An organic aqueous gel as electrolyte for application in electrochromic devices based in bismuth electrodeposition

Article abstract of DOI:10.1149/1.1615610

The purpose of this work was to study the deposition/dissolution behavior of bismuth in an aqueous electrolytic gel media from the point of view of electrochromic phenomena. The gel was made from a derivative polymer of animal protein. This polymer is extremely consistent, and it becomes a transparent gel from 350 to 850 nm (visible region). Moreover, voltammetry and chrono-amperometry experiments have shown that the bismuth deposition/dissolution has excellent electrochemical reversibility with a large variation of transmittance values (around 60%) when Cu²⁺ is added to the gel. It was also shown that copper cations promote Bi/Bi³⁺ reversibility by a redox reaction between Cu²⁺ and metallic bismuth. Thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis were used to verify possible changes in the gel when it was exposed to a heating/cooling cycle. From TG analysis it was possible to verify that degradation of the gel polymer in a large temperature range does not occur and from DSC it was observed that the system only freezes at ca. -35°C.

Full text of DOI:10.1149/1.1615610

E578
Journal of The Electrochemical Society, 150 ͑11͒ E578-E582 ͑2003͒
0
013-4651/2003/150͑11͒/E578/5/$7.00 © The Electrochemical Society, Inc.
An Organic Aqueous Gel as Electrolyte for Application in
Electrochromic Devices Based in Bismuth Electrodeposition
a
a
a
Silvio C. de Oliveira, Lu ´ı s C. de Morais, Antonio Aprigio da Silva Curvelo, and
b, ,z
Roberto M. Torresi *
aInstituto de Qu ´ı mica de S
5513-970 Sao Paulo (SP), Brazil
˜
ao Carlos and Instituto de Qu ´ı mica, Universidade de S
b
˜
ao Paulo,
0
˜
The purpose of this work was to study the deposition/dissolution behavior of bismuth in an aqueous electrolytic gel media from
the point of view of electrochromic phenomena. The gel was made from a derivative polymer of animal protein. This polymer is
extremely consistent, and it becomes a transparent gel from 350 to 850 nm ͑visible region͒. Moreover, voltammetry and chrono-
amperometry experiments have shown that the bismuth deposition/dissolution has excellent electrochemical reversibility with a
2
ϩ
large variation of transmittance values ͑around 60%͒ when Cu is added to the gel. It was also shown that copper cations promote
3
ϩ
2ϩ
Bi/Bi reversibility by a redox reaction between Cu and metallic bismuth. Thermogravimetric ͑TG͒ and differential scanning
calorimetry ͑DSC͒ analysis were used to verify possible changes in the gel when it was exposed to a heating/cooling cycle. From
TG analysis it was possible to verify that degradation of the gel polymer in a large temperature range does not occur and from
DSC it was observed that the system only freezes at ca. Ϫ35°C.
©
2003 The Electrochemical Society. ͓DOI: 10.1149/1.1615610͔ All rights reserved.
Manuscript submitted October 8, 2002; revised manuscript received May 17, 2003. Available electronically September 22, 2003.
Currently there is great interest in the development of optical
The presence of LiBr in the electrolyte avoids the decomposition
Ϫ
devices, mainly those that can control variations of light intensity or
heat. There are about 1800 patents that refer to electrochromic de-
vices, about 1500 are from the Japanese industry, but still there are
great efforts to produce new devices that can exhibit better proper-
of solvent because Br discharge occurs at lower overpotentials than
Ϫ
0
ϭ 1.36 V.13
the Cl /Cl couple, E
ClϪ/Cl2
2
1
4
In a recent work, Ziegler et al. have studied the optical prop-
erties of bismuth reversible electrodeposition aiming its application
at display information devices, using the nonionic polymer, hy-
droxyethylcellulose ͑HEC͒ as the supporting electrolyte which
forms a gel in aqueous media. The main problem concerning this
system is that cellulose and its derivatives suffer hydrolysis in acid
media. The oxygen atom that joins two sugar units is protonated and
a degradation reaction starts from this point resulting in the short-
ening of polymer chains with time. A viscosity diminution is pro-
duced as a consequence of this reaction, and the properties of the
1
2
ties. Display information devices, automotive applications, and
windows, which can control the sunray intensity were the first elec-
trochromic products commercialized.
