Electrochemical study of copper in the 1-ethyl-3-methylimidazolium dicyanamide room temperature ionic liquid

Article abstract of DOI:10.1149/1.2840627

The potential utility of the air- and water-stable ionic liquid 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA) for electrochemical application was evaluated with copper(I) chloride. The temperature dependency of the density and absolute viscosity of EMI-DCA were measured over a temperature range from 297 to 343 K, and equations describing the dependencies are presented. Due to the ligand property of the DCA anion, both CuCl and CuCl2 are soluble in EMI-DCA. Cyclic voltammograms of Cu(I) in EMI-DCA and other two ionic liquids were compared. Cu(I) can be oxidized to Cu(II) or reduced to Cu metal in these solutions. The electrodeposition of Cu on glassy carbon and nickel electrodes involves a three-dimensional progressive nucleation and growth process. Scanning electron microscopy and X-ray diffraction results indicate that the morphology of the copper electrodeposits is dependent on the deposition potential, and compact coatings containing nanocrystalline copper could be obtained by potentiostatic electrolysis at low overpotentials. The low viscosity of EMI-DCA and the high solubility of metal chlorides in it would facilitate the electrodeposition of metals using this ionic liquid.

Full text of DOI:10.1149/1.2840627

Journal of The Electrochemical Society, 155 ͑4͒ F55-F60 ͑2008͒
F55
0013-4651/2008/155͑4͒/F55/6/$23.00 © The Electrochemical Society
Electrochemical Study of Copper in the
1-Ethyl-3-Methylimidazolium Dicyanamide
Room Temperature Ionic Liquid
,z
Tin-Iao Leong,a I-Wen Sun,a, Ming-Jay Deng,a Chi-Ming Wu,a and
*
Po-Yu Chenb,
*
aDepartment of Chemistry, National Cheng Kung University, Tainan, Taiwan
bFaculty of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung, Taiwan
The potential utility of the air- and water-stable ionic liquid 1-ethyl-3-methylimidazolium dicyanamide ͑EMI–DCA͒ for electro-
chemical application was evaluated with copper͑I͒ chloride. The temperature dependency of the density and absolute viscosity of
EMI–DCA were measured over a temperature range from 297 to 343 K, and equations describing the dependencies are presented.
Due to the ligand property of the DCA anion, both CuCl and CuCl2 are soluble in EMI–DCA. Cyclic voltammograms of Cu͑I͒ in
EMI–DCA and other two ionic liquids were compared. Cu͑I͒ can be oxidized to Cu͑II͒ or reduced to Cu metal in these solutions.
The electrodeposition of Cu on glassy carbon and nickel electrodes involves a three-dimensional progressive nucleation and
growth process. Scanning electron microscopy and X-ray diffraction results indicate that the morphology of the copper electrode-
posits is dependent on the deposition potential, and compact coatings containing nanocrystalline copper could be obtained by
potentiostatic electrolysis at low overpotentials. The low viscosity of EMI–DCA and the high solubility of metal chlorides in it
would facilitate the electrodeposition of metals using this ionic liquid.
© 2008 The Electrochemical Society. ͓DOI: 10.1149/1.2840627͔ All rights reserved.
Manuscript submitted December 4, 2007; revised manuscript received January 11, 2008. Available electronically March 3, 2008.
Room temperature ionic liquids ͑ILs͒ obtained from the combi-
nation of anhydrous aluminum chloride and 1-ethyl-3-
methylimidazolium chloride ͑EMIC͒1 have been extensively studied
as the electrolytes for various electrochemical applications such as
high-efficiency batteries and electroplating. Numerous examples on
the use of chloroaluminate ILs for the electrodeposition of single
metals and alloys have been reported.2 Their high moisture sensitiv-
ity, however, may complicate the incorporation of these ILs into
commercial devices. The applications of the ILs has been greatly
accelerated by the discovery of the landmark air- and water-stable
ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate
͑EMI–BF4͒,3 1-butyl-3-methylimidazolium tetrafluoroborate ͑BMI–
BF4͒,4 and 1-butyl-1-methylpyrrolidinium bis͑trifluoromethylsulfo-
nyl͒amide ͑BMP–TFSI͒.5 New ILs have been continuously devel-
oped and studied since then.6-8 Ionic liquids such as EMI–BF4 IL
was obtained by combining equal molar quantities of EMI+ and
BF−4. In other words, it can be considered as a neutral IL. It was
found, however, that many metal compounds or metal chlorides do
not dissolve well in the neutral IL. From a practical point of view, it
is of great interest to search for ILs with good solubility, low cost,
low viscosity, and a wide potential window.
