Electrochemistry of Carbon Electrodes E-Book
151,99 €
Mehr erfahren.
- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Serie: Advances in Electrochemical Sciences and Engineering
- Sprache: Englisch
The book sets the standard on carbon materials for electrode design. For the first time, the leading experts in this field summarize the preparation techniques and specific characteristics together with established and potential applications of the different types of carbon-based electrodes. An introductory chapter on the properties of carbon together with chapters on the electrochemical characteristics and properties of the different modifications of carbon such as carbon nanotubes, graphene, carbon fiber, diamond or highly ordered pyrolytic graphite provide the reader with the basics on this fascinating and ubiquitous electrode material. Cutting-edge technologies such as carbon electrodes in efficient supercapacitors, Li-ion batteries and fuel cells, or electrodes prepared by screen-printing are discussed, giving a complete but concise overview about the topic. The clearly structured book helps newcomers to grasp easily the principles of carbon-based electrodes, while researchers in fundamental and applied electrochemistry will find new ideas for further research on related key technologies.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 966
Veröffentlichungsjahr: 2015
Ähnliche
Table of Contents
Cover
Advances in Electrochemical Science and Engineering
Title Page
Copyright
List of Contributors
Series Editors Preface
Preface
Chapter 1: Properties of Carbon: An Overview
1.1 Overview of Properties
1.2 Different Forms of Carbon
1.3 Outlook
References
Chapter 2: Electrochemistry at Highly Oriented Pyrolytic Graphite (HOPG): Toward a New Perspective
2.1 Introduction
2.2 Structure and Electronic Properties of HOPG
2.3 Formative Studies of HOPG Electrochemistry
2.4 Microscopic Views of Electrochemistry at HOPG
2.5 Conclusions
Acknowledgments
References
Chapter 3: Electrochemistry in One Dimension: Applications of Carbon Nanotubes
3.1 Carbon Nanotubes: General Considerations
3.2 Structure and Synthesis of CNTs
3.3 Structure of CNTs versus Electrochemical Properties
3.4 Strategies for the Preparation of Carbon Nanotube-Based Electrodes
3.5 Prospective Work
References
Chapter 4: Electrochemistry of Graphene
4.1 Overview of Graphene Properties
4.2 Preparation of Graphene
4.3 Capacitance of Graphene Electrodes
4.4 Electron Transfer Kinetics at Graphene Electrodes
4.5 Conclusion and Future Directions
References
Chapter 5: The Use of Conducting Diamond in Electrochemistry
5.1 Introduction
5.2 Electrode Geometries and Arrangements
5.3 Effect of Surface Termination on the Electrochemical Response of BDD
5.4 Polycrystalline Versus Single-Crystal Electrochemistry
5.5 Imparting Catalytic Activity on BDD
5.6 Chemical Functionalization of BDD Electrodes
5.7 Electroanalytical Applications of BDD
5.8 Conclusions
Acknowledgments
References
Chapter 6: Modification of Carbon Electrode Surface
6.1 Introduction
6.2 Covalent Modification
6.3 Noncovalent Modification
6.4 Future Directions
Acknowledgments
References
Chapter 7: Carbon Materials in Low–Temperature Polymer Electrolyte Membrane Fuel Cells
7.1 Introduction
7.2 Carbon as Support Material in Fuel Cell Electrocatalysts
7.3 Carbon as Catalytically Active Component in Fuel Cells
7.4 Carbon as Structure-Forming Element in Porous Fuel Cell Electrodes
7.5 Summary and Outlook
Acknowledgments
References
Chapter 8: Electrochemical Capacitors Based on Carbon Electrodes in Aqueous Electrolytes
8.1 Introduction
8.2 Fundamentals on Carbon/Carbon Electrical Double-Layer Capacitors
8.3 Carbons and Electrolytes for Electrical Double-Layer Capacitors
8.4 Attractive Electrochemical Capacitors in Aqueous Solutions
8.5 Conclusions and Perspectives
References
Chapter 9: Carbon Electrodes in Electrochemical Technology
9.1 Introduction
9.2 Comments on the Carbons Met in Electrochemical Technology
9.3 Manufacture of Chemicals
