Online Supplementary Material
Redox-induced solid-solid state transformation of tetrathiafulvalene (TTF)
microcrystals into mixed-valence and π-dimers in the presence of nitrate anions
Shaimaa M. Adeel, Lisandra L. Martin, Alan M. Bond
School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
1
Figure S1 Cyclic voltammograms (1st to 50th cycles of potential) obtained over the potential
range 200-250 mV at a scan rate of 50 mV s-1 with a drop-cast TTF-modified GC electrode in
contact with an aqueous 1.0 M Co(NO3)2 electrolyte.
Influence of the electrode material on Process I
Figure S2 shows cyclic voltammograms obtained (10th cycle of potential) using a TTFmodified (drop cast) at GC (3 mm diameter), Au (1.6 mm diameter), Pt (1.6 mm diameter)
and ITO (area 0.09 cm2) electrodes each immersed in 1.0 M aqueous Co(NO3)2 solutions. In
each case, the potential is initially scanned in the positive direction from -200 to 250 mV at
scan rate of 20 mV s-1. Table S1 summarizes the peak potential parameters of interest derived
from Figure S2. The electrode independent nature of these data indicates that the underlying
electrode substrate has no significant effect on the voltammetry, thereby suggesting that rate
determining nucleation–growth reaction does not include interaction with the electrode.13
2
Figure S2 Cyclic voltammograms obtained at a scan rate of 20 mV s-1 with a drop-cast TTFmodified different electrode materials in contact with an aqueous 1M Co(NO3)2 electrolyte.
Table S1 Voltammetric parameters obtained at a scan rate of 20 mV s-1 when TTF is
immobilized by drop casting onto different electrode materials that are then placed in contact
with 1 M an aqueous Co(NO3)2 electrolyte.
Electrode
material
Geometric
Area, cm2
𝑬𝒐𝒙𝟏
𝒑
mV
𝑬𝒓𝒆𝒅𝟏
𝒑
mV
𝑬𝒎𝟏
mV
∆𝑬𝒑𝟏
mV
GC
0.07
180
2
91
178
Au
0.02
186
2
94
184
Pt
0.02
180
5
91
178
ITO
0.09
180
2
91
178
3
Effect of electrolyte cation on Process I
Cyclic voltammograms (10th cycle) with a TTF-modified GC electrode (drop casting) in
contact with 0.1 M aqueous Co(NO3)2, Mg(NO3)2, Ni(NO3)2, Zn(NO3)2, Mn(NO3)2, 0.2 M
KNO3 and 0.2 M NaNO3 are shown in Figure S3. The similarity of the voltammetric
responses suggests that the electrolyte cation does not play a significant role in the kinetics or
thermodynamics of the solid-solid state transformation. Table S2 summarizes the
voltammetric parameters obtained from the data shown in Figure S3. The relatively constant
∆𝐸𝑝 and 𝐸𝑚1 values implies that the nucleation-growth mechanism only involves
incorporation and exclusion of the nitrate anion entering/leaving the lattice of TTF
microcrystals. However, from the stability of current viewpoint (the rate of attenuation of
voltammetric peak currents with increasing number of cycles of potential) the electrolyte
containing the Co2+ cation gave the most persistent response. Therefore, this electrolyte cation
was used in electrochemical synthesis studies aimed at characterizing oxidized TTF-NO3
based materials. The substantial differences in peak area is mainly attributable to variability
in the amount of TTF attached to the surface when using the drop cast method. Additionally,
the solubility of the TTF-NO3 based product apparently varies with the electrolyte counter
cation.
4
Figure S3 Cyclic voltammograms (10th cycle) obtained at a scan rate of 20 mV s-1 with a
drop-cast TTF-modified GC electrode in contact with 0.1 M an aqueous solution of
Co(NO3)2, Mg(NO3)2, Ni(NO3)2, Zn(NO3)2, Mn(NO3)2, 0.2 M KNO3 and 0.2 M NaNO3.
Table S2 Voltammetric parameters obtained at a scan rate of 20 mV s-1 when TTF is
immobilized by drop casting onto a GC electrode and then placed in contact with aqueous
solution of a nitrate salt.