Recently, low-viscosity ILs based on the dicyanamide ͑DCA͒
anion have been synthesized and characterized. Due to the donor
ligand property that is known for the dicyanamide anions,9-12 many
metal compounds are expected to be soluble in the DCA-based ILs
by complexing with DCA anions. This feature would make it easier
to prepare a bath solution for electrodeposition.
The electrochemistry of copper species has been studied in sev-
eral ionic liquids. In the Lewis acidic and basic chloroaluminates,
anodic dissolution of copper produces Cu͑I͒, which can be reduced
to Cu metal.13,14 CuCl is insoluble in the EMI–BF4 IL but was made
soluble when excess chloride ions were introduced to form the
chloride-rich IL ͑denoted as EMI–Cl–BF4͒, and Cu metal was ob-
tained by the reduction of the Cu͑I͒.15 Cu͑II͒ was studied in a
CuCl is insoluble in the 1-butyl-3-methylimidazolium hexafluoro-
phosphate ͑BMI–PF6͒ IL. However, copper nanoparticles were elec-
trodeposited by direct electrochemical reduction of the CuCl pow-
ders attached to the electrode substrate.19
Although the DCA-based ILs may be a promising electrolyte for
the electrodeposition of metals, there is a paucity in the literature
regarding the electrodeposition of metals in this IL system. To ex-
plore the utility of this IL system, 1-ethyl-3-methylimidazolium di-
cyanamide ͑EMI–DCA͒ ͑Scheme 1͒ was synthesized and employed
for the electrochemistry and electrodeposition of copper in this
work. Both CuCl and CuCl2 are soluble in the EMI–DCA.
Experimental
Apparatus and chemicals.— The EMI–DCA IL was prepared
and purified following the previous literature;12 however, chloroet-
hane rather than iodoethane was used in this study. All electrochemi-
cal experiments were performed under a purified nitrogen atmo-
sphere in a glove box ͑Vacuum Atmospheres Co.͒, where both the
moisture and oxygen contents were maintained below 1 ppm. An-
hydrous CuCl and CuCl2 ͑99.999%, Strem͒ were used as received.
All electrochemical experiments were carried out with an EG&G
PARC model 273A potentiostat/galvanostat controlled by EG&G
model 270 software. Experiments were performed in a three-
electrode cell. For cyclic voltammetry, the working electrodes were
a platinum electrode, a nickel electrode, or a glassy carbon elec-
trode. A platinum wire ͑Alfa Aesar, 99.95%͒ immersed in ferrocene/
ferrocenium ͑Fc/Fc+ = 50/50 mol %͒ BMP–TFSI solution con-
tained in a glass tube with a porous Vycor tip ͑Bioanalytical
Systems, MF-2042͒ was used as a reference electrode; therefore, all
the potentials reported in this paper are with respect to this refer-
ence. The counter electrode was a spiral copper wire which was
immersed in the bulk ionic liquid solution. Electrodeposition experi-
ments were conducted on nickel wires.
trimethyl-n-hexylammonium
bis͑trifluoromethyl͒sulfonyl͒amide
͑TMHA–TFSI͒ IL using the divalent copper salt, Cu͑TFSI͒2, as the
Cu͑II͒ source.16,17 The solubility of CuCl in 1-butyl-1-
methylpyrrolidinium bis͑trifluoromethylsulfonyl͒amide ͑BMP–
TFSI͒ IL is very limited, and the Cu͑I͒ was produced by anodic
dissolution of a copper electrode for the deposition study.18 The
*
Electrochemical Society Active Member.
z E-mail: iwsun@mail.ncku.edu.tw
Scheme 1. Chemical formula of EMI–DCA ionic liquid.
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Journal of The Electrochemical Society, 155 ͑4͒ F55-F60 ͑2008͒
Table I. Physical properties of the selected room temperature
ionic liquids.