Devices based in metal deposition contain the electrochromic
material in the electrolyte that, by the passage of electric current,
3
produce a thin film on the substrate. This device uses the reversible
electrodeposition to produce an optical modulation, which does not
involve ion insertion, as in the case of WO , and was first proposed
3
4
5
6-8
by Smith in 1929. Some years later, Camlibel and Zaromb re-
lated the reversible electrodeposition of silver to optical modulation.
Recently, similar devices have been proposed to be used in different
aqueous or nonaqueous media; one of these devices based on lead
15
16
polymer are modified. There is also a patent where several
acrylic and cellulose resins are proposed in order to make aqueous
gels with different metal cations salts.
9
electrodeposition in aqueous media shows a transmittance variation
One problem that must be overcome to make reversible elec-
trodeposition electrochromic device in an aqueous media is to find
an ideal electrolytic system with gel properties, such as transpar-
ency, good conductivity, reversibility, and stability in acid media and
in a wide range of temperature close to 25°C. While the device can
be built using a liquid electrolyte, the use of a stiffener electrolyte
can facilitate its construction, minimizing electrolyte leakage that
may affect the device performance or create a chemical safety haz-
ard. The use of a stiffener electrolyte also produces a diminution of
the sensitivity to atmospheric contaminants, and it can avoid the
necessity of a leak-tight seal. However, such electrolytes have a
limited range of working temperature and a narrow voltage operat-
ing range compared with organic-based electrolytes with high boil-
ing point solvents.
of ca. 60%. The main problem is that a high amount of charge ͑185
Ϫ2
mC cm ͒ is necessary to produce lead electrodeposition in the pres-
ence of Cu2 as additive. Another device uses copper salt in an
ϩ
ammoniac media as an electrochromic electrolyte; the principle of
2
ϩ
0
operation of this device is the reduction of Cu to Cu in the
ϩ
2ϩ
transparent cathode while Cu is oxidized to Cu in the transparent
1
0
anode.
Recent studies with metallic bismuth1
1,12
have been done by Zie-
gler et al., and they have shown a very promising electrochromic
3
device, which is based on the deposition and dissolution properties
3
ϩ
of metallic bismuth in aqueous media. The device contains Bi and
Ϫ
2ϩ
Br and small amounts of Cu as an additive. The potential re-
quired for the redox process is low, about 1–2 V dc, and the charge
Ϫ2
required is around 10 mC cm to produce a deep transmittance
change.
The aim of this work is to study the impact of a new organic gel
electrolyte, based in an animal protein, on the electrochromic effect
of bismuth and the gel stability. The use of animal protein to make
the electrolytic gel is an original approach of this work, that to the
best of our knowledge has never been proposed before in patents or
The global reaction that occurs in the working electrode can be
described as:
Ϫ
Ϫ
0
Ϫ
BiCl4 ϩ 3e → Bi ϩ 4Cl
E ϭ ϩ0.16 V
0
͓1͔
1
4,16
Ϫ
published papers.
Also, a detailed mechanism, based in experi-
with the corresponding discharge of Br on the counter electrode,
according to
2
ϩ
mental evidence, to explain the effect of Cu on the improvement
of bismuth dissolution is proposed. This study was performed using
thermal analysis, cycling voltammetry, chronoamperometry, and
chromogenic analysis. Gelatin was chosen to form the gel system
and, because it is a material used in the food industry, it is inexpen-
sive, nontoxic, and it can be used to prepare transparent solutions
with high viscosity.
Ϫ
Ϫ
Ϫ
3
Br → Br3 ϩ 2e
E ϭ Ϫ1.09 V
0
͓2͔
*
Electrochemical Society Active Member.
E-mail: rtorresi@iq.usp.br
z

Journal of The Electrochemical Society, 150 ͑11͒ E578-E582 ͑2003͒
E579
Figure 2. TGA experiments of different aqueous gel electrolytes: ͑᭝͒ pure
gelatin, ͑᭡͒ Bi5Cu2, ͑᭹͒ Cu10, ͑᭺͒ Bi5Cu5, ͑᭿͒ Bi5, ͑ᮀ͒ gelHCl, and ͑᭢͒
Bi5Cu10.