Cation of
nitrate salt
Concentration
M
𝑬𝒐𝒙𝟏
𝒑
mV
𝑬𝒓𝒆𝒅𝟏
𝒑
mV
𝑬𝒎𝟏
mV
∆𝑬𝒑𝟏
mV
Zn2+
0.1
254
26
140
228
Mg2+
0.1
248
20
134
228
Mn2+
0.1
224
42
133
182
Co2+
0.1
257
31
126
196
Ni2+
0.1
254
16
135
238
K+
0.2
230
36
133
194
Na+
0.2
240
28
134
212
5
Figure S4 Plots of 𝐸𝑝𝑜𝑥1 , 𝐸𝑝𝑟𝑒𝑑1 and 𝐸𝑚1 versus log [NO3-] obtained with a TTF-modified GC
electrode in contact with aqueous Co(NO3)2 electrolyte at a scan rate of 20 mV s-1.
6
Voltammetric evidence for nucleation-growth kinetics for Process I
The scan rate effect
Figure S5 shows voltammograms obtained (10th cycle) with a TTF-modified GC electrode
(drop cast) in contact with a 1.0 M Co(NO3)2 aqueous solution as a function of scan rate,
while the voltammetric parameters obtained from these data are summarized in Table S3.
With increasing scan rate, 𝐸𝑝𝑜𝑥1 becomes more positive while 𝐸𝑝𝑟𝑒𝑑1 shifts to more negative
potentials. Thus, ∆𝐸𝑝1 increases with scan rate, while 𝐸𝑚1 is only slightly affected. The scan
rate dependence is consistent with a nucleation-growth process9.
Figure S5 Cyclic voltammograms (10th cycle) obtained at the designated scan rates with a
drop-cast TTF-modified GC electrode in contact with aqueous 1.0 M Co(NO3)2 electrolyte.
7
Table S3 Voltammetric parameters (10th cycle) obtained with a drop-cast TTF-modified GC
electrode in contact with aqueous 1.0 M Co(NO3)2 electrolyte as a function of scan rate.
𝑬𝒐𝒙𝟏
𝒑
𝑬𝒓𝒆𝒅𝟏
𝒑
𝑬𝒎𝟏
∆𝑬𝒑𝟏
10
mV
177
mV
5
mV
91
mV
172
20
180
2
91
178
30
185
1
93
184
40
189
-1
94
190
50
192
-3
94
195
60
194
-4
95
198
75
198
-5
96
203
100
208
-9
99
217
𝑺𝒄𝒂𝒏 𝑹𝒂𝒕𝒆 mV
s-1
8
The effect of switching potential
Figure S6 represents cyclic voltammogram obtained at a scan rate of 10 mV s-1 with drop-cast
TTF-modified GC electrode in contact with 0.1 M aqueous Co(NO3)2 when the potential is
switched at 190 mV, which corresponds to the foot of the oxidation process. When the
potential is switched shortly after detection of the onset of the oxidation of TTF, a current
loop is observed with a zero current crossover potential at 135 mV. This phenomenon is
highly characteristic of nucleation-growth kinetics.9, 21
Figure S6 Cyclic voltammogram obtained with a drop-cast TTF-modified GC electrode in
contact with aqueous 0.1 M Co(NO3)2 electrolyte at a scan rate of 10 mV s-1, when the
potential was switched at 190 mV.
9
Chronoamperometric evidence for nucleation-growth kinetics for Process I
Double-potential step chronoamperometry (DPSCA) experiments are also useful in
establishing the presence of nucleation-growth mechanisms.9,19-21 Figure S7a illustrates the
results of a DPSCA experiment for a TTF-modified GC electrode in contact with a 0.1 M
aqueous solution of Co(NO3)2 previously subjected to 10 cycles of potential over the range of
-200 - 350 mV vs. Ag/AgCl at a scan rate of 20 mV s-1. The potential was initially held at 400 mV for 10 seconds, where TTF is electroinactive. The potential was then stepped to 260
mV for 30 seconds to oxidize TTF to TTF+•. The potential was then stepped back to 30 mV
for 30 seconds to induce reduction of solid (TTF)2NO3 to solid TTF, accompanied by egress
of NO3- anions into solution phase. After each potential step, the current–time transient shows
the expected response; initial charging current spike, which rapidly decays toward a zero
followed by the appearance of well-defined Faradic current. The detection of current maxima
in current–time curves (Figure S7) is strong proof for nucleation-growth kinetics in both the
oxidation and reduction solid-solid state transformations.2b,3,5 Figure S7b shows the results of
DPSCA experiment under the same potential step conditions as for Figure S7a except that the
potential was stepped from -400 mV to designated potentials that introduce oxidation of solid
TTF, while Figure S7c shows the results of DPSCA as in (a) but with the potential being
stepped from -400 mV to 260 mV and then returned back to a designated reduction potential.
