An investigation of silver electrodeposition from ionic liquids: Influence of atmospheric water uptake on the silver electrodeposition mechanism and film morphology

Article abstract of DOI:10.1016/j.electacta.2010.12.083

The electrodeposition of silver from two ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF₄]) and N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ([C ₄mPyr][TFSI]), and an aqueous KNO₃ solution on a glassy carbon electrode was undertaken. It was found by cyclic voltammetry that the electrodeposition of silver proceeds through nucleation-growth kinetics. Analysis of chronoamperometric data indicated that the nucleation-growth mechanism is instantaneous at all potentials in the case of [BMIm][BF ₄] and [C₄mPyr][TFSI], and instantaneous at low overpotentials tending to progressive at high overpotentials for KNO ₃. Significantly, under ambient conditions, the silver electrodeposition mechanism changes to progressive nucleation and growth in [C₄mPyr][TFSI], which is attributed to the uptake of atmospheric water in the IL. It was found that these differences in the growth mechanism impact significantly on the morphology of the resultant electrodeposit which is characterised ex situ by scanning electron microscopy and X-ray diffraction.

Full text of DOI:10.1016/j.electacta.2010.12.083

Electrochimica Acta 56 (2011) 2895–2905
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
An investigation of silver electrodeposition from ionic liquids: Influence of
atmospheric water uptake on the silver electrodeposition mechanism and film
morphology
Andrew Basilea,b, Anand I. Bhatt , Anthony P. O’Mullanea,∗∗,1, Suresh K. Bhargavaa
b,∗
a
School of Applied Sciences, RMIT University, G.P.O. Box 2476V, Melbourne, Victoria 3001, Australia
CSIRO Energy Technology, Clayton, Victoria 3169, Australia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The electrodeposition of silver from two ionic liquids, 1-butyl-3-methylimidazolium tetraflu-
oroborate ([BMIm][BF4]) and N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide
Received 9 December 2010
Accepted 29 December 2010
Available online 8 January 2011
([C4mPyr][TFSI]), and an aqueous KNO3 solution on a glassy carbon electrode was undertaken. It was
found by cyclic voltammetry that the electrodeposition of silver proceeds through nucleation–growth
kinetics. Analysis of chronoamperometric data indicated that the nucleation–growth mechanism is
instantaneous at all potentials in the case of [BMIm][BF4] and [C4mPyr][TFSI], and instantaneous at
low overpotentials tending to progressive at high overpotentials for KNO3. Significantly, under ambi-
ent conditions, the silver electrodeposition mechanism changes to progressive nucleation and growth
in [C4mPyr][TFSI], which is attributed to the uptake of atmospheric water in the IL. It was found that
these differences in the growth mechanism impact significantly on the morphology of the resultant
electrodeposit which is characterised ex situ by scanning electron microscopy and X-ray diffraction.
Keywords:
Ionic liquid
Silver electrodeposition
Nucleation–growth
©
2011 Elsevier Ltd. All rights reserved.
1
. Introduction
all of which have disadvantages including cost and slow deposi-
tion rates. Other approaches include electro and electroless plating,
however, this usually requires the use of toxic cyanide based plat-
ing baths that often contain additional organic additives, which are
both harmful and difficult to dispose of after the reaction completes.
Therefore, the development of alternative solvents that minimise
the use of pollutants is of importance given the industrial and
academic focus on green processes which aim to reduce the envi-
ronmental impact of current industrial methods.
The electrodeposition of silver from ionic liquids has been
suggested as an alternative to aqueous based electroplat-
ing baths. Initial electrodeposition studies focussed on the
use of chloroaluminate melts [7–10], however, the signifi-
cant air and moisture sensitivities of this class of ionic liquid
The electrodeposition of metals from ionic liquids (ILs) has
received significant interest. A recent review of this topic demon-
strated that a host of metals and alloys can be deposited in ionic
liquids due to their inherent properties such as chemical stability,
low/negligible vapour pressures, high ionic conductivity and wide
electrochemical window [1,2]. Compared to the currently used sol-
vents, the use of ionic liquids offers distinct advantages, such as
operating open plating baths at variable temperatures without the
release of harmful vapours and a lack of any hydrogen embrittle-
ment processes due to the hydrophobic nature of many ionic liquids
[
3,4].
There are many industrial applications that require homoge-
neous metal thin films. In particular, the electrodeposition of silver
is an important process given its use in microelectronics, jew-
ellery, aerospace and anti-bacterial applications [3,5,6]. Several
approaches have been taken to produce silver films including phys-
ical vapour deposition, chemical vapour deposition and sputtering,
would be a disadvantage for many industrial applications.
To alleviate these problems, environmentally stable ionic liq-
uids were employed for the electrodeposition of silver from
various salts at different substrates to generate either iso-
lated nanoparticles or continuous thin films, depending on the
electrodeposition parameters. The ILs studied have included 1-
butyl-3-methylimidazolium
tetrafluoroborate
1-butyl-3-methylimidazolium hexafluorophosphate
[BMIm][PF ]) [11,12], 1-ethyl-3-methylimidazolium tetraflu-
([BMIm][BF ])
4
[
3,11],
∗
Corresponding author.
Corresponding author. Tel.: +61 3 99259940; fax: +61 3 9925 3747.
E-mail addresses: anand.bhatt@csiro.au (A.I. Bhatt),
(
6
∗
∗
oroborate ([EMIm][BF ]) [13], 1-butyl-3-methylimidazolium
4
bis(trifluoromethanesulfonyl)imide ([BMIm][TFSI]) [14], N-butyl-
anthony.omullane@rmit.edu.au (A.P. O’Mullane).
1
N-methyl-pyrrolidinium
bis(trifluoromethanesulfonyl)imide
ISE member.
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.12.083

2
896
A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
(
[C mPyr][TFSI])
[15],
N-butyl-N-methyl-pyrrolidinium
accelerating voltage of 30 kV. Imaging of solids deposited on the
3 mm GC electrodes was performed with the aid of a custom built
electrode holder. Prior to SEM imaging, samples were thoroughly
rinsed with acetone and Milli-Q water and dried under a flow of
nitrogen. X-ray diffraction data were obtained with an AXS D8:
Discovery (Bruker) with General Area Detector Diffraction Sys-
tem (GADDS). Samples for transmission electron microscopy (TEM)
analysis were prepared by drop-casting the samples onto a carbon
coated copper grid and performed using a 1010 TEM instrument
(JEOL) operated at an accelerating voltage of 100 kV. UV/vis spec-
troscopy measurements of solutions were performed using a Cary
50 Bio-spectrophotometer (Varian). The moisture content for all ILs
used in this study were determined using Karl Fischer titration.
4
dicyanamide ([C mPyr][DCA]) [15], DIMCARB [16] and 1-butyl-
3
4
-methylimidazolium trifluoromethylsulfonate ([BMIm][OTf])
[
4]. However, to date few studies have systematically investi-
gated the influence of the properties of the ionic liquid on the
silver electrodeposition process [11]; instead, most studies have
concentrated on end applications.