9.4 Water and Effluent Treatment
9.5 Flow Batteries
References
Chapter 10: Carbon Electrodes in Molecular Electronics
10.1 Introduction
10.2 Fabrication
10.3 Novel Allotropes of Carbon in Molecular Electronics
10.4 Charge Transport
10.5 Conclusions and Prospects
Acknowledgments
References
Chapter 11: Carbon Paste Electrodes
11.1 Introduction: Carbon Paste Electrodes – The State of the Art
11.2 Carbon Paste as the Electrode Material
11.3 Modified Carbon Paste Electrodes
11.4 Latest Achievements in Electroanalysis with CMCPEs and CP-Biosensors and Perspectives for the Future
References
Chapter 12: Screen-Printed Carbon Electrodes
12.1 Introduction
12.2 Conductivity of Composites
12.3 Carbon Polymorphs
12.4 Oxygen Functionalities
12.5 Activated Carbons
12.6 Binder–Solvent Combinations
12.7 PVDF Properties
12.8 PVDF Solubility
12.9 Flexible Substrates
12.10 Screen Printing Process
12.11 Screen Printing Materials
12.12 Ink Flow
12.13 Substrate Wetting
12.14 Commercial Ink Additives
12.15 Binder Percentage
12.16 Multilayered Electrodes
12.17
IR
Drop
12.18 Areal Capacitance
12.19 Equivalent Circuit
References
Index
End User License Agreement
Pages
xiii
xiv
xv
xvi
xvii
xix
xxi
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
445
446
447
448
449
Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: Properties of Carbon: An Overview
Figure 1.1 Control of the graphene plasmon resonance frequency by electrical gating and microribbon widths. (a) AFM (atomic force microscopy) images of graphene microribbons with widths of 1, 2, and 4 µm. Color bar of the height is shown on the right. (b) Fermi energy (
E
F
) dependence of the graphene plasmon frequency (top axis gives related dependence on charge density |
n
|
1/2
) of ribbons with three different widths.
Figure 1.2 Universal light absorbance and optical conductivity of graphene. (a) Schematic of Dirac-cone and interband optical transitions in graphene. (b) Optical absorbance (left axis) and optical sheet conductivity (right axis) of three graphene samples. The spectral range is from 0.5 to 1.2 eV. The black horizontal line shows the universal absorbance value of 2.293% per layer, with the variation within 10%. (c) The optical absorbance of graphene Sample 1 and Sample 2 over a smaller spectral range from 0.25 to 0.8 eV.
Figure 1.3 Raman spectrum of graphene at 0 V (applied bias voltage), excited by a 2.33 eV laser radiation, in an electrochemical environment. The asterisks (*) indicate Raman bands of the electrolyte.
Figure 1.4 The Raman scattering processes of the G, D, D′, and G′ bands of graphene.
Figure 1.5 Raman spectra of the G′ band of graphene with different numbers of layers. The excitation laser wavelength is 514 nm.
Figure 1.6 The schematic illustration of an experimental setup of
in situ
Raman spectroelectrochemistry. The sample (
12
C/
13
C bilayer graphene in this sketch) is on the substrate with ionic gating (light grey cylinders), with two electrode probes made of Ag and Pt. The back gating is through the Au metal electrode. The setup is placed under the Raman spectrometer to achieve
in situ
Raman spectroscopy.
Figure 1.7 The change of D band with electrochemical doping. (a) Raman spectra of defective graphene at different Fermi energies (
E
F
), measured under 633 nm laser excitation. (b) The normalized intensity of the D band as a function of Fermi level, or charge carrier concentration at 514 and 633 nm laser excitations.
Figure 1.8
In situ
Raman spectroelectrochemistry data for the G and G′ bands of graphene excited by 2.33 eV laser irradiation. The heavy black trace is for
V
= 0 applied voltage.
Figure 1.9 The Raman spectra of bilayer graphene with the two layers of:
13
C/
12
C, both
13
C, and both
12
C. The graphene with the
13
C isotope has red-shifted G and G′ peaks, compared to
12
C graphene.
Figure 1.10 Energy band diagram and density of states (DOS) of a carbon nanotube. The 1D van Hove singularities give a high DOS at well-defined energies.