Composition
␳ ͑g/cm3͒
␩ ͑cP͒
Reference
EMI–DCA
EMI–BF4
1.064͑297 K͒
1.240͑295 K͒
1.2553͑303K͒
1.520͑295 K͒
1.38͑298 K͒
1.285͑295 K͒
1.6͑295 K͒
1.29͑298 K͒
1.429͑292 K͒
1.170͑303 K͒
1.370͑303 K͒
1.379͑301 K͒
22.7͑297 K͒
37.7͑295 K͒
48.8͑303 K͒
34.0͑295 K͒
45͑290 K͒
35͑298 K͒
61͑299 K͒
17͑298 K͒
52.0͑293 K͒
233͑303 K͒
312͑303 K͒
67.2͑301 K͒
This study
26
15
26
27
EMI–Cl–BF4
EMI–TFSI
EMI–TfOa
EMI–TfAa
EMI–BETIa
EMI–AlCl4
BMI–TFSI
BMI–BF4
27
27 and 28
29
26
26
26
22
BMI–PF6
BMP–TFSI
a TfO = CF3SO3, BETI = C4F10NO4S2, TfA = CF3CO2.
the linear relationship between ln ␩ and 1/T. A linear equation of
the form
ln ␩ = y0 + y1͑103 ϫ 1/T͒
͓3͔
where ln ␩ and 103 ϫ 1/T, was fitted to the experimental data by
using linear regression techniques. The fitted values of y0 and y1
were −6.0374 and 2.7076, respectively, within a temperature range
from 297 to 343 K.
Table I compares the absolute viscosity and density for some
selected room temperature ILs. As can be seen, the viscosity of
EMI–DCA is relatively low and comparable to the alkyl-substituted
imidazolium-based ionic liquids that employ BF−4, PF6−, and TFSI−
as the anions. Although the charge in the DCA anion was mainly
centered on the amide nitrogen, delocalization across the whole mol-
ecule is likely, and it is expected to produce a weak ion–ion inter-
action, which is important for producing ILs with a low melting
point and low viscosity.12 The much lower viscosity of EMI–DCA
IL implies a more efficient mass transport and higher conductivity.
Figure 1. ͑Color online͒ ͑a͒ Density of EMI–DCA as a function of tempera-
ture. ͑b͒ Relationship between the viscosity of EMI–DCA and temperature.
The surface morphology and elemental composition of the cop-
per coatings were investigated with the Philip XL-40FEG field-
emission scanning electron microscope ͑SEM͒ and its auxiliary
X-ray energy-dispersive spectroscope ͑EDS͒. The crystal structure
of the copper coatings was also analyzed by the Rigaku D/MAX
2500 diffractometer.
Voltammetric studies.— Figure 2 shows the electrochemical win-
dow expressed by linear scan voltammograms of the neat EMI–
DCA, EMI–TFSI, and EMI–Cl–BF4 recorded at a glassy carbon
electrode. Because the cathodic limit of the ionic liquids is due to
the reduction of the EMI+ cation, all three ILs exhibit a similar
cathodic limit near −2.4 V. The anodic limit of the ionic liquids is
determined by the electrochemical oxidation of the DCA−, TFSI−,
and Cl−, respectively. The EMI–DCA exhibits an anodic limit near
Measurements of density and viscosity.— Density and viscosity
measurements were carried out over a temperature range from 297
to 343 K with a calibrated Pyrex glass dilatometer and an Ostwald
viscometer, respectively. The detailed description of the construction
of the dilatometer and viscometer, as well as the procedures for the
measurements, has been reported elsewhere.20,21
Results and Discussion
The temperature dependence of the selected physical properties
of EMI–DCA.— The ionic liquid used for physical property mea-
surements was dried under vacuum at 393 K for 24 h before use; the
dilatometer and viscometer had to be airtight. The experimental den-
sity data for the EMI–DCA ionic liquid displayed a linear depen-
dence on the absolute temperature as shown in Fig. 1a. By using
linear regression techniques, the experimental data were fitted to a
linear equation of the form
␳ = x0 + x1T
͓1͔
where ␳ is the density and T is the absolute temperature. The fitted
values of the coefficients x0 and x1 were found to be 1.5431 and
−0.0016, respectively, over a temperature range from 297 to 343 K.