In this work we report on the electrodeposition of silver from
commercially available ILs such as [BMIm][BF ] and N-butyl-
N-methyl-pyrrolidinium
(
and AgOTf, and also an aqueous KNO3 solution containing AgNO3
as a comparison. We have chosen the IL [C mPyr][TFSI] given its
lower reported viscosity than BF4 and PF6 based ILs, which
for the latter also have the disadvantage of decomposing to
produce hazardous species such as HF [17]. Given that industrial
applications cannot be carried out on a large scale under inert
atmosphere conditions without significantly increasing costs,
we have also investigated the influence of atmospheric water
4
bis(trifluoromethanesulfonyl)imide
[C mPyr][TFSI]) using readily available silver salts such as AgBF4
4
4
−
−
3. Results and discussion
3.1. Cyclic voltammetry studies
uptake in [C mPyr][TFSI] to probe the influence that it may have
A typical cyclic voltammogram for 20 mM AgBF in [BMIm][BF ]
4
4
4
on the silver electrodeposition process. Cyclic voltammetric and
chronoamperometric methods are used to elucidate the deposition
mechanism and the electrodeposits are characterised by scanning
electron microscopy (SEM) and X-ray diffraction (XRD) to probe
the significant solvent influence on the electrodeposition process.
(water content 1960 ppm) recorded at a GC electrode using a scan
−
1
rate of 50 mV s
is shown in Fig. 1a. The voltammogram was
scanned from 0.5 V to −0.9 V prior to switching of the scan direction.
The voltammetric peak profiles are consistent with that expected
for metal deposition and stripping from an electrode surface [19].
On the negative sweep the electrodeposition of Ag+ commences
at −0.220 V vs Ag QRE until the cathodic current reaches a maxi-
mum at −0.39 V, after which the current attains a diffusion limited
value until the end of the sweep at −0.90 V. On the reverse sweep
a current crossover is observed at −0.30 V which is indicative of
a nucleation–growth mechanism [4,11,20] after which a broad
oxidative stripping peak is observed at 0.16 V. This also indicates
that the electrodeposition of Ag on GC requires an overpotential
to initiate the nucleation and growth of bulk silver. Also shown in
Fig. 1b is the scan rate dependence on the electrodeposition pro-
cess, where a plot of peak current as a function of the square root
of scan rate exhibits a linear dependence over a scan rate range of
2
. Experimental
2.1. Materials
AgOTf (Sigma), AgBF4 (Aldrich), AgNO3 (Merck), ferrocene
(
Aldrich), [C mPyr][TFSI] (Merck), and [BMIm][BF ] (Io-Li-Tec)
4
4
were used as received. Aqueous solutions of 0.1 M KNO (Ajax) were
3
made up with deionized water (resistivity of 18.2 Mꢀ cm) purified
by use of a Milli-Q reagent deioniser (Millipore). Ionic liquids and
AgOTf were stored in a high purity Ar atmosphere glovebox (less
than 5 ppm H O) when not in use.
2
−
1
5
0–500 mV s , as expected for a diffusion controlled process. The
2
.2. Electrochemical measurements
small intercept that is observed is most likely due to changes in the
electrode area as silver is being deposited, as was observed previ-
ously for the electrodeposition of Ag on GC from DIMCARB [16]. As
◦
Voltammetric experiments were conducted at 20 ± 2 C with a
red
CH Instruments (CHI 760C) electrochemical analyser in an electro-
chemical cell that allowed reproducible positioning of the working,
reference, and auxiliary electrodes and a nitrogen inlet tube. A
shown in Table 1, the shift in Ep to more negative potentials on
increasing the scan rate is again indicative of a nucleation–growth
ox
process [21] whereas the electrodissolution potential, Ep , of silver
2
0
.0707 cm glassy carbon (GC) electrode (BAS) was used as the
from the GC surface shows significantly less dependence on sweep
rate; only a shift of 26 mV is observed over the scan rate range of
working electrode. Prior to electrodeposition the electrode was
polished with an aqueous 0.3 ␮m alumina slurry on a polishing
cloth (Microcloth, Buehler), thoroughly rinsed with Milli-Q water,
and dried with a flow of nitrogen gas. The reference electrode was
−
1
50–500 mV s
.
Fig. 1c shows a typical voltammogram recorded at a GC electrode
−
1
for a solution of 10 mM AgOTf in dry [C4mPyr][TFSI] at 50 mV s
Ag/AgCl (aqueous 3 M KCl) for experiments carried out in aque-
(60 ppm water content). On the negative sweep, electrodeposition
+
+
ous solution and an Ag/Ag (10 mM AgOTf in [C mPyr][TFSI]) for
commences at −0.15 V vs Ag/Ag reference electrode and reaches
4
experiments carried out in [C mPyr][TFSI] [18]. In the case of exper-
a maximum at −0.20 V, after which a diffusion limited current is
attained until the end of the sweep. On the reverse sweep a cur-
rent crossover is observed at −0.16 V indicative of a nucleation and
growth process which is followed by an oxidative stripping peak
4
iments carried out in [BMIm][BF ] a quasi silver reference electrode
4
was employed in order to minimise junction potentials arising
+
from use of the Ag/Ag (10 mM AgOTf in [C mPyr][TFSI]). For elec-
4
red
trodeposition experiments a GC electrode was used as the working
electrode and a platinum wire (BAS) as the counter electrode. All
electrochemical experiments were commenced after degassing the
electrolyte solutions with nitrogen for at least 10 min prior to any
measurement.
at 0.14 V. The observed shift in Ep to more negative potentials on
increasing the scan rate is again suggestive of a nucleation–growth
process (Table 1). The plot of peak current as a function of the square
root of scan rate (Fig. 1d) exhibits a linear dependence over a scan
−
1
rate range of 50–500 mV s . As observed in the previous case an
intercept is present in the plot of peak current vs square root of scan
rate. This intercept is markedly larger than that observed in the case
2.3. Physical characterisation
of [BMIm][BF ] and the excess current is attributed to a combina-
4
Scanning electron microscopy (SEM) measurements were per-
formed on an FEI Nova SEM (Philips) instrument with an AMETEK
energy dispersive X-ray (EDX) system (Nova 200) operated at an
tion of growth in electrode area due to silver electrodeposition and
chemical reaction occurring between the silver cation and ionic liq-
uid. This type of behaviour has previously been observed in the case

A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
2897
Fig. 1. Cyclic voltammograms for reduction of Ag+ to Ag onto GC electrodes at a scan rate range of 50 to 500 mV s ; (a) 20 mM AgBF4 in [BMIm][BF4] and (b) plot of deposition
−1
current as function of square root of scan rate; (c) 10 mM AgOTf in dry [C4mPyr][TFSI] and (d) plot of deposition current as function of square root of scan rate; and (e) 5 mM
◦
AgNO3 in 0.1 M KNO3 and (f) plot of deposition current as function of square root of scan rate. All CVs measured at 20 C under inert atmosphere.
of a distillable ionic liquid, DIMCARB [16] and is detailed further in
the following section.