Figure 1.11 (a) A carbon nanotube defined by the chiral vector , which is perpendicular to the nanotube axis. Here, is the chiral angle, and and are the unit vectors of graphene. (b) Possible chiral vectors (n, m) of carbon nanotubes (see text). Different (n, m) chiralities result in different physical properties, including metallic (large dots) and semiconducting (small dots) nanotubes.
Figure 1.12 Three types of carbon nanotubes: (a) armchair, (b) zigzag, and (c) chiral. The definition of nanotube types is according to the orientation perpendicular to the nanotube axis.
Figure 1.13 (a) Raman spectra of the G band at several potentials applied to a SWCNT bundle. (b,c) Variation of the G+ band and G− band frequency, respectively, with the applied potential for three different electrolyte solutions.
Figure 1.14 Kataura plot [81–83], showing the relationship between electronic transition energies and the SWCNT diameters. Each point on the plot shows an optically allowed electronic transition energy
E
ii
, which is the energy separation between van Hove singularities in the conduction band to the valence band. Crosses represent semiconducting SWCNTs (labeled “S”) and circles represent metallic SWCNTs (labeled “M”).
Figure 1.15 Variation of the C−C bond length (estimated from G band variation) with electrochemical charge transfer (
f
c
) induced on the nanotubes.
Figure 1.16 GNRs with different chiral orientations: zigzag and armchair.
Figure 1.17 Development of edge structures in graphene nanoribbons using Joule heating inside a TEM (transmission electron microscope). (a) Graphene nanoribbon with zigzag–armchair edges. The black arrows indicate the junction between zigzag and armchair edges. With the increased time of Joule heating (a–d), the zigzag-armchair junction position moves. The sketches on the left and right of the TEM images (a–d) indicate the graphene nanoribbon structures before and after Joule heating, respectively. Scale bar in (a): 2 nm.
Figure 1.18 Unzipping a carbon nanotube to form a graphene nanoribbon.
Chapter 2: Electrochemistry at Highly Oriented Pyrolytic Graphite (HOPG): Toward a New Perspective
Figure 2.1 (a) Schematics of the graphite crystal structure of AB-stacked graphite and the corresponding Brillouin zone of bulk graphite, together with the labels for special symmetry points. (b) Side views for Bernal (ABA) stacking (left) and rhombohedral (ABC) stacking (right).
Figure 2.2 Atomic resolution STM images of the surface of (a) graphite and (b) graphene. While the graphite surface shows a triangular structure, the graphene surface exhibits the honeycomb structure with all six atoms in the hexagon vertices visible.
Figure 2.3 AFM images of freshly cleaved HOPG surfaces of different grades, highlighting the significant differences in topographical structure. Note the differences in scale bars (lateral and height).
Figure 2.4 (a) AFM images of BPPG and (b) Scanning electron microscopy images of EPPG at different magnifications.
Figure 2.5 Raman spectra acquired on different HOPG grades ((a) AM and (b) SPI-3, (c) BPPG, and (d) EPPG).
Figure 2.6 (a) Graphite electronic band structure along high-symmetry lines in the Brillouin zone. (b) Electronic DOS of graphite. (c) Curves representing the DOS for pyrolytic graphite determined by Gerischer using capacitance measurements, compared with the curves obtained by the SWMcC and JD models for energy bands near the
H
-
K
axis.
Figure 2.7 (a) STM images and STS spectra near monoatomic steps of an HOPG sample with zigzag edge (top) and armchair edge (bottom). The color key on the spectra assigns the lateral distance of the tip from the step edge. (b) STS spectra of graphene and graphite, showing a finite differential conductance at the neutrality point for graphite, consistent with the finite DOS.
Figure 2.8 (a–d) Set of STM images and (e–h) the corresponding STS spectra of HOPG samples that exhibit Moire patterns due to the existence of a twist angle (indicated) between the top graphene layer and the layer immediately underneath.