The values of the experimental kinematic viscosity, ␯, measured
with the viscometer described above, were converted to dynamic or
absolute viscosities, ␩, by
␩ = ␳␯
͓2͔
An Arrhenius plot of ln ␩ vs 1/T was constructed from the experi-
mental data and linearity was obeyed. This linear behavior has also
been reported recently;22 the viscosity of EMI–DCA was measured
over the temperature range from 297 to 343 K. Figure 1b represents
Figure 2. Staircase linear scan voltammograms recorded at a GC electrode
at 313 K for ͑A͒ EMI–DCA, ͑B͒ EMI–Cl–BF4, and ͑C͒ EMI–TFSI melts.
The scan rate was 50 mV s−1
.
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Journal of The Electrochemical Society, 155 ͑4͒ F55-F60 ͑2008͒
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Figure 3. Staircase cyclic voltammograms recorded at a Pt electrode at 313
K for 50 mM Cu͑I͒ in ͑A͒ EMI–DCA, ͑B͒ EMI–Cl–BF4, and ͑C͒ EMI–TFSI.
Scan rate was 50 mV/s.
Figure 4. Staircase cyclic voltammograms of 50 mM M Cu͑I͒ in EMI–DCA
recorded at ͑A͒ GC and ͑B͒ Ni electrodes at 313 K. Scan rate was 50 mV/s.
sults demonstrate that the type of the anions in the ILs can play an
important role in the chemical behavior of the metal species.
Diffusion coefficients of Cu͑I͒ and Cu͑II͒ species, respectively,
were estimated using data taken from chronoamperometry experi-
ments of 50 mM Cu͑I͒ and Cu͑II͒ solutions, respectively, on Pt and
GC electrodes. For the Cu͑I͒ species, the potential was stepped from
the open-circuit potential ͑OCP͒ of the Cu͑I͒ solution to 0.10 V,
1.1 V, which is less positive than that of the EMI–TFSI ͑1.8 V͒ but
more positive than that of the EMI–Cl–BF4 ͑0.5 V͒. This figure also
suggests that if there was any chloride impurities present in the
EMI–DCA, oxidation of chloride impurities would be observed near
0.5 V.
Up to 1.1 M of CuCl and 0.9 M of CuCl2 can be dissolved in the
EMI–DCA ionic liquid at room temperature. Similar to previous
studies reported for copper species in other ionic liquids,16,17 it was
found that, while the Cu͑I͒ solution is stable in the presence of
copper, Cu͑II͒ reacts with Cu to produce Cu͑I͒. Shown in Fig. 3A is
the cyclic voltammogram recorded on a polycrystalline Pt electrode
of a 50 mM Cu͑I͒ solution in an EMI–DCA ionic liquid prepared by
the direct dissolution of CuCl into the ionic liquid. For comparison,
Fig. 3B and C illustrates the cyclic voltammogram of a 50 mM
Cu͑I͒ solution in the chloride-rich EMI–Cl–BF4 and the EMI–TFSI
ionic liquid, respectively. Note that because the solubility of CuCl in
the EMI–TFSI ionic liquid is very limited, Cu͑I͒ solution has to be
generated by anodic dissolution. However, CuCl dissolves readily in
the EMI–Cl–BF4 ionic liquid. All three voltammograms exhibited
two redox couples. When the potential was initially scanned from
the rest potential toward the positive direction, Cu͑I͒ was oxidized
to Cu͑II͒ at wave a2 and the Cu͑II͒ was re-reduced back to Cu͑I͒ at
wave c2 when the potential scan was reversed. When the potential
was initially scanned from the rest potential toward the negative
direction, Cu͑I͒ was reduced to Cu metal at wave c1 and the depos-
ited Cu metal was reoxidized back to Cu͑I͒ at wave a1 when the
potential scan was reversed. As seen in these voltammograms, the
redox potentials of both the Cu͑II͒/Cu͑I͒ and Cu͑I͒/Cu͑0͒ couples in
the EMI–DCA and EMI–Cl–BF4 ionic liquids occurred at potentials
more negative than those observed in the EMI–TFSI ionic liquid,
consistent with the fact that the DCA− and Cl− anions are more basic
coordination ligands that complex with the Cu͑II͒ and Cu͑I͒ more
strongly than the TFSI− anion does. It can also be seen that the peak
potential separation between the cathodic peak and the anodic peak
for the Cu͑II͒/Cu͑I͒ couple in the EMI–DCA ionic liquid was much
less than that observed in the EMI–TFSI ionic liquid. Furthermore,
the peak current for the reductions of Cu͑II͒/Cu͑I͒ and Cu͑I͒/Cu͑0͒,
respectively, in the EMI–DCA IL was higher than that in the EMI–
TFSI and EMI–Cl–BF4 ILs. These results may be ascribed to the
more facile charge-transfer kinetics in the EMI–DCA IL, and the
lower viscosity of the EMI–DCA IL compared to that of the EMI–
TFSI and EMI–Cl–BF4 ILs. While the reduction potential of the
Cu͑I͒/Cu͑0͒ reaction in the EMI–DCA IL was slightly more negative
than that in the EMI–Cl–BF4 IL, the oxidation potential of the Cu͑I͒/
Cu͑II͒ reaction in the EMI–DCA IL was more positive than in the
EMI–Cl–BF4 IL. This may indicate that, while Cu͑I͒ is more stable
in EMI–DCA IL, Cu͑II͒ is more stable in EMI–Cl–BF4. These re-
Figure 5. Comparison of the dimensionless experimental curves derived
from current–time curves shown in the insets with the theoretical models for
3D nucleation/growth process. Insets: current–time transients of the chrono-
amperometric experiments recorded at GC and Ni electrodes for 50 mM
CuCl in EMI–DCA ionic liquid at 313 K.