Typical voltammograms obtained for the deposition of silver
from 10 mM AgNO3 in 0.1 M KNO3 are shown in Fig. 1e. The onset
potential for electrodeposition of silver is 0.36 V vs Ag/AgCl with
a current maximum at 0.16 V, after which a steady state current
is observed until the end of the sweep at −0.60 V. On the positive
sweep a current crossover is observed at 0.30 V and the reduction
Table 1
Cyclic voltammetric data obtained for reduction of Ag+ to Ag onto GC electrodes from 20 mM AgBF4 in [BMIm][BF4], 10 mM AgOTf in dry [C4mPyr][TFSI], 10 mM AgOTf in
◦
a
wet [C4mPyr][TFSI] and 5 mM AgNO3 in 0.1 M KNO3 at 20 C under inert atmosphere. Voltammetric data obtained as a function of sweep rate.
Scan rate (mV s 1
−
)
E
red
p
(V)
E
ox
p
(V)
Em (V)
ꢁE po x-red (V)
Qred (mC)
Qox (mC)
Qox/Qred
Electrodeposition of silver onto a GC electrode from a solution containing 20 mM AgBF4 in [BMIm][BF4]
5
0
−0.386
−0.395
−0.430
−0.445
−0.479
−0.501
0.161
0.164
0.162
0.184
0.186
0.187
−0.113
−0.116
−0.134
−0.131
−0.147
−0.157
0.547
0.559
0.592
0.629
0.665
0.688
0.24
0.20
0.16
0.12
0.10
0.10
0.22
0.19
0.15
0.12
0.10
0.09
0.92
0.95
0.94
1.00
1.00
0.90
100
200
300
400
500
Electrodeposition of silver onto a GC electrode from a solution containing 10 mM AgOTF in dry [C4mPyr][TFSI] (water content of 60 ppm)
5
0
−0.201
−0.228
−0.261
−0.290
−0.306
−0.323
0.216
0.208
0.197
0.179
0.160
0.144
0.008
−0.010
−0.032
−0.056
−0.073
−0.090
0.417
0.436
0.458
0.469
0.466
0.467
0.16
0.10
0.07
0.06
0.05
0.05
0.15
0.10
0.07
0.06
0.05
0.04
0.94
1.00
1.00
1.00
1.00
0.80
100
200
300
400
500
Electrodeposition of silver onto a GC electrode from a solution containing 10 mM AgOTF in wet [C4mPyr][TFSI] (water content of 460 ppm)
−
−
−
3
3
3
3
3
3
−3
−3
−3
−3
−3
−3
5
0
−0.673
−0.756
−0.851
−0.881
−0.930
−0.968
−0.109
−0.113
−0.178
−0.176
−0.162
−0.117
−0.283
−0.322
−0.337
−0.353
−0.384
−0.423
0.783
0.869
1.029
1.057
1.092
1.085
5.09 × 10
6.86 × 10
8.93 × 10
4.10 × 10
5.57 × 10
8.10 × 10
9.91 × 10
0.81
0.81
0.91
0.87
0.86
0.86
1
2
3
4
5
00
00
00
00
00
−
−
−
11.3 × 10
12.6 × 10
14.3 × 10
10.9 × 10
12.2 × 10
Electrodeposition of silver onto a GC electrode from a solution containing 5 mM AgNO3 in 0.1 M KNO3
5
0
0.164
0.109
0.082
0.023
0.004
0.016
0.563
0.569
0.592
0.594
0.615
0.364
0.339
0.337
0.309
0.310
0.316
0.399
0.460
0.510
0.571
0.611
0.599
1.00
0.64
0.42
0.35
0.30
0.27
0.88
0.56
0.39
0.29
0.26
0.24
0.88
0.88
0.93
0.83
0.87
0.89
1
2
3
4
5
00
00
00
00
00
0.615
ꢀ
ꢁ
a
red
E
+ Ep /2 in volts vs the relevant reference electrode. E pr ed and E po x are reduction and oxidation peak potentials,
ox
Em represents the midpoint potential measured as
p
respectively; Qred and Qox are the charges associated with the reduction and oxidation processes.

2
898
A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
peak potential shifts to less positive potentials on increasing the
scan rate, indicating again a nucleation–growth process. The broad
oxidative stripping peak at 0.56 V remains largely unaffected by
increasing sweep rate. The reduction peak current is proportional
to the square root of scan rate (Fig. 1f) indicating a diffusion con-
trolled process, again with the observation of a non zero intercept
due to concomitant changes in electrode area from deposition of a
conductive metal.
tion of surface oxides. Similar to the aqueous system, CVs of silver
electrodes in [C mPyr][TFSI] show presence of surface oxides in the
4
wet IL (Fig. 2d). Interestingly in the case of the dry IL (Fig. 2d) this
0
behaviour is not replicated and only anodic dissolution of Ag to
+
Ag is observed. This implies that silver oxide formation in the IL
system only occurs if sufficient water is present.
The observation that silver nanoparticles are chemically formed
from AgOTf in [C mPyr][TFSI] was also experimentally observed by
4
In the case of the aqueous solution, the ratio of the charge asso-
UV/vis spectroscopy (Fig. 4a), which clearly shows a surface plas-
mon resonance feature at 483 nm indicative of silver nanoparticle
formation [23,24]. The presence of Ag nanoparticles was also con-
firmed by TEM imaging (Fig. 4b), EDX analysis during SEM imaging
and XRD measurements which showed reflections due to fcc silver.
This phenomenon was observed after exposure of the electrolyte
solution to atmosphere after ca. 1 h but was only observed under
inert conditions after a time period of greater than 5 h. This is most
likely related to the water content of the IL, which was found to be
60 ppm under glovebox conditions and 460 ppm under benchtop
conditions using Karl Fischer measurements. These values are in
close agreement with those obtained by Compton for the same IL
[25]. It should be noted that silver solutions prepared and stored
in the dark also formed nanoparticles in a similar timeframe which
discounts the possibility that nanoparticle formation is occurring
from reaction with UV radiation from sunlight. This finding sug-
gests that the nanoparticle formation mechanism is related to the
reaction of Ag+ with electrolyte moieties rather than the effects
of direct UV irradiation. The nature of the chemical interaction
between silver ions and the IL moieties is not clear at present. It has
been shown previously that monovalent Cu and Ag+ ions can dis-
proportionate to form the M2+ ion and M0 in the presence of water
and chelating ligands such as 5,5,7,12,12,14-hexamethyl-1,4,8,11-
tetraazacyclotetradecane (ligand L) [26]. Since Ag+ is known to be
chelated/coordinated by the TFSI anion [27] we hypothesise that
a similar reaction mechanism may be occurring as shown by the
following reaction:
ciated with the stripping process to the reduction process, Qox/Qred
,
is always less than one (Table 1), which indicates that the removal
of silver from a GC surface is not a fully chemically reversible pro-
cess. However, in the case of both ionic liquids nearly full chemical
reversibility is seen for silver deposition/stripping (Table 1). The
oxidative removal of silver in the aqueous solution at pH = 5.4 may
be complicated due to the formation of some surface oxides on
silver during the oxidation sweep and may account for the lack
of full chemical reversibility. This is observed in Fig. 2 where CVs
are obtained using a silver electrode at different pH values. In 1 M
H SO , pH = 0.45 (Fig. 2a), the anodic current clearly increases with-
2
4
out the appearance of any peak maximum due to dissolution of Ag
+
to Ag . When this experiment is performed in 1 M NaOH, pH = 13
(
Fig. 2b) it can be seen clearly that there are peaks associated with
the formation of oxides on the silver surface [22]. Under the con-
ditions of our electrodeposition experiments which were carried
out in 0.1 M KNO , pH = 5.4 (Fig. 2c) it can be seen that there is a
3
distinct anodic peak prior to the onset of bulk dissolution of Ag into
+
Ag which indicates some oxide formation. This may be the origin
+
of the lack of chemical reversibility seen in the aqueous case for
silver deposition/stripping.