As expected, for the nucleation–growth mechanism, maxima are observed for oxidation and
reduction processes, respectively.
10
Figure S7 Double–potential step chronoamperograms obtained after a drop-cast TTFmodified GC electrode in contact with a 0.1 M aqueous solution of Co(NO3)2 is cycled 10
times over the potential range -400 to 350 mV then: (a) potential initially held at -400 mV for
10 seconds, then stepped to 260 mV for 30 seconds and finally back to 30 mV for 30 seconds,
(b) as in (a) but potential stepped from -400 mV to 260, 240, 220, 200, 190, and 180 mV (c)
same conditions as in (a), but with the second potential step set to designated potentials.
11
Schematic representation of the mechanism for nucleation-growth
Figure S8 Schematic representation of the nucleation-growth processes associated with
oxidation of a TTF-modified electrode in aqueous NO3− and reduction of the oxidized solid
back to TTF.
12
Voltammetric studies on the second oxidation process (Process II)
Role of electrode material
Voltammetric characteristics obtained from TTF-modified GC, metallic and semiconducting
(ITO) electrodes in contact with 1M aqueous Co(NO3)2 (Figure S9) are almost identical for
both processes I and II. Data in Table S4 summarizes voltammetric parameters obtained for
both processes and verifies that the underlying electrode material has no significant impact.
Figure S9 Cyclic voltammograms obtained over the potential range of -200 to 450 mV at a
scan rate of 20 mV s-1 from a drop-cast TTF-modified ITO, GC, Pt and Au electrodes in
contact with aqueous 1.0 M Co(NO3)2 electrolyte.
13
Table S4 Voltammetric parameters obtained when TTF is immobilized by drop casting onto
ITO, GC, Pt and Au electrodes which are then placed in contact with 1.0 M aqueous
Co(NO3)2 electrolyte and the potential is then scanned over the potential range of -200 to 450
mV at a rate of 20 mV s-1.
Electrode
material
Geometric
Area, cm2
𝑬𝒐𝒙𝟏
𝒑
mV
𝑬𝒓𝒆𝒅𝟏
𝒑
mV
𝑬𝒎𝟏
mV
∆𝑬𝒑𝟏
mV
GC
0.07
170
-9
80
179
Au
0.02
170
-9
80
179
Pt
0.02
170
-9
80
179
ITO
0.09
172
-10
80
179
𝑬𝒐𝒙𝟐
𝒑
mV
𝑬𝒓𝒆𝒅𝟐
𝒑
mV
𝑬𝒎𝟐
mV
∆𝑬𝒑𝟐
mV
395
300
347
95
393
300
346
93
393
300
376
93
395
300
347
95
14
The effect of the electrolyte cation on the voltammetry of solid TTF (Processes I and II)
Cyclic voltammogram obtained with 0.1 M aqueous Co(NO3)2 Mg(NO3)2, Ni(NO3)2,
Zn(NO3)2, Mn(NO3)2, KNO3 and aqueous electrolytes (Figure S10) and data in Table S5
reveal that there is a constant different between Em values for processes I and II. Thus, the
identity of the cation plays only a small role in the solid-solid transformation of either the first
or second oxidation processes.
Figure S10 Cyclic voltammograms (10th cycle) obtained with a drop-cast TTF-modified GC
electrode in contact with 0.1 M aqueous solutions of Co(NO3)2, Mg(NO3)2, Ni(NO3)2,
Zn(NO3)2, 0.2 M KNO3 and 0.2 M NaNO3 at a scan rate of 50 mV s-1 when the potential is
scanned over the range of -150 to 580 mV.
15
Table S5 Parameters obtained from voltammograms shown in Figure 11 (main paper) when
TTF immobilized by drop casting onto GC electrode and in contact with aqueous solutions of
designated nitrate salts.