Figure 2.9 (a)(i) Raman spectra of laser-treated HOPG (three pulses, 50 MW cm
−2
): (A) off the laser and (B) on the laser spot. (a)(ii) Corresponding CVs of Fe(CN)
6
3−/4
−
(1 M KCl), 200 mV s
−1
, on untreated (upper curve) and laser-treated (lower curve) AM-grade HOPG. (b)(i) Raman spectra obtained in air after electrochemically pretreating HOPG for 2 min in 0.1 M KNO
3
solution at different potentials, 1565 cm
−1
peak is dioxygen: (A) 1.6 V; (B) 1.85 V; and (C) 1.95 V vs Ag/AgCl. (b)(ii) Corresponding CVs of Fe(CN)
6
3−/4
−
(1 M KCl), 200 mV s
−1
on AM-grade HOPG after 1.85 V electrochemical pretreatment (ECP) (upper curve) and 1.95 V ECP (lower curve). The intensity of the Raman D band, which indicates edge and defect sites, yields comparable results for the two surface activation procedures, laser activation and ECP, with ECP generating more surface oxides than laser activation.
Figure 2.10 Log–log plot of
k
0
for “validated” AM-grade HOPG (triangle) and laser-activated GC (circles) versus
k
exc
for eight redox couples. The horizontal line indicates the instrumental limit for
k
0
determination, the dashed line is the least-square fit for the HOPG data, with slope = 0.29 and the solid line is from the proposed simple form of the relationship between
k
0
and
k
exc
predicted by Marcus theory. Redox systems are (1) IrCl
6
2−/3−
, (2) Ru(NH
3
)
6
3+/2+
, (3) Co(phen)
3
3+/2+
, (4) methyl viologen, (5) Fe(phen)
3
3+/2+
, (6) Fe(CN)
6
3−/4−
, (7) Co(en)
3
3+/2+
, and (8) Ru(en)
3
3+/2+
, where phen is phenanthroline and en is ethylenediamine.
Figure 2.11 (a) Observed
k
0
for Fe(CN)
6
3−/4−
, calculated from CV measurements with the Nicholson method [155] (inset shows same data with a logarithmic ordinate). (b) Observed capacitance,
C
0
, for laser-modified HOPG/aqueous electrolytes, determined from semi-integral voltammetry [154], as a function of laser activation power density. Each voltammogram was taken after cleavage of the HOPG surface and three 9 ns laser pulses in air.
Figure 2.12 (a) CVs recorded at EPPG and basal plane HOPG. (b) Comparison of the basal plane HOPG voltammograms with the best fit to linear diffusion CV simulations for the oxidation of 1 mM Fe(CN)
6
4−
(1 M KCl) at 1 V s
−1
.
Figure 2.13 CV for the reduction of 1 mM Fe(CN)
6
3−
in aqueous 0.1 M KCl solution at a scan rate of 75 mV s
−1
: (a) ZYH-grade HOPG electrode shows a highly irreversible process and (b) ZYH-grade HOPG electrode, which was hand-polished to create edge-plane defect sites, displays both a reversible and irreversible process. (c) Relationship of Δ
E
p
from CVs to the percentage of edge plane calculated from
k
0
(with two values indicated by ▴ and Δ) and
C
0
(▪). (d) The individual second to fifth harmonic peak currents (2–5 ω
t
) from AC voltammetry, with inset showing the closer view for the low-level edge-plane defect regions.
Figure 2.14 CVs for 1 mM Fe(CN)
6
3−/4−
redox couple: (a)(i) oxidation in 1 M KCl solution at 1.0 V s
−1
on AM-grade HOPG; (b)(i) oxidation in 1 M KCl solution at 1.0 V s
−1
on SPI-1-grade HOPG; and (c)(i) reduction in 0.1 M KCl solution at 75 mV s
−1
on ZYH-grade HOPG. (a)(ii)–(c)(ii) Corresponding AFM images of the HOPG surface showing typical step-edge densities and coverage for different grades of HOPG samples.
Figure 2.15 (a) Schematic of the SMCM setup, showing the one-electron oxidation of FA
+
to FA
2+
at a substrate electrode. (b) Simulations showing the influence of kinetics on SMCM CVs, for a pipette of 2 µm diameter and 7.5° taper angle. Black: Nernstian response. Kinetic cases use Butler–Volmer equations (
α
= 0.5). Red:
k
0
= 0.1 cm s
−1
, Green:
k
0
= 0.01 cm s
−1
, Blue:
k
0
= 0.001 cm s
−1
(5 mM redox species,
D
= 1 × 10
−5
cm
2
s
−1
),
η
is the overpotential. (c) Experimental (black) and simulated (Nernstian, green;
k
0
= 0.01 cm s
−1
,
α
= 0.5, red) CVs for a pipette of 580 nm diameter with a solution of 2 mM FA
+
(
D
= 6 × 10
−6
cm
2
s
−1
).