3
[
.1.1. Influence of water content on silver electrodeposition in
C4mPyr][TFSI]
In all cases the electrodeposition of silver is sensitive to the
nature of the electrode surface, which can be alleviated through rig-
orous polishing procedures. However, in the case of [C mPyr][TFSI]
4
H
O
+
2
2+
0
it was found that performing the silver electrodeposition exper-
iments on the bench rather than under dry glovebox conditions
resulted in significantly different electrochemical behaviour. After
2
Ag + nTFSI−→ Ag(TFSI) + Ag
(1)
n
UV/vis spectra of [C mPyr][TFSI] after reaction to form the
4
exposure of the AgOTf in [C mPyr][TFSI] electrolyte to ambient con-
nanoparticles and subsequent removal of the nanoparticles by cen-
trifugation show a broad band centred at ca. 350 nm (Fig. 4a).
Previously, it has been shown that the d–d transition for Ag2+ is
in the region of 348–376 nm [28]. The spectral data obtained tenta-
tively supports the disproportionation theory for formation of Ag0
by Reaction (1).
4
ditions, it was noticed during CV experiments that sometimes a
shoulder appeared with the main deposition process during the
reduction sweep (data not shown). If CVs are recorded after full
atmospheric water absorption occurs (460 ppm H O content) in the
2
‘
wet’ [C mPyr][TFSI], significant differences in the voltammetry can
4
+
0
The voltammetric response of the Ag2+/Ag+ couple has been
previously explored and is found to be at more negative poten-
be observed (Fig. 3). Firstly, the reduction process due to Ag → Ag
reaction is shifted ca. 400 mV to more negative potentials. Secondly,
a significant decrease in current density is observed. Thirdly, two
shoulders are observed in addition to the main reduction process.
These are attributed to the reduction of Ag2 and deposition of Ag
onto adsorbed silver nanoparticles on the GC surface (see below
for discussion). Similar behaviour has been observed previously for
Ag electrodeposition from DIMCARB on GC, where two reduction
processes were observed and attributed to the reduction of silver
on GC and silver on silver nanoparticles adsorbed on the electrode
and formed chemically from the slow reaction of DIMCARB with sil-
ver ions [16]. Additionally, in that study a shifting of the reduction
potential by up to 1 V was observed due to the effect of nanopar-
+
0
tials compared to the Ag /Ag process. Based on these results the
small shoulder observed in Fig. 3 at −0.930 V may be attributed to
+
2+
Ag reduction, further supporting the disproportionation theory.
The 255 mV peak–peak separation is close to that of ca. 250 mV
reported by Sroczynski and Grzejdziak for Ag2+ isocyclam com-
plexes in aqueous solution [28]. Based on this analysis the final
+
process at −1.190 V is then attributed to the reduction of Ag to
0
Ag onto silver nanoparticles which are adsorbed onto the GC sur-
+
face as also observed previously in the case of Ag reduction from
DIMCARB [16].
It has been shown that the disproportionation reaction in wet
organic solvents in the presence of the chelating ligand, L, produces
a mirror on the walls of the reaction vessel [26], that is bulk for-
mation of silver metal occurs. It has also been shown that in dry
solvents, i.e., in the absence of water, this reaction does not occur
[26]. Since the ILs used in the study have low to moderate levels of
water impurity, combined with a chelating ligand (TFSI anion) the
disproportionation reaction can occur. Presumably, the higher vis-
cosity of the IL and/or lower equilibrium constants results in slower
ticle adsorption onto the GC surface. If the silver/[C mPyr][TFSI]
4
electrolyte solution is left for sufficient time then only a single
deposition process is observed, however, the deposition potential
is significantly shifted to further negative potentials. It can also be
seen that the Qox/Qred ratio is less than one (Table 1) and is similar
to the case of silver deposition and stripping from aqueous solu-
tion and suggests that the presence of atmospheric water impacts
on the chemical reversibility of the system by the possible forma-

A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
2899
◦
Fig. 2. Cyclic voltammograms obtained for a silver electrode in 1 M H2SO4 (pH = 0.45), 1 M NaOH (pH = 13) and 0.1 M KNO3 (pH = 5.4) measured at 20 C and a scan rate of
−1
0
.05 V s
.
formation of the silver metal and thus enables nanoparticles to be
In light of the fact that silver nanoparticles are formed under
ambient conditions (with associated voltammetric changes), and
given that the reference electrode employed was an Ag/Ag (10 mM
+
formed as opposed to bulk metallic silver. If the [C mPyr][TFSI]/Ag
4
+
solution is left in a sealed vessel for a long time period (4 weeks)
the eventual formation of a silver deposit on the walls of the vessel
does occur due to the eventual diffusion and combination of the
reactive nanoparticles to form the bulk metal.
silver triflate in [C mPyr][TFSI]) [18] the stability of the reference
4
electrode was also tested under glovebox conditions and on the
bench using ferrocene as a redox probe. It was found that there was
◦
−1
Fig. 3. (a) Cyclic voltammogram of 10 mM AgOTf in wet [C4mPyr][TFSI] measured at 20 C under inert atmosphere using a scan rate of 0.05 V s and (b) plot of deposition
current as a function of square root of scan rate.

2
900
A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
Fig. 4. (a) UV/vis spectra of 10 mM AgOTf in [C4mPyr][TFSI] (—) recorded 24 h after dissolution, also shown neat [C4mPyr][TFSI] (· · ·) and [C4mPyr][TFSI] after removal of
+
nanoparticles by centrifugation; (b) TEM images of silver nanoparticles formed by chemical reduction of Ag in [C4mPyr][TFSI].
0
no difference in the E value recorded for the ferrocene/ferricinium
process under these different conditions. This therefore suggests
that the shifts in the onset for silver electrodeposition are related
to the nature of the electrode surface. Previously Snook et al. have
commented upon the stability of this reference electrode under
inert conditions [18], and it would appear that the reference also
shows stability under ambient conditions.
where J is the current density at time t and Jm is the maximum
current density at time tm.
In the case of instantaneous nucleation adatoms are deposited
onto the electrode surface and grow at a constant rate that is
dependent on the applied potential. The resultant J–t curves are
mathematically described by the following equation.