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Journal of The Electrochemical Society, 155 ͑4͒ F55-F60 ͑2008͒
where the oxidation reaction was diffusion limited. For the Cu͑II͒
species, the potential was stepped from OCP to −0.28 V, corre-
sponding to the limiting currents for the reduction of Cu͑II͒. For
both species the current was found to follow the Cottrell behavior,
and the diffusion coefficients were calculated using the Cottrell
equation.23 Consistent with the lower viscosity of EMI–DCA IL, the
diffusion coefficient found for Cu͑I͒ and Cu͑II͒ in EMI–DCA were
2.13 ϫ 10−6 and 2.06 ϫ 10−6 cm2 s−1, respectively, which were
significantly larger than those reported in EMI–Cl–BF4 ͓2.3
ϫ 10−7 and 1.5 ϫ 10−7 cm2 s−1 for Cu͑I͒ and Cu͑II͒,
respectively͔.15
Cyclic voltammograms of copper species were also recorded at
nickel and glassy carbon electrodes as shown in Fig. 4. The same
redox couples observed in Fig. 3A were observed in these voltam-
mograms except that the Cu͑I͒/Cu͑II͒ redox couple could not be
observed at the Ni electrode because Ni was oxidized at a potential
less positive than the oxidation of Cu͑I͒. Unlike at the Pt electrode,
the deposition of copper at the Ni and GC substrates requires a
nucleation overpotential, as clearly indicated by the presence of the
“nucleation loop” in the voltammograms. To study the nucleation
process, chronoamperometry experiments were carried out in quies-
cent solutions containing 50 mM Cu͑I͒. These experiments were
carried out by stepping the potential of the working electrode from
where no reduction takes place to potentials sufficiently negative to
initiate the nucleation/growth process after a short induction time, to.
Typical current–time transients resulting from these experiments are
shown in the insets in Fig. 5. The transients exhibited the classic
shape for a nucleation process; after the capacitive current decay, the
current increased slowly until a current maximum, im, was reached
at time tm. The nucleation/growth process has been classified as
either “instantaneous” or “progressive.” The instantaneous model
refers to the situation in which all nucleation sites are activated at
the beginning of the potential step, whereas the progressive model
refers to the situation in which the nucleation sites gradually become
activated as the chronoamperometric experiment proceeds. To dis-
tinguish between the two nucleation/growth models, the data taken
from the chronoamperometric experiments were compared to the
2
theoretical dimensionless ͑i/im͒ vs ͑t/tm͒ curves developed by
Sharifker et al.24 for three-dimensional ͑3D͒ instantaneous and pro-
gressive nucleation, respectively. Before the fitting, the experimental
t and tm were corrected to t ͑=t − t ͒ and tЈ ͑=t − to͒. The experi-
Ј
o
m
m
mental and theoretical plots of ͑i/i ͒2 vs ͑t /tЈ ͒ are shown in Fig. 5.