PDA1 photodiode amplifier ͑WPI, Inc.͒ designed for low light level
detection with a current resolution of typically 1 pA. The output
signal of PDA1 was delivered to the analogical input of the poten-
tiostat and both current and transmittance were collected simulta-
neously. Differential scanning calorimetry ͑DSC͒ and thermogravi-
metric analysis ͑TGA͒ were performed using a Shimadzu-50
instrument. DSC experiments were carried out from Ϫ70 to 200°C
and TGA from room temperature, 25°C, to 200°C at a heating rate
of 5°C/min.
Figure 1. ͑a͒ Basic design of electrochromic device: 1, Teflon lid; 2, Teflon
spacer; 3, working electrode ͑ITO͒; 4, reference electrode ͑Ag/AgCl͒; 5,
counter electrode ͑platinum sheet͒; 6, glass window; 7, Teflon box; 8, as-
sembled electrochromic device. ͑b͒ Transparent gel made after mixture of
electrolytes.
Experimental
Results and Discussion
Electrolytic solutions were prepared using reagent grade bis-
muth͑III͒ chloride and copper͑II͒ chloride ͑Aldrich͒. Water was pu-
rified with Millipore Milli-Ro plus system. To prepare the gel sys-
tem 1.5 g of animal protein ͑Oetker™͒ was dissolved in 3.5 mL of
water and heated at 50°C under stirring. Then, 4.0 mL of
Thermal analysis.—Figure 2 shows TGA experiments for all
samples used in this work. As can be observed, samples with HCl,
bismuth, and copper salts show a greater mass loss than the pure
protein from 25 to 200°C. This is consistent with the fact that it used
water and aqueous-saline solution to prepare the gels. However, gels
exhibit different behavior during heating, in spite of being prepared
using the same amount of water, except in the case of gelHCl. The
sample Bi5Cu2 exhibits the highest thermal stability followed by
Cu10. It means that the discrepancy that was observed depends on
the amount and the nature of ion in the gel. The presence of these
electrolytes can trap the liquid inside the gel in different ways and
thus, responses in the thermal effects can be also different.
3
ϩ
ϩ
2ϩ
Bi /H /Cu solution was added and maintained under stirring for
5 min. The solutions prepared were identified as gelHCl
HCl 500 mM ϩ protein), Bi5 (BiCl 5 mM ϩ HCl 500 mM
(BiCl 5 mM ϩ CuCl 2 mM ϩ HCl
1
(
3
ϩ protein),
Bi5Cu2
3
2
5
00 mM ϩ protein), Bi5Cu5 (BiCl 5 mM ϩ CuCl 5 mM ϩ
3 2
HCl 500 mM ϩ protein); Bi5Cu10 (BiCl 5 mM ϩ CuCl 10 mM
3
2
ϩ HCl 500 mM ϩ protein); Cu10 (CuCl 10 mM ϩ HCl 500 mM
2
ϩ protein).
In order to better understand the thermal behavior of the gel
some DSC experiments were run. Figure 3 shows experiments for
different gels when they were frozen from room temperature to
Ϫ70°C. Between Ϫ30 and Ϫ40°C an exothermic peak is observed,
and it corresponds to the freezing point of the system. The tempera-
ture transition becomes more negative for gels containing HCl and
salts than the pure gelatin. This fact clearly shows that both water
and electrolytes interact with the protein in different ways, depend-
ing on the kind and amount of ions. If the temperature transition
depends only on ion concentration, the most negative temperature
should be for the Bi5Cu5 sample, but this is not the case, and the
sample Bi5Cu2 exhibits the most negative transition temperature.
When samples are heated from Ϫ70 to 200°C ͑Fig. 4͒, two endo-
thermic processes are observed. The former at ca. Ϫ7°C corre-
sponds to the melting processes of free water present in the system.
The characteristic temperature of this process is more negative for
gel ϩ HCl ϩ salt system than for the gel with pure protein
Figure 1a shows a schematic representation of the electrochemi-
cal cell used in the experiment. A Teflon support with the gel elec-
trolyte was sandwiched between a working electrode of indium tin
oxide ͑ITO, Delta Technologies͒, with a nominal sheet resistance of
2
20 ⍀/ᮀ and a geometrical area of 0.3 cm and a Pt sheet as counter
2
electrode ͑5 cm of geometrical area͒ with a 0.6 cm diam orifice to
allow light transmission. The three-electrode system incorporated a
Ϫ
Ag/AgCl/Cl electrode as reference. Figure 1b shows a picture of
the gel made from Bi5Cu5 solution where is possible to note its
transparency and firmness.