For 3D instantaneous nucleation and 2D growth:
ꢂ
ꢃ
2
ꢈ
ꢉ
ꢂ
ꢃꢊꢋ
2
J
1.9542
t/tm
t
=
1 − exp −1.2564
(3)
3
.2. Chronoamperometry
Jm
tm
Additional information regarding the silver diffusion coefficient
Chronoamperometry was employed to probe the nucleation
and number of nuclei on the electrode surface can also be extrap-
olated from the CA data using the Hills–Scharifker methodology,
which is described by the following Eqs. (4)–(9). Data calculated
using Eqs. (4)–(9) are shown in Table 2 for all of the systems used
in this study.
and growth mechanism suggested by the voltammetric data.
Chronoamperograms were recorded at a GC electrode and the
potential was stepped from an initial value where no deposition
occurs to successively negative potential values close to Ep and
beyond. Typical chronoamperograms obtained are shown in Fig. 5.
In all cases the J–t curves for potential values close to Ep show an
initial current maximum Jm at time tm, which then quickly decays
to a diffusion limited current. At potentials sufficiently negative
from Ep the current response is described by the well-known t
red
In the case of progressive nucleation:
red
ꢂ
ꢃ
1/2
4.6733
tm =
(4)
AN ꢂkꢀD
∞
red
−1/2
Jm = 0.4615 nFD /4Cbulk(k AN∞)
3
ꢀ
1/4
(5)
(6)
Cottrellian decay and no current maximum is observed.
A number of models have been developed to describe the J–t
curves for metal electrodeposition. It has been shown previously
that the theoretical methodology developed by Scharifker and Hills
2
2
I tm = 0.2598(nFC
) D
m
bulk
1.2564
tm =
(7)
[
29] is applicable to deposition from IL media [16,30,31]. It has been
NꢂkD
previously reported by Milchev et al. during metal electrodeposi-
tion in the absence of supporting electrolyte, when ion migration
effects become prominent, that substantially different J–t curves
are observed [32]. However, in the case of ionic liquids the concen-
tration of ions is higher than that in aqueous systems which negates
the possibility of any ion migration effects. Indeed the J–t curves are
typical for that found for a 3D nucleation and growth process with-
out interference from ohmic, diffusion or ion transfer limitations.
Therefore, in this study the Hills–Scharifker treatment was applied
which describes two limiting cases, progressive and instantaneous
growth mechanisms, for the initial stages of 3D nucleation and 2D
growth of deposited nuclei. In the case of progressive nucleation
where the initially deposited adatoms grow at varying rates depen-
dent on time of deposition, the J–t curves can be mathematically
described by the following equation.
Jm = 0.6382 nFDCbulk(kN)1/2
(8)
(9)
2
2
J tm = 0.1629(nFC
) D
m
bulk
where N is the number of nuclei, D is the diffusion coefficient, C
bulk
is the bulk concentration, k = (8ꢂCbulkM/ꢃ)1 (M is the molar mass
/2
of the depositing species and ꢃ is the density of depositing species)
ꢀ
1/2
and k = (4/3)(8ꢂCbulkM/ꢃ)
.
T
y
p
i
c
a
l
J
–
t
c
u
r
v
e
s
o
b
t
a
i
n
e
d
f
o
r
A
g
B
F
r
e
d
u
c
t
i
o
n
i
n
[
B
M
I
m
]
[
B
F
]
4
4
(presented as non-dimensional plots) are shown in Fig. 5a with the
theoretical curves predicted by Eqs. (2) and (3). These results are
typical of this analysis of the experimental responses observed in
this study as can be seen for the case of [C mPyr][TFSI] where the
original experimental J–t curves are illustrated (in Fig. 5e). As can
be observed, the best fit of the data suggests that Ag is reduced and
deposited onto the GC electrode surface via an instantaneous mech-
anism. The results presented in this study show good correlation
with the theoretical curves. This is in contrast to similar experi-
ments performed by He et al. [11] where the chronoamperometry
data showed intermediate behaviour attributed to nuclei growth
4
+
For 3D progressive nucleation and 2D growth:
ꢄ
ꢅ
ꢆꢇ
ꢂ
ꢃ
2
ꢂ
ꢃ
2
2
J
1.2254
t/tm
t
=
1 − exp −2.3367
(2)
Jm
tm

A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
2901
Table 2
Chronoamperometric data obtained for reduction of Ag+ to Ag onto GC electrodes from 20 mM AgBF4 in [BMIm][BF4], 10 mM AgOTf in dry [C4mPyr][TFSI], 10 mM AgOTf in
◦
wet [C4mPyr][TFSI] and 5 mM AgNO3 in 0.1 M KNO3 at 20 C under inert atmosphere.
Jm (A cm−2)
J
2
tm (A2 cm s)
−4
D (cm2
s )
−1
Estep (V)
tm (s)
m
2
−
−
−
0 mM AgBF4 in [BMIm][BF4]
−
−
−
4
4
4
−8
−8
−8
−8
−8
−8
0.25
0.30
0.35
1.4
0.4
0.4
2.1 × 10
2.2 × 10
2.9 × 10
6.5 × 10
1.9 × 10
3.4 × 10
1.1 × 10
3.1 × 10
5.6 × 10
−
8
Calculated D: 6.5 ± 2.8 × 10
1
−
−
−
−
−
0 mM AgOTf in dry [C4mPyr][TFSI]
−
−
−
−
−
4
4
4
4
4
−9
−8
−8
−8
−8
−8
−8
0.25
0.30
0.35
0.40
0.45
0.5
1.3
0.3
0.3
0.1
1.1 × 10
1.3 × 10
2.7 × 10
2.7 × 10
3.8 × 10
5.7 × 10
2.2 × 10
2.3 × 10
2.2 × 10
1.5 × 10
2.4 × 10
9.0 × 10
−8
9.3 × 10
−8
9.2 × 10
−8
6.1 × 10
−
8
Calculated D: 2.6 ± 1.7 × 10
1
−
−
−
−
−
−
−
−
−
−
−
−
−
−
0 mM AgOTf in wet [C4mPyr][TFSI]
−
−
−
−
−
−
−
−
−
−
−
−
−
−
4
4
4
4
4
4
4
4
4
4
4
4
4
4
−8
−9
−10
−8
−8
−8
−8
−8
−9
−9
−8
−8
−8
−9
−8
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.1
0.5
0.03
0.3
0.2
0.1
0.1
0.1
0.06
0.08
0.09
0.06
0.04
0.04
1.2 × 10
1.4 × 10
1.8 × 10
1.9 × 10
2.8 × 10
3.4 × 10
2.9 × 10
2.9 × 10
3.5 × 10
3.1 × 10
3.4 × 10
4.3 × 10
5.2 × 10
4.2 × 10
1.6 × 10
9.3 × 10
9.0 × 10
1.0 × 10
1.2 × 10
1.3 × 10
1.1 × 10
1.1 × 10
8.0 × 10
8.4 × 10
1.1 × 10
1.2 × 10
1.1 × 10
7.7 × 10
6.8 × 10
−8
3.8 × 10
−9
3.7 × 10
−8
4.2 × 10
−8
5.0 × 10
−8
5.2 × 10
−8
4.7 × 10
−8
4.4 × 10
−8
5.3 × 10
−8
5.6 × 10
−8
4.5 × 10
−8
5.0 × 10
−8
4.5 × 10
−8
3.2 × 10
−
8
Calculated D: 4.5 ± 0.9 × 10
5
mM AgNO3 in 0.1 M KNO3
−
−
−
−
−
−
−
−
−
−
−
−
−
−
4
3
3
3
3
3
3
3
3
3
3
3
2
2
−7
−7
−7
−7
−7
−7
−7
−7
−6
−6
−7
−7
−7
−6
−6
0
0
0
0
0
0
0
0
−
−
−
−
−
−
.35
.30
.25
.20
.15
.10
.05
.00
0.05
0.10
0.15
0.20
0.25
0.30
0.5
7.8 × 10
2.2 × 10
6.7 × 10
2.3 × 10
2.8 × 10
3.3 × 10
3.9 × 10
3.9 × 10
4.2 × 10
5.5 × 10
6.9 × 10
9.4 × 10
1.1 × 10
1.3 × 10
3.3 × 10
1.2 × 10
2.6 × 10
5.0 × 10
4.9 × 10
6.2 × 10
6.6 × 10
9.5 × 10
1.0 × 10
1.0 × 10