Figure 2.16 (a) Schematic of the simulation geometry model for a Nafion-coated HOPG surface (i), where the numbers are indicative of the film–solution interface (1), periodic boundaries from which the step array response can be determined (2a, 2b), step-edge plane (3), and basal plane (4a, 4b), respectively, and simulated concentration profiles for a Nafion-Ru(bpy)
3
2+
(
D
= 4.7 × 10
−11
cm
2
s
−1
) film at the half-wave potential from a CV at a scan rate of 10 mV s
−1
(ii, iii) and 1 V s
−1
(iv, v). The basal plane was assumed to be inert (
k
0
= 0 cm s
−1
; ii, iv) and active (
k
0
= 1 × 10
−4
cm s
−1
; iii, v), with the step-edge activity at
k
0
= 1 × 10
−4
cm s
−1
. CVs recorded at a scan rate of 0.5 V s
−1
on an SPI-1-grade HOPG surface, with a deposited thin Nafion film incorporating (b) Ru(bpy)
3
2+
and (c) Ru(NH
3
)
6
3+
, where the experimental data are shown in black, together with simulations with basal plane kinetics either reversible (red), inert (
k
0
= 0 cm s
−1
, green), or active with a rate constant of
k
0
= 1 × 10
−4
cm s
−1
for Ru(bpy)
3
2+
and
k
0
= 4.5 × 10
−5
cm s
−1
for Ru(NH
3
)
6
3+
(blue).
Figure 2.17 (a) Schematic of the SECCM setup and an scanning electron microscopy image of a typical tip employed. (b) SECCM maps for the electro-reduction of 2 mM Ru(NH
3
)
6
3+
on ZYA-grade HOPG, showing (i) topography, (ii) AC component of the conductance current, (iii) surface electroactivity, and (iv) a histogram of all the electroactivity (redox current) pixels with respect to the average activity. (c) SECCM surface electroactivity map (left) for 1 mM Ru(NH
3
)
6
3+
reduction at AM-grade HOPG, with both surface current (green) and barrel current (blue) shown for a typical line across several steps. (d) Surface electroactivity map for the oxidation of 2 mM Fe(CN)
6
4−
(i), with the average current of each line in the image shown in (ii). (e) Normalized linear sweep voltammograms for the oxidation of 2 mM Fe(CN)
6
4−
on fresh HOPG (black) and aged HOPG after 1 h exposure in air (blue), with a scan rate of 100 mV s
−1
.
Figure 2.18 (a) Schematic for feedback mode of SECM. SECM steady-state normalized current–distance approach curves with a gold disc ultramicroelectrode (UME) tip (radius 6 µm) for Fe(CN)
6
4−
reduction toward (b) HOPG and (c) glassy carbon, where
i
is the current and
i
(∞)
is the bulk current. The normalized distance is the absolute tip–substrate distance divided by the tip radius.
Figure 2.19 (a) Topographical and (b) current features on the surface of HOPG obtained from SECM–AFM, with the corresponding cross-sectional profile (c) and (d) along the line marked in (a) and (b), respectively. (e) Vertical deflection and (f) current response of the upper area of (a) and (b), and the numbers indicated are different support potentials, changing from the white line. (g) Simulation of SECM with a conical electrode, showing the current profiles across step 1 in (a). The experimental response (red line), the current response with a 100 times enhanced reaction rate at the step edge (blue line) and without enhanced reaction rate (green line). Note the small change in absolute current on the y-coordinate.
Figure 2.20 CVs for the oxidation of 1 mM Fe(CN)
6
4−
in 0.1 M KCl solution, at 0.1 V s
−1
, after a freshly cleaved HOPG (SPI-1) surface was left (a) in contact with solution or (b) in air, after cleavage for 0 min (black), 1 h (red), and 3 h (green), and (c) after leaving a sample in air for 24 h after cleavage.