Voltammetric and chronoamperometric measurements were per-
formed using an AUTOLAB PGSTAT30 potentiostat/galvanostat
͑
Ecochimie͒ in a three-electrode configuration. Chromogenic analy-
ses were made simultaneously with voltammetric experiments using
a solid-state light source ͑WPI, Inc.͒. Plastic fiber optic cables up to
1
mm in diameter were used to deliver light from the device to a

E580
Journal of The Electrochemical Society, 150 ͑11͒ E578-E582 ͑2003͒
Figure 3. DSC ͑normalized curves͒ of different aqueous-gel electrolyte dur-
ing cooling. ͑ᮀ͒ GelHCl, ͑᭿͒ Bi5, ͑᭹͒ Cu10, ͑᭡͒ Bi5Cu2, ͑᭺͒ Bi5Cu5, and
͑᭢͒ Bi5Cu10.
ϩ HCl, showing that the presence of the inorganic compound pro-
duces an increase in the interaction between water and the polymeric
network. The other endothermic process ͑at ϳ60°C͒ corresponds to
the loss of conformation, helix-coil transition.17 This transition be-
gins around 40°C, and it is the same temperature that the loss of
water was observed from TGA experiment. This suggests that, when
the helix-coil transition happens the water that was trapped by poly-
meric network is released, thus a smaller energy is required. These
preliminary results are important in order to show that this system
can be used in an electrochromic device due to its thermal stability
up to 200°C in a close system.
Figure 5. Potentiodynamic of j/E ͑
͒ and A/E ͑᭹͒ profiles at 10 mV
Ϫ1
s
: ͑a͒ Bi5 and ͑b͒ Cu2 gel solutions.
gel electrolyte reordered at 10 mV sϪ1; the change in absorbance
obtained simultaneously with the potentiodynamic experiment is
also depicted. Figure 5a shows that the modulation of the device
transparency depends on the applied potential; the device being in
the transparent state at positive potentials, because there is no bis-
muth electrodeposition and the gel does not adsorb the light. Scan-
ning in the negative direction, a sharp cathodic writing threshold
peak is evident at approximately Ϫ0.42 V, and it corresponds to
Chromogenic characterization.—Figure 5 shows cyclic voltam-
mograms of bismuth ͑a͒ and copper ͑b͒ electrodeposition in aqueous
3
ϩ
Bi ion reduction. So, once the cell was polarized at approximately
Ϫ0.25 V, the darkening of the electrode as a result of bismuth depo-
sition is clearly seen in a few seconds. Under these conditions, and
in the visible region, the absorbance drastically came up. If the
plating voltage persists the bismuth deposit becomes thicker and the
working electrode becomes increasingly dark until it eventually ap-
pears black. The gray shade control is obtained via the reduction
0
charge consumed at the working electrode. After Bi deposition, and
scanning in the positive direction, bismuth oxidation takes place
͑potential peak at Ϫ0.075 V͒, but the absorbance of the cell does not
drop. In other words, bismuth does not totally dissolve from the
electrode. This is strong evidence of the high irreversibility of the
bismuth deposition/dissolution reaction. It is well known that Cu2
is often used as an additive to improve bismuth reversibility. Figure
ϩ
5b shows the copper voltammogram and absorbance/E curves. Scan-
ning in the negative direction, a current peak appears at ca. Ϫ0.26 V,
2
ϩ
1ϩ
which corresponds to the reduction of Cu to Cu and, as can be
seen, absorbance does not change indicating that this redox reaction
does not produce copper deposition and confirming that this process
corresponds to Cu reduction to Cu . At more negative poten-
tials, a current increase is seen, which corresponds to copper depo-
Figure 4. DSC ͑normalized curves͒ of different aqueous-gel electrolyte dur-
ing heating. ͑ᮀ͒ GelHCl, ͑᭿͒ Bi5, ͑᭹͒ Cu10, ͑᭡͒ Bi5Cu2, ͑᭺͒ Bi5Cu5, and
2
ϩ
1ϩ
͑᭢͒ Bi5Cu10.