9.6 × 10
8.8 × 10
9.5 × 10
1.0 × 10
8.6 × 10
−6
0.02
0.006
0.1
3.1 × 10
−6
6.9 × 10
−5
1.3 × 10
−5
0.06
0.05
0.04
0.06
0.05
0.03
0.02
0.01
0.008
0.006
1.3 × 10
−5
1.6 × 10
−5
1.7 × 10
−5
2.5 × 10
−5
2.7 × 10
−5
2.7 × 10
−5
2.5 × 10
−5
2.3 × 10
−5
2.5 × 10
−5
2.7 × 10
−
5
Calculated D: 1.8 ± 0.7 × 10
controlled by both mixed kinetics and diffusion [11,33]. We note
the best fit of the data suggests an instantaneous mechanism. How-
ever, significant differences in behaviour are observed if the dry IL
is allowed to absorb moisture from the atmosphere. Plots of the
J–t curves in this case are shown in Fig. 5c and the data is best
described by the theoretical transients for progressive nucleation
and growth. Clearly, the effect of water impurity on this deposition
reaction is significant enough to change the initial silver deposition
mechanism. These mechanistic changes are also highlighted in the
deposit morphologies as shown in the SEM images (see Section 3.3).
Since care was taken to ensure that the contribution from chem-
ically formed nanoparticles was minimal and that the deposition
conditions were the same (including shielding from UV radiation),
this mechanistic change is most likely the sole result of an increase
in water content which may affect the interfacial double layer of
the working electrode, kinetics of the electrodeposition process and
viscosity of the ionic liquid.
+
that He et al. used dried [BMIm][BF ] and a higher Ag concentra-
4
tion [11] whereas the IL used in this study was not further purified
from supplier specifications. Clearly, the combined effects of water
impurity from atmospheric absorption and lowering the Ag+ con-
centration serves to reduce the mixed kinetic effects noted by He
et al. [11], resulting in instantaneous behaviour. The instantaneous
nature of deposition has also been confirmed by SEM analysis (see
Section 3.3).
Due to the Ag nanoparticle formation reaction in [C mPyr][TFSI],
4
the chronoamperometric data was measured as a function of either
dried or wet (from absorption of atmospheric water) IL. In both
cases the data was recorded immediately after dissolution of the
silver salt in the IL. This minimised the effects on the electro-
chemistry results from contributions due to the coupled chemical
reaction that causes nanoparticle formation. It has previously been
shown that electrochemical measurements can be made when sil-
ver nanoparticle chemical formation occurs if the data collection
time is short compared to the nanoparticle formation time [16].
However, some care should be taken when interpreting results as
contributions from a coupled chemical process cannot be entirely
discounted.
Turning to the deposition of Ag from 0.10 M KNO /water, the J–t
3
curves are shown in Fig. 5d. The data obtained is strongly depen-
dent on the deposition voltage. At potentials close to the onset
potential for Ag deposition of 0.35 V the J–t curves are best fit-
ted by the theoretical transients for instantaneous nucleation and
growth. However, as the potential is successively stepped towards
red
In the case of dry [C mPyr][TFSI] the non-dimensional J–t curves
E
(−0.15 V), the nature of the mechanism changes and tends
4
p
are shown in Fig. 5b. As was also found for the case of [BMIm][BF ],
towards progressive nucleation and growth. This phenomenon was
4

2
902
A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
Fig. 5. Nondimensional plots of (j/jm)2 vs t/tm for the electrodeposition of silver from (a) 20 mM AgBF4 in [BMIm][BF4]; (b) 10 mM AgOTf in dry [C4mPyr][TFSI]; (c) 10 mM
AgOTf in wet [C4mPyr][TFSI]; (d) 5 mM AgNO3 in 0.1 M KNO3. Overlayed are the theoretical curves calculated using Eqs. (2) and (3) for instantaneous (—) and progressive (· · ·)
nucleation and diffusion limited growth and (e) typical plots obtained of current vs time for 10 mM AgOTf in dry [C4mPyr][TFSI]: shown data obtained at stepping potentials
of 0.5–1.0 V in 0.1 V steps.
not observed in the case of Ag electrodeposition from [BMIm][BF4]
diffusion fields of the nuclei do not overlap. Thus, if care is taken
to analyse data from the very early portion of the current tran-
sient. Eq. (10) can be used to estimate the value of N0 for all the
systems studied. Using this methodology we have estimated the
number of nuclei formed during the very early stages of nucleation
to allow trends to be ascertained between the different solvent
systems studied.
and dry [C mPyr][TFSI].
4
It has been shown previously that the number density of nuclei
formed has a dependence on the overpotential applied. Gunawar-
dena et al. have shown that the nucleation number density, N , can
0
be calculated from the rising portion of the J–t curves using the
following relationship [34]:
A plot of N0 calculated using Eq. (10) as a function of depositing
voltage is shown in Fig. 6. In the case of the aqueous system the data
shows that at overpotentials which lead to an eventual instanta-
)3/2M1/2N t
ꢃ1/2
1/2
J = 1.04 nFꢂ(2DCbulk
(10)
0
red
neous nucleation mechanism, at voltages close to E , the initially
During the initial stages of deposition, well before the maxima
in the J–t curves, the initial nucleation can be considered to be effec-
tively instantaneous [34]. This theory, proposed by Gunawardena
et al. [34], analyses the deposited nuclei at an early stage when the
p
red
high values of N decay to lower values as E is approached. How-
0
p
ever, as the deposition overpotential voltage is increased into the
region where an eventual progressive nucleation mechanism oper-

A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
2903
Fig. 6. Plot of nucleation number density (N0) calculated using Eq. (10) as a function of applied potential for Ag deposition onto GC from 5 mM AgNO3 in 0.1 M KNO3 (left)
and ionic liquids (right): 20 mM AgBF4 in [BMIm][BF4] (ꢀ), 10 mM AgOTf in dry [C4mPyr][TFSI] (×) and 10 mM AgOTf in wet [C4mPyr][TFSI] (ꢄ).