Figure 2.21 Conductive AFM images (5 × 5 µm) of an HOPG (SPI-1) surface showing the (i) height and (ii) conductivity (a) immediately after cleavage and (b) 24 h after cleavage. The conductive AFM
i–V
curves shown were recorded on the terrace locations marked in (a)(ii) and (b)(ii).
Figure 2.22 (a) SECCM linear sweep voltammogram of the electro-oxidation of 100 μM DA (0.15 M phosphate buffered saline containing 150 mM NaCl (pH 7.2)). Maps of (b) surface activity, (c) DC conductance current, and (d) AC component of the conductance current obtained with SECCM setup, together with (e) an AFM image in the same area.
Figure 2.23 Macroscopic CVs for the oxidation of 1 mM DA (a)(i), (b)(i) and 1 mM EP (a)(ii), (b)(ii) on freshly cleaved surfaces of ZYA- and SPI-3-grade HOPG, at a scan rate of 0.1 V s
−1
.
Figure 2.24 (a) Schematic of the FSCV–SECCM setup where 10 sequential CV scans were carried out in each of a series of spots on an HOPG surface, with hold times of 50 ms, 100 ms, 250 ms, 0.5 s, 1 s, and 5 s between each CV. (b) FSCVs for the adsorption of 1 μM AQDS in 0.05 M HClO
4
solution, recorded at 250 ms intervals (hold time) with a scan rate of 100 V s
−1
, at AM-grade HOPG. (c) The fractional coverage of AQDS and corresponding charge in different parts of an AM-grade HOPG surface as a function of time, with respect to the different hold times. Solid line is the simulated behavior for diffusion-controlled adsorption. (d) Typical AFM image (
ex situ
) for an adsorption spot on an AM-grade HOPG surface taken after about 10 s, along with a 3 × 3 µm higher resolution image, with the approximate droplet footprint outlined in white. (e) Percentage of step edges found within six adsorption spots, where FSCV measurements were made (at different total adsorption time) and the observed fractional coverage of electroactive AQDS.
Figure 2.25 (a) Schematic showing the modification of an HOPG surface with an electrogenerated diazonium radical. (b) AFM image of the deposition array on HOPG. CVs of 0.1 mM diazonium in 50 mM H
2
SO
4
at the surface of (c) AM-grade and (d) SPI-3-grade HOPG at a scan rate of 0.2 V s
−1
.
Chapter 3: Electrochemistry in One Dimension: Applications of Carbon Nanotubes
Figure 3.1 (a) Schematic representation of the roll-up vector over the graphene surface, which defines the different CNT structures. (b) SWCNT armchair, zigzag, and chiral.
Figure 3.2 (a) TEM micrograph of as-synthesized SWCNT. (b) TEM micrograph of a sample containing both MWCNT and bCNT. (two magnifications are displayed at right and left panels, respectively).
Figure 3.3 Cyclic voltammograms in 1 mM over (a) covalently aligned and (b) drop-coated SWCNT-modified Au/cysteamine electrode. Supporting electrolyte: 0.05 M phosphate buffer solution pH 7.0 and 0.05 M KCl solution.
Figure 3.4 (a) Schematic representation of the procedure for preparing the CNT electrodes with tip exposed (CNT-T) or sidewall (CNT-S) accessible to electrolyte. CVs of 2.0 mM H
2
O
2
(b,c), and 2.0 mM ascorbic acid (d,e) recorded in phosphate buffer solution pH 6.5 at the CNT-S (upper curves in b and d), O-CNT-S (lower curves in b and d), CNT-T (upper curves in c and e), and O-CNT-T electrodes (lower curves in c,e). The dotted curves were recorded at the corresponding CNT electrodes in the absence of the electrochemical probe molecules. Scan rate: 0.100 V s
−1
.
Figure 3.5 Values of charge transfer resistance (
R
ct
) obtained by fitting with an equivalent circuit of the impedance spectra performed in for several electrodes (from left to right): EPPG, bCNT, SWCNT, MWCNT with diameter equal to 30, 50, and 140 nm, graphite and BPPG. The inset shows values at a lower resistance scale.