Ј
m
m
It is apparent that the electrodeposition of Cu at both electrodes
involves a 3D-progressive nucleation/growth process. According to
Scharifker’s model, the product i2mt should be independent of the
applied deposition potential, and can be related to the concentration
and diffusion coefficient of Cu͑I͒ species as Eq. 4
i2mt = 0.2598͑nFC͒2D
͓4͔
where n is the number of charge transferred per Cu͑I͒, F is the
faradaic constant, C is the concentration of Cu͑I͒, and D is the
diffusion coefficient. The i2mt product obtained from the experimen-
tal i-t transients varied between 12 and 16 with an average of 14.2,
whereas the product estimated using the diffusion coefficient deter-
mined from the Cottrell equation was 12.9. The 3D-progressive
nucleation/growth process was also observed in a previous investi-
gation for the electrodeposition of copper on GC electrode in basic
chloroalumintate ionic liquids.14
Electrodeposition and characterization of copper.— Electrodepo-
sition of Cu was performed in EMI–DCA containing 50 mM Cu͑I͒
using bulk controlled-potential electrolysis experiments on nickel
wires ͑surface areas = 0.08 cm2͒. In the electrodepositing experi-
Figure 6. SEM micrographs of the copper electrodeposits that were prepared on nickel wires at 313 K by electrolysis of solutions of 50 mM CuCl in EMI-DCA
at −1.55, −1.65, −1.70, and −1.80 V. The charge passed during the electrolysis was 300 mC.
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Journal of The Electrochemical Society, 155 ͑4͒ F55-F60 ͑2008͒
F59
Figure 7. ͑A͒ SEM micrographs of the as-deposited copper that was prepared at 313 K by electrolysis of a solution of 50 mM CuCl in EMI–DCA at −1.65 V.
The charge for the electrolysis was 300 mC. ͑B͒ EDS profile of the sample shown in ͑A͒.
ments, a spiral wire of Cu was directly immersed in the electrolytic
solution as the counter electrode in order to compensate for the
consumption of the Cu͑I͒ species. After each electrolysis experiment
the Cu-deposited sample was rinsed thoroughly with deionized wa-
ter, dried, and examined by SEM, EDS, and X-ray diffraction
͑XRD͒. Figure 6 depicts SEM images of typical as-deposited Cu
samples. This figure shows that the electrodeposits produced at
lower overpotentials ͑−1.55 and −1.65 V͒, at which the deposition
rate is low, have a dense, fine-grained, and compact surface contain-
ing hemispherical nodules. As the deposition potential is made pro-
gressively more negative to −1.75 and −1.80 V, the deposits be-
come less compact and less uniform; cauliflower structures of
different sizes are observed. The formation of cauliflowers is appar-
ently due to the increased deposition rate. The micrograph of the
surface in higher magnification shown in Fig. 7A reveals that the
nodules are the cluster of Cu nanocrystals with average sizes of
about 40–100 nm. EDS analysis of the sample shown in Fig. 7B
indicates that it is free of the ionic liquid residual. The XRD patterns
of a typical Cu-deposited sample are shown in Fig. 8. This figure
clearly shows the characteristic diffraction patterns of crystalline Cu.
From the full-width at half-maximum ͑fwhm͒ of the Cu͑111͒ peak,
the averaged grain size of Cu was estimated using Scherrer’s
equation25 to be about 40 nm. This value agrees well with the SEM
micrograph shown in Fig. 7A.
Conclusion
The viscosity of the EMI–DCA IL is lower than the BF−4, PF6−,
and TFSI-based ILs and exhibits the Arrhenius temperature depen-
dence. CuCl and CuCl2 are very soluble in the EMI–DCA IL. The
reduction potentials observed for the Cu͑II͒/Cu͑I͒ and Cu͑I͒/Cu͑0͒
redox couples in the DCA-based ILs are different from those re-
ported in EMI–TFSI and EMI–Cl–BF4 ILs. Metallic copper coating
could be obtained on a Ni substrate by the potentiostatic reduction
of Cu͑I͒. The morphology of the as-deposited Cu coating depends
on the deposition potential. SEM and XRD results indicate that the
electrodeposits contained nanocrystalline Cu. The results observed
in this study reveal that DCA-based ILs would be useful electrolytes
for electrodeposition.
Acknowledgments
The authors gratefully acknowledge the financial support from
the National Science Council of Taiwan, grant no. NSC 96-2113-M-
006-015-MY3.
National Cheng-Kung University assisted in meeting the publication
costs of this article.
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