copper as additive, is
shown in Fig. 3.
The transmittance of the colored and bleached states for
the sample measured at λ = 633 nm without copper were
44 and 85%, respectively. The optical responses with copper
were 10 and 85% for colored/bleached states, respectively.
The lead films, deposited in the presence of Cu2+ in solution,
yields a dark gray color, but that with absence of copper is a
light gray.
The kinetic responses for lead deposited in the presence
and absence of copper were measured at λ = 633 nm during
a potential step at intervals of 60 s between −0.8 V (colored
state) and +0.8 V (bleached state) and are depicted in Fig. 4.
Lead deposition with copper exhibits a significant varia-
tion of transmittance for the coloring/bleaching process (ꢁT
= Tb − Tc = 75%), where Tb and Tc are the transmittances of
bleached and colored processes, respectively, while that with-
out copper leads to a ꢁT = 41% (not shown in the Fig. 4).
The electrodeposition process is slower than electrodissolu-
tion process, where the bleached process takes a few seconds.
The changes of the optical density ꢁOD were calculated
by the equation ꢁOD = log(Tb/Tc), where Tb and Tc is the
transmittance in the bleached and colored processes, respec-
tively (Fig. 5). The optical density calculated at λ = 633 nm
Fig. 3. Transmittance UV–vis-NIR response spectra of ITO in aqueous
1.0 mol/L NaNO3, 1.8 × 10−2 mol/L Pb(NO3)2 (a) absence of copper, (b)
in the presence of copper, colored state (- - -) and bleached state (—).
for the lead deposited in the presence of copper was 0.9,
whereas for the lead deposited in the absence of copper the
value was 0.31.
The impedance response obtained for lead deposited in
the presence of copper was found to depend on the applied
potential. Fig. 6a and b show the Nyquist plot at different

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C.O. Avellaneda et al. / Electrochimica Acta 50 (2005) 1317–1321
Fig. 4. Kinetic responses measured at λ = 630 nm for ITO electrodes in
aqueous 1.0 mol/L NaNO3, 1.8 × 10−2 mol/L Pb(NO3)2, in the presence of
copper (1.84 × 10−3 mol/L Cu(NO3)2·3H2O).
potentials. The impedance diagram measured at E = 0 V ex-
hibits a distorted capacitive semicircle at high frequencies.
It is followed, at intermediate frequencies, by a second con-
tribution related to a diffusion process, which, at the lower
Fig. 6. Nyquist plot measured during lead deposition in presence of copper
(1.84 × 10−3 mol/L Cu(NO3)2·3H2O) at different potentials, (a) E = 0 V
and (b) E = −0.4 V.
frequenciesdeviatesfromadiffusionbehavior, towardsapure
capacitance dynamic response (Fig. 6a). At E = −0.4 V, the
kinetics of the system is almost completely limited by the rate
of the diffusion process. This oxide electroreduction process
takes place simultaneously with the electrochromic change
of the lead-copper deposited film, which changes from being
transparent (oxide state) to gray (reduced state).
4. Conclusions
Fig. 5. Optical density change versus wavelength for the ITO electrodes in
aqueous 1.0 mol/L NaNO3, 1.8 × 10−2 mol/L Pb(NO3)2, in the absence (- -
-) and in the presence (—) of copper (1.84 × 10−3 mol/L Cu(NO3)2·3H2O)
(—).
Electrodeposited films of metallic lead show interest-
ing opto-electrochromic properties. The effect of copper as

C.O. Avellaneda et al. / Electrochimica Acta 50 (2005) 1317–1321
1321
additive produces a higher variation in the optical transmis-
sitivity, with a value as low as 10% for the colored state. This
system may be an interesting technological alternative for
display devices.
[2] P.M.S. Monk, R.J. Mortimer, D.R. Rosseinsky, Electrochromism:
Fundamentals and Applications, Verlag Chemie, Weinhein,
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[3] M.A. Aegerter, “Sol–Gel Chromogenic Materials and Devices” in
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[6] F.H. Smith, British Patent 328017, 1929.
[7] I. Camlibel, S. Singh, H.J. Stocker, L.G. Van Ultert, G.I. Zydzik,
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Acknowledgments
This research was financially supported by the Brazilian
agencies FAPESP, CNPq, FINEP, and PRONEX-FINEP.
[8] S. Zaromb, J. Electrochem. Soc. 109 (1962) 903.
[9] S.C. de Oliveira, L.C. de Morais, A.A.S. Curvelo, R.M. Torresi, J.
Electrochem. Soc. 150 (2003) E578.
[10] S.I. Co´rdoba de Torresi, I.A. Carlos, J. Electroanal. Chem. 414
(1996) 11.
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