Journal of The Electrochemical Society, 150 ͑11͒ E578-E582 ͑2003͒
E581
negative direction, the bismuth deposition wave appears, but it is
2
ϩ
1ϩ
also observed the Cu /Cu reaction in the 0.05 and Ϫ0.20 V
potential range. During the positive-going potential, there are two
0
0
current peaks, corresponding to Bi oxidation ͑Ϫ0.070 V͒ and Cu
to Cu
2
ϩ
oxidation process ͑0.60 V͒. The A/E potentiodynamic
curves clearly show the reversibility of the deposition/dissolution
process, showing in the positive-going potential a decrease between
0
Ϫ0.20 and 0 V associated to the oxidation process of Bi and an-
other important decrease between 0.40 and 0.75 V associated with
copper oxidation.
The nature of the effect of copper on bismuth reversibility is not
so clear, but it has been already pointed out in the literature18 that
some species can catalyze or inhibit the electrodeposition process.
One way in which these species behave as inhibitors is by producing
the redissolution of the deposits, consequently leading to substantial
transformation of film morphology ͑i.e., avoiding the formation of
dendrites or pores͒ and producing a change of the tridimensional
growth into a bidimensional one. From X-ray photoelectric spectros-
copy ͑XPS͒ and secondary ion mass spectrometry ͑SIMS͒ studies,14
it was found that copper does not adsorb simultaneously with bis-
muth on the transparent conductive electrode surface. Furthermore,
while copper codeposition was evident in thin films grown from
electrolytes containing bismuth and copper, it does not deposit at
underpotential conditions simultaneously with bismuth, nor form bi-
1
9
nary alloys with bismuth. Thus the increasing of redissolution of
the deposits are directly related to the redox process that occurs
between bismuth and copper. It is possible to describe the deposition
2
ϩ
process as follows: from 0 to Ϫ0.20 V, the first reduction of Cu
Ϫ
2ϩ
1ϩ
occurs (1e ϩ Cu → Cu ) and at more negative potentials, bis-
Ϫ
3ϩ
0
muth and copper codeposition begins (3e ϩ Bi → Bi and
Ϫ
2ϩ
0
2
e
ϩ Cu → Cu ). During the positive-going potential, the
stripping of the metallic deposit shows two main current peaks,
which correspond to a two-stage oxidation process. The one occur-
0
3ϩ
ring at the more negative potential can be associated to Bi /Bi and
Cu /Cu oxidation processes, but Cu is a thermodynamically
unstable intermediate, and as a consequence, Cu tends to rapidly
disproportionate to Cu and Cu . Finally, the current peak at more
0
1ϩ
1ϩ
2
0
ϩ
Figure 6. Potentiodynamic of j/E ͑
͒ and A/E ͑᭹͒ profiles at 10 mV
0
2ϩ
Ϫ1
s
: ͑a͒ Bi5Cu2 and ͑b͒ Bi5Cu5 gel solutions.
0
2ϩ
positive potentials is related to the oxidation of Cu /Cu
.
Moreover, to better understand the copper influence on stripping
the remaining bismuth onto ITO, a sequence of alternated voltam-
metry and chronopotentiometry experiments in the presence and ab-
2
ϩ
sence of Cu in an acid aqueous bismuth solution ͑not gel͒ were
sition from Cu2 , leading to a small increase in absorbance. Scan-
ning in the positive direction, it is possible to see a cathodic current
until ca. Ϫ0.20 V due to copper deposition, which is corroborated
by the increase of absorbance until Ϫ0.27 V. At more positive po-
ϩ
run. Figure 7a shows the potential/time program used and the po-
2
ϩ
tential where the solution of Cu was added. Beginning with a
linear negative-going potential from 1.0 down to Ϫ0.55 V, this po-
tential was held for 90 s in order to produce a thick bismuth film
layer. After that, a positive-going potential was applied until the
potential where Cu was added ͑Ϫ0.30 or 0.60 V͒. These poten-
tials were held for 120 s and after that a ramp was applied until the
final potential ͑1.0 V͒ was reached. Comparing charge and absor-
bance it was possible to understand the influence of copper on bis-
muth dissolution. Figure 7b and c show q/t and A/t profiles for two
different potential values where Cu was added, Ϫ0.30 V ͑Fig. 7b͒
and 0.60 V ͑Fig. 7c͒, respectively. For both experiments the depo-
sition and dissolution charges are the same only when Cu2 is
added, and this reversibility is confirmed by the absorbance profile.