ates, the values of N begin to rise in a linear relationship. Given that
nucleation mechanism was predicted to operate after analysis of
0
Eq. (10) refers to the case of instantaneous nucleation at very short
times it is interesting to correlate the number of nuclei formed at
this short time scale. However, the number of nuclei calculated is
only used to observe trends between the different solvent systems
and is not taken as the absolute number of nuclei formed.
the full transient. The data for [C mPyr][TFSI] would then appear
4
to show a similar trend to the aqueous case if the effect of the
water impurity is discounted. It is tentatively proposed that the
effect of water addition to the IL is as follows. As water con-
tent is increased significantly, the physical properties of the IL
change and a concomitant decrease in viscosity and hence increase
in mass transport is obtained. This is reflected by the increase
In the case of the ILs, the data for [C mPyr][TFSI] show that
4
high values of N0 are observed for the dry IL, similar to the aque-
ous case. However, in the case of the wet IL, lower values of N0
are observed that follow a linear relationship when a progressive
+
−8
in dry
in the diffusion coefficient of Ag from 2.6 ± 1.7 × 10
−
8
2
−1
[C mPyr][TFSI] to 4.5 ± 0.9 × 10 cm s in [C mPyr][TFSI] after
4
4
Fig. 7. SEM images of Ag deposits on GC electrode from (a) deposition at −0.15 V vs Ag/AgCl/KCl from 5 mM AgNO3 in 0.1 M KNO3; (b) deposition at 0.20 V vs Ag/AgCl/KCl from
mM AgNO3 in 0.1 M KNO3; (c) deposition at −0.80 V vs Ag QRE from 20 mM AgBF4 in [BMIm][BF4]; (d) higher magnification of sample from (c); (e) deposition at −0.75 V vs
Ag/AgOTf/[C4mPyr][TFSI] from 10 mM AgOTf in dry [C4mPyr][TFSI]; (f) higher magnification of sample from (e); (g) deposition at −0.80 V vs Ag/AgOTf/[C4mPyr][TFSI] from
0 mM AgOTf in wet [C4mPyr][TFSI]; (h) higher magnification of sample from (g).
5
1

2
904
A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
Fig. 8. X-ray diffraction patterns for Ag deposits on GC electrodes from [BMIm]BF4], wet and dry [C4mPyr][TFSI] and AgNO3 in 0.1 M KNO3. Data collected using a General
Area Detector Diffraction System (GADDS).
atmospheric uptake of water. Thus the increase in available Ag+
ions at the electrode surface, in combination with the required
high overpotentials for deposition due to the change in IL prop-
erties, results in greater numbers of Ag nuclei forming on the GC
electrode. The obvious assumption here is that the water impu-
from the 0.10 M KNO /water system obtained from a deposi-
3
−
2
tion potential of −0.15 V and 90 mC cm . The morphology of the
deposited silver shows significant dendritic growth and a fern
like structure. This deposition morphology implies that the CA
data, which suggested at a potential of −0.15 V the Ag nucleation
and growth mechanism is progressive in nature during the ini-
tial stages of deposition. However, if the deposition potential is
changed to +0.20 V, as shown in Fig. 7b, the deposits show a reason-
ably regular size distribution in agreement with an instantaneous
nucleation–growth mechanism as determined by chronoampero-
metric studies.
+
rity does not interact with the Ag ions in solution to change its
speciation; however, the data presented in this study does not con-
clusively identify this relationship. Regardless of the nature of the
water interaction, it is suggested that control of water impurity in
this IL can allow experimental control over the type of morphology
obtained upon deposition. Unfortunately, the data obtained for the
[
BMIm][BF ] did not show any evidence for progressive nucleation,
In the case of [BMIm][BF ] (Fig. 7c), it can be seen that a fairly
4
4
thus it is difficult to know if the trends observed for wet and dry
C4mPyr][TFSI] are indicative of IL behaviour in general or if this is
unique to [C mPyr][TFSI].
uniform particle size distribution is observed on the GC electrode
surface. The silver deposits in spherical particulates of which there
is an underlying layer of spheres of 100–300 nm in diameter, upon
which larger deposits have grown due to the high overpotential
applied (Fig. 7d). Again this behaviour is complimentary to the CA
data which suggests that the mechanism is instantaneous nucle-
ation and growth in nature.
[
4
3.3. SEM and XRD characterisation of electrodeposits
Scanning electron microscopy (SEM) images were recorded to
characterise the silver electrodeposits formed from both IL systems
Because the silver deposition mechanism is strongly related to
the water content of the [C4mPyr][TFSI], SEM images were recorded
for both the dry and wet cases. In the dry [C4mPyr][TFSI] SEM
images (Fig. 7e and f) show that the deposited particle size does
not vary substantially, which is in agreement with an instanta-
neous nucleation–growth mechanism. The anisotropic nature of
the particles formed is interesting and suggests that the IL may be
acting as a growth directional agent, as seen for many organic sur-
factants [35,36] and inorganic salts [37] that have been employed
as additives in electroplating metals. Generally these additives
bind preferentially to certain crystal facets that inhibit or promote
growth in particular directions, which may also be the case in the
present study.
and 0.10 M KNO /water after the electrochemical measurements.
3
To allow for meaningful comparisons between all the systems
studied, the charge passed during the electrodeposition process
−2
was kept constant (90 mC cm ). In the case of the aqueous sys-
tem, since the chronoamperometry data suggested a change in
mechanism as a function of reduction potential, two deposition
potentials were chosen to encompass both regions to further probe
the impact of the electrodeposition mechanism on the deposition
morphology.
Fig. 7 shows typical SEM images of silver (confirmed by EDX
analysis) electrodeposited from [BMIm][BF ], [C mPyr][TFSI] and
4
4
0
.10 M KNO /water. Fig. 7a shows an SEM image of deposits
3

A. Basile et al. / Electrochimica Acta 56 (2011) 2895–2905
2905
If the silver deposition is carried out in [C mPyr][TFSI] that has
that the uptake of atmospheric water in the IL resulted in a change
in the electrodeposition mechanism to progressive nucleation and
growth. This is in agreement with studies carried out in aque-
ous solution that also demonstrated the same electrodeposition
mechanism. Interestingly, continuous exposure of the silver salt/IL
solution to atmospheric conditions resulted in the extensive for-
mation of silver nanoparticles that interfere with electrodeposition
experiments by adhering to the glassy carbon electrode. Overall it
has been demonstrated from these studies that the water content
of ionic liquids can significantly influence metal electrodeposition
processes and under controlled conditions may offer a route to
tuning the morphology of the resulting deposits.
4
been allowed to absorb atmospheric H O, the SEM images (Fig. 7g
2
and h) show significant differences to the dry case. The SEM images
show a random distribution of spherical particles from sub micron
sized upwards. All of the larger structures are layered on top of an
underlying layer of sub-micron sized spherical particles similar to
the case of [BMIm][BF ]. The particle size distribution behaviour is
4
consistent with the proposed change in mechanism from instanta-
neous to progressive nucleation and growth as suggested by the CA
data. The effect of water in this system can clearly have a significant
effect on the deposition morphologies.