Cation of
nitrate salt
Concentration
M
𝑬𝒐𝒙𝟏
𝒑
mV
𝑬𝒓𝒆𝒅𝟏
𝒑
mV
𝑬𝒎𝟏
mV
∆𝑬𝒑𝟏
mV
𝑬𝒐𝒙𝟐
𝒑
mV
𝑬𝒓𝒆𝒅𝟐
𝒑
mV
𝑬𝒎𝟐
mV
∆𝑬𝒑𝟐
mV
Zn2+
0.1
258
11
134
247
459
330
394
129
Na+
0.2
245
72
158
173
456
390
423
66
Co2+
0.1
212
10
111
202
440
332
386
108
Ni2+
0.1
228
3
215
225
439
314
376
125
K+
0.2
228
28
128
200
447
347
397
100
Mg2+
0.1
264
64
164
200
499
395
447
104
16
Scan rate effect (Process II)
For process II, cyclic voltammograms for a TTF-modified GC in contact with 1.0 M
Co(NO3)2 as the aqueous electrolyte (Figure S11) gave the data in Table S4 by varying the
scan rate. The dependence of 𝐸𝑝𝑜𝑥2 , 𝐸𝑝𝑟𝑒𝑑2 and ∆𝐸𝑝2 on scan rate was similar to that for
process I, while 𝐸𝑚2 is unaffected.
Figure S11 Cyclic voltammograms obtained at designated scan rates with a drop-cast TTFmodified GC electrode in contact with aqueous 1.0 M Co(NO3)2 electrolyte when the
potential is scanned over the range of -200 to 470 mV.
17
Table S6 Voltammetric parameters obtained with a drop-cast TTF-modified GC electrode in
contact with aqueous 1.0 M Co(NO3)2 electrolyte as a function of scan rate.
Scan Rate
mV s-1
𝑬𝒐𝒙𝟏
𝒑
mV
𝑬𝒓𝒆𝒅𝟏
𝒑
mV
𝑬𝒎𝟏
mV
∆𝑬𝒑𝟏
mV
𝑬𝒐𝒙𝟐
𝒑
mV
𝑬𝒓𝒆𝒅𝟐
𝒑
mV
𝑬𝒎𝟐
mV
∆𝑬𝒑𝟐
mV
10
159
-5
77
161
387
305
346
82
20
177
-10
84
187
395
300
346
95
30
179
-14
82
193
398
295
346
106
40
187
-21
83
208
401
292
346
109
50
191
-23
84
214
402
290
346
111
60
195
-24
85
222
405
287
346
118
75
197
-27
85
224
409
284
346
125
100
209
-34
87
243
414
283
348
131
18
Switching potential effect (Process II)
Evidence for a nucleation and growth mechanism associated with process II was obtained
from the cyclic voltammetry via the observation of a current loop with a zero current
crossover potential of 375 mV when the potential was switched at the foot of the process
(Figure S12).
Figure S12 Cyclic voltammogram obtained with a drop-cast TTF-modified GC electrode in
contact with 0.1 M aqueous Co(NO3)2 electrolyte when the potential was switched at 390 mV
at a scan rate of 10 mV s-1.
19
Multiple cycling of potential effect (Processes I and II)
Figure S13 Cyclic voltammograms (1st to 50th cycle) obtained over the potential range of 200 - 450 mV at a scan rate of 50 mV s-1 with a drop-cast TTF-modified GC electrode in
contact with an aqueous 1.0 M Co(NO3)2 electrolyte.
20
Effect of electrolyte concentration on Processes I and II
Figure S14 Plots of 𝐸𝑝𝑜𝑥2 , 𝐸𝑝𝑟𝑒𝑑2 and 𝐸𝑚2 versus log [NO3-] obtained with a drop-cast, TTFmodified GC electrode in contact with aqueous Co(NO3)2 electrolyte at a scan rate of 20 mV
s-1.
Table S7 Voltammetric parameters obtained with a drop-cast TTF-modified GC electrode in
contact with designated concentrations of aqueous Co(NO3)2 electrolyte at a scan rate of 20
mV s-1.
𝑬𝒐𝒙𝟏
𝒑
𝑬𝒓𝒆𝒅𝟏
𝒑
𝑬𝒎𝟏
∆𝑬𝒑𝟏
𝑬𝒐𝒙𝟐
𝒑
𝑬𝒓𝒆𝒅𝟐
𝒑
𝑬𝒎𝟐
∆𝑬𝒑𝟐
mV
mV
mV
mV
mV
mV
mV
mV
1.00
170
-9
80
179
400
300
350
100
0.50
194
6
100
188
431
325
378
106
0.25
220
14
117
206
452
333
392
119
0.10
242
41
141
201
470
363
416
107
0.05
294
74
184
220
500
380
440
120
0.01
339
42
190
297
545
378
461
167
Concentration
M
21