When copper is added at Ϫ0.30 V, it produces an increase of absor-
bance ͑Fig. 7b͒ because at this potential there is some copper depo-
sition. However, after the addition, there is a complete dissolution of
the deposit. Even when copper is added at 0.60 V, where there is no
copper deposition or Cu formation, the effect is similar to that
observed at Ϫ0.30 V. This experiment clearly shows that there is a
redox reaction between Cu and Bi producing the oxidation of Bi
to Bi and the reduction of Cu to Cu , which is reoxidized at
more positive potentials than 0.30 V. This redox reaction allows the
dissolution of metallic bismuth that is due to its dendritic forms
loose electric contact with the substrate. This reaction produces a
0
tentials, Cu dissolution becomes important, and a diminution of
absorbance and a current peak at Ϫ0.15 V are observed, which
corresponds to the oxidation of Cu to Cu . A second oxidation
process is observed at 0.56 V, which corresponds to Cu to Cu
2
ϩ
0
1ϩ
0
2ϩ
reaction, and it is accompanied by a diminution of absorbance. This
experiment clearly shows the excellent reversibility of copper,
which is a very interesting electrochromic characteristic, but the
problem is that, in the case of copper deposition, it is necessary to
apply more negative potentials ͑Ϫ0.60 V͒ and the absorbance varia-
tion is smaller than in the case of bismuth deposition.
Figure 6a and b shows j/E and A/E potentiodynamic profiles of
bismuth aqueous gel in the presence of two different copper concen-
trations, 2 mM ͑Bi5Cu2͒ and 5 mM ͑Bi5Cu5͒, respectively. It can be
seen that the deposition overpotential in both cases is the same ͑ca.
Ϫ0.20 V͒, and it is independent of copper concentration. The pres-
ence of copper increases the absorbance intensity because of bis-
muth and copper codeposition. Moreover, the more important fact
that must be pointed out is the considerable increase in the revers-
ibility of the bismuth deposition/dissolution process. These results
obtained in a gel media reveal many similarities ͑like potential
range, deposition/dissolution charges͒ with experiments performed
in aqueous12 and hydroxyethylcellulose media. Scanning in the
2
ϩ
ϩ
1
ϩ
2
ϩ
0
0
3
ϩ
2ϩ
0
14

E582
Journal of The Electrochemical Society, 150 ͑11͒ E578-E582 ͑2003͒
cal dissolution of Bi and the deposition of metallic copper, which is
2
ϩ
easily oxidized to Cu at more positive potentials than 0.30 V.
3
ϩ
2ϩ
Finally, the combination of the two cations, Bi and Cu in aque-
ous acid media, allows the preparation of transparent gel solutions,
which can give reversible electrodeposits due to the chemical redox
2
ϩ
reaction between metallic bismuth and Cu
.
Conclusions
The gel formed from solutions containing bismuth and copper
cations exhibits a greater mass loss than pure protein due to water
coordination with the acid and salts added to the protein. DSC ex-
periments show that ions and water interact with the protein and
only water evaporation is observed until 200°C ͑endothermic pro-
cesses͒, corroborating that there is no gel decomposition.
Electrochemical experiments allow the verification that the re-
versibility of bismuth deposition/dissolution is improved by the ad-
dition of copper cations to the gel solution. The role played by
copper on the bismuth reversible electrodeposition system was
clearly determined to be a redox reaction between Cu and Bi0
2ϩ
0
leading to the dissolution of Bi with poor electric contact due to the
0
dendritic deposit and to the formation of a Cu deposit, which is
dissolved at positive potentials greater than 0.30 V.
Acknowledgments
The authors thank CNPq and FAPESP ͑Brazilian agencies͒ for
the financial support. S. C. O. and L. C. M. thank CNPq ͑no.
140505/1999-7͒ and FAPESP ͑no. 98/15734-8͒ respectively, for
scholarships.
S
˜
ao Paulo State Foundation (FAPESP) assisted in meeting the publica-
tion costs of this article.