XRD studies were carried out to investigate if the morphology
of the electrodeposits was related to any preferred crystallographic
orientation of the silver particles. For silver electrodeposited from
References
[
2
BMIm][BF ] at a potential of −0.80 V characteristic peaks at
4
◦
◦
◦
[1] F. Endres, D. MacFarlane, A. Abbott, Electrodeposition from Ionic Liquids, Wiley-
VCH, Weinheim, 2008.
ꢅ = 38.2 , 64.5 and 81.4 are observed due to the {1 1 1}, {2 2 0}
and {2 2 2} crystal planes of polycrystalline silver, respectively,
with a marked increase in intensity of the {1 1 1} plane compared
to the other planes (Fig. 8). The underlying GC substrate provides
its own XRD pattern which is indicated in Fig. 8. In the case of silver
electrodeposited from aqueous solution a similar XRD pattern was
obtained with an intense {1 1 1} reflection. In contrast, in the case of
[
2] W. Simka, D. Puszczyk, G. Nawrat, Electrochim. Acta 54 (2009) 5307.
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485.
9
[
[
4] S. Zein El Abedin, F. Endres, Electrochim. Acta 54 (2009) 5673.
5] G. Martínez-Casta n˜ ón, N. Ni n˜ o-Martínez, F. Martínez-Gutierrez, J. Martínez-
Mendoza, F. Ruiz, J. Nanopart. Res. 10 (2008) 1343.
[6] C.-N. Lok, C.-M. Ho, R. Chen, Q.-Y. He, W.-Y. Yu, H. Sun, P.K.-H. Tam, J.-F. Chiu,
C.-M. Che, J. Biol. Inorg. Chem. 12 (2007) 527.
dry [C mPyr][TFSI] the {1 1 1} peak is less intense when compared
4
[
[
7] C.A. Zell, F. Endres, W. Freyland, Phys. Chem. Chem. Phys. 1 (1999) 697.
8] F. Endres, W. Freyland, J. Phys. Chem. B 102 (1998) 10229.
to the {2 2 0} crystal plane. However, when atmospheric water was
present in [C mPyr][TFSI] a significant increase in intensity of the
[9] X.H. Xu, C.L. Hussey, J. Electrochem. Soc. 139 (1992) 1295.
10] F. Endres, W. Freyland, B. Gilbert, Ber. Bunsen-Ges. 101 (1997) 1075.
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806.
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C102.
14] S. Arimoto, H. Kageyama, T. Torimoto, S. Kuwabata, Electrochem. Commun. 10
4
[
[
[
{
1 1 1} crystal plane in particular is observed that is similar to the
XRD pattern obtained for the silver electrodeposit from aqueous
solution. This further indicates the role that adventitious water
plays in influencing the morphology and crystallography of the
silver electrodeposit.
[
[
(
2008) 1901.
[
[
[
15] M.-C. Tsai, D.-X. Zhuang, P.-Y. Chen, Electrochim. Acta 55 (2010) 1019.
16] A.I. Bhatt, A.M. Bond, J. Electroanal. Chem. 619 (2008) 1.
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Phys. Chem. A 114 (2010) 3744.
4
. Conclusions
The electrodeposition of silver onto glassy carbon electrodes
[
18] G.A. Snook, A.S. Best, A.G. Pandolfo, A.F. Hollenkamp, Electrochem. Commun.
was investigated in aqueous media and two different ionic liquids,
C mPyr][TFSI] and [BMIm][BF ]. The voltammetric data obtained
1405 (2006) 8.
[
4
4
[
19] D.J. Schiffrin, J. Electroanal. Chem. 199 (1986) 201.
shows for all three systems that electrodeposition of Ag proceeds
via a nucleation and growth type mechanism. In the case of the
aqueous system, the data shows that the removal of silver from the
glassy carbon electrode after plating is not chemically reversible
and trace silver always remains, presumably due to the forma-
tion of silver oxide. However, in the case of the ILs, close to
full reversibility is observed and no additional reactions of the
[20] A.R. Harris, A.K. Neufeld, A.P. O’Mullane, A.M. Bond, R.J.S. Morrison, J. Elec-
trochem. Soc. 152 (2005) C577.
[
21] W. Obretenov, T. Kossev, V. Bostanov, E. Budevski, J. Electroanal. Chem. 159
1983) 257.
(
[22] V. Bansal, V. Li, A.P. O’Mullane, S.K. Bhargava, CrystEngCommun 12 (2010) 4280.
[23] A.I. Bhatt, A. Mechler, L.L. Martin, A.M. Bond, J. Mater. Chem. 2241 (2007) 17.
[
[
24] I. Pastoriza-Santos, L.M. Liz-Marzan, Langmuir 2888 (2002) 18.
25] A. O’Mahony, D.S. Silvester, L. Aldous, C. Hardacre, R.G. Compton, J. Chem. Eng.
Data 2884 (2008) 53.
deposited silver are observed. The voltammetry for [C mPyr][TFSI]
is further complicated when water from atmospheric absorption
[26] M.O. Kestner, A.L. Allred, J. Am. Chem. Soc. 94 (1972) 7189.
4
[
[
27] M. Pazicky, F. Rominger, M. Limbach, Acta Cryst. E 66 (2010) m724.
28] D. Sroczynski, A. Grzejdziak, J. Incl. Phenom. Macrocyclic Chem. 42 (2002) 99.
red
is present. Under these conditions a significant shift in E
and
p
[29] B. Scharifker, G. Hills, Electrochim. Acta 879 (1983) 28.
[30] A.I. Bhatt, A.M. Bond, J. Zhang, J. Solid State Electrochem. 1593 (2007) 11.
[31] C.L. Hussey, X. Xu, J. Electrochem. Soc. 1886 (1991) 138.
ox
E
is observed; this effect is attributed to silver nanoparticle for-
p
+
mation from the reaction of dissolved Ag ions with water. The
formation of nanoparticles has been confirmed by UV/vis spec-
troscopy, EDX analysis and TEM images. In the case of the ILs, it was
found that the electrodeposition mechanism proceeded through an
instantaneous nucleation–growth mechanism as deduced by anal-
ysis of chronoamperometry data and confirmed by SEM imaging.
[
[
32] A. Milchev, E. Vassileva, V. Kertov, J. Electroanal. Chem. 107 (1980) 323.
33] Y. Cao, A.C. Wert, J. Electrochem. Soc. 149 (2002) C223.
[34] G.A. Gunawardena, G.J. Hills, I. Montengro, Electrochim. Acta 693 (1978) 23.
[
[
[
35] M.S. El-Deab, T. Sotomura, T. Ohsaka, Electrochim. Acta 52 (2006) 1792.
36] D. Romanska, M. Mazur, Langmuir 19 (2003) 4532.
37] B. Plowman, S.J. Ippolito, V. Bansal, Y.M. Sabri, A.P. O’Mullane, S.K. Bhargava,
Chem. Commun. (2009) 5039.
Significantly, for the case of [C mPyr][TFSI], it was demonstrated
4