Figure 3.6 SEM micrographs of glassy carbon disks modified with different dispersions of MWCNT: (a) 1.00 mg ml
−1
MWCNT in 1.00 mg ml
−1
GOx solution prepared in 50 : 50 (v/v) ethanol/water; (b) 1.00 mg ml
−10
MWCNT in 1.00 mg ml
−1
PEI solution prepared in 50 : 50 (v/v) ethanol/water; (c) 1.00 mg ml
−1
bCNT in 100 ppm dsDNA solution prepared in 50 : 50 (v/v) ethanol/water (inset: bCNT in dsDNA solution prepared in water); and (d) 1.00 mg ml
−1
MWCNT in 0.25 mg ml
−1
Polyhis solution prepared in 75 : 25 (v/v) ethanol/acetate buffer solution pH 5.00 (inset: MWCNT in 2.00 mg ml
−1
Polyhis).
Figure 3.7 SECM surface plot images of (a) GCE/MWCNT-H
2
O, (b) GCE/MWCNT-DMF, (c) GCE/MWCNT-CHI, and (d) GCE/MWCNT-Naf modified with 1.0 mg ml
−1
of CNT dispersion. Experimental conditions: 5.0 × 10
−4
M FcOH solution in 0.050 M phosphate buffer pH 7.40. Image parameters: 1 µm s
−1
tip scan,
E
tip
= 0.500 V,
E
substrate
= 0.000 V.
Chapter 4: Electrochemistry of Graphene
Figure 4.1 Overview for the production methods of graphene [19].
Figure 4.2 A schematic to show the preparation of the ME graphene samples and transfer process [22].
Figure 4.3 Showing the experimental setup used by Liu
et al.
[34] for the electrochemical exfoliation of graphite.
Figure 4.4 Schematic of CVD-grown graphene on Ni and Cu substrates [54].
Figure 4.5 Capacitance–potential curves for the basal plane of stress-annealed graphite for a range of concentrations (0.9, 10
−1
, 10
−2
, 10
−3
, 10
−4
, and 10
−5
M from top to bottom) in NaF (pH = 6) [69].
Figure 4.6 Schematic of the electrode fabrication [3].
Figure 4.7 A comparison for the (a) calculated and (b) measured capacitance of monolayer graphene when either one or two sides are exposed to 4 M H
2
SO
4
electrolyte solution.
Figure 4.8
C
int
versus potential plots for electrodes prepared with one to five layers of graphene in a 6 M potassium hydroxide aqueous electrolyte [88].
Figure 4.9 Effect of n-doping on capacitance of graphene with various concentrations using 6 M potassium hydroxide aqueous electrolyte.
Figure 4.10 (a) Shape of the voltammetry for radial and linear diffusion. (b) Schematic diagram showing the development of the diffusion layer with increasing time (or charge passed), that is, from (i) to (iii).
Figure 4.11 Simulated dependence of the voltammetric shape (dimensionless current vs potential) on the domain size of a heterogeneous surface. The
k
0
of the “slow” and “fast” kinetics domains were 1 × 10
−4
cm s
−1
and 1 × 10
−2
cm s
−1
, respectively.
Figure 4.12 (a) Comparison of CVs obtained for open-edge graphene nanofibers (o-SGNFs) and folded-edge graphene nanofibers (f-SGNFs). Schematic and TEM micrographs of the (b) o-SGNF and (c) f-SGNF.
Figure 4.13 (a) Microelectrode-shaped voltammograms obtained on the graphene-decorated SAM Au electrode. (b) Schematic of the microelectrode fabrication.
Figure 4.14 (a) Schematic of the monolayer CVD graphene (grey, labelled) with induced defects (light grey zone with dashed outline) deposited on a Si/SiO
2
substrate (black). Panels (b) and (c) show SECM maps of the graphene with induced defects and the same area passivated using
o
-phenylenediamine electropolymerization, respectively.
Figure 4.15 (a) Schematic of the SECCM setup, (b) voltammetry obtained on a graphene surface. Scanned area with varied flake thicknesses of different light contrast and electrochemical activity is shown as (c) optical micrograph and (d) corresponding SECCM map. Panels (e) and (f) show correlation between the feedback current or HET rate and the light contrast (number of graphene layers), respectively.
Figure 4.16 Schematic of the edge-plane (a) and basal plane (b) monolayer graphene device, fabricated using poly(methyl methacrylate