References
1
2
. J. P. Coleman, A. T. Lynch, P. Madhukar, and J. H. Wagenknecht, Sol. Energy
Mater. Sol. Cells, 56, 395 ͑1999͒.
. C. Bechinger, J. N. Bullock, J. G. Zhang, C. E. Tracy, D. K. Benson, S. K. Deb, and
H. M. Branz, J. Appl. Phys., 80, 1226 ͑1996͒.
3
4
5
. J. P. Ziegler, Sol. Energy Mater. Sol. Cells, 56, 477 ͑1999͒.
. F. H. Smith, Br. Pat. 328,017 ͑1929͒.
. I. Camlibel, S. Singh, H. J. Stocker, L. G. Van Ultert, and J. Zydzik, Appl. Phys.
Lett., 33, 793 ͑1978͒.
6
7
8
9
. S. Zaromb, J. Electrochem. Soc., 109, 903 ͑1962͒.
. S. Zaromb, J. Electrochem. Soc., 109, 912 ͑1962͒.
. J. Mantell and S. Zaromb, J. Electrochem. Soc., 109, 992 ͑1962͒.
. L. H. Mascaro, E. K. Kaibara, and L. O. S. Bulh
L273 ͑1997͒.
˜
oes, J. Electrochem. Soc., 144,
1
0. M. Herlem, M. Sz e´ kely, E. Sutter, C. Mathieu, A. M. Gon c¸ alves, E. Caillot, G.
Figure 7. ͑a͒ Potential/time program applied. v ϭ 10 mV/s. ͑b͒ q/t
2
ϩ
Herlem, and B. Fahys, Electrochim. Acta, 46, 2967 ͑2001͒.
1. S. C. Oliveira, R. M. Torresi, and S. I. C o´ rdoba de Torresi, Quim. Nova, 23, 79
͑
͑
͑
͑
—᭹—᭹—͒ and A/t ͑—᭿—᭿—͒ without addition of Cu
.
q/t
1
—᭺—᭺—͒ and A/t ͑—ᮀ—ᮀ—͒ with addition of Cu2 at Ϫ0.30 V.
ϩ
͑
2000͒.
2
ϩ
c͒ q/t ͑—᭹—᭹—͒ and A/t ͑—᭿—᭿—͒ without addition of Cu . q/t
12. S. I. C o´ rdoba de Torresi and I. A. Carlos, J. Electroanal. Chem., 414, 11 ͑1996͒.
13. CRC Handbook of Chemistry and Physics, 76th ed., D. R. Lide and H. P. R.
Frederikse, Editors, pp. 8-21, CRC Press, Boca Raton, FL ͑1995͒.
2
ϩ
—᭺—᭺—͒ and A/t ͑—ᮀ—ᮀ—͒ with addition of Cu at 0.60 V.
1
1
4. B. Howard and J. P. Ziegler, Sol. Energy Mater. Sol. Cells, 39, 309 ͑1995͒.
5. D. Fengel and G. Wegner, Wood Chemistry, Ultrastructure and Reactions, p. 268,
Walter de Gruyter & Co, Berlin ͑1989͒.
new metallic copper deposit that is easily removed at more positive
potentials than 0.30 V. So that, when metallic bismuth is deposited
1
6. B. Warszawski, U.S. Pat. 5,056,899 ͑1990͒.
17. P. J. A. Sobral and A. M. Q. B. Habitante, Food Hydrocolloids, 15, 377 ͑2001͒.
18. V. Jirincny, H. Choi, and J. W. Evans, J. Appl. Electrochem., 17, 91 ͑1987͒.
19. J. Wang, J. Lu, U. A. Kirg o¨ s, S. B. Hocevar, and B. Ogorevc, Anal. Chim. Acta,
0
0
in the presence of copper, a codeposit of Bi and Cu is formed.
¨
When this codeposit is oxidized, Bi3 and Cu are produced and
ϩ
2ϩ
4
34, 29 ͑2001͒.
the latter suffers a redox reaction with the metallic bismuth that was
not dissolved due to the poor electric contact, producing the chemi-
2
0. U. Bertocci and D. R. Turner, Encyclopedia of Electrochemistry of the Elements,
Vol. 2, A. J. Bard, Editor, p. 384, Marcel Dekker, New York ͑1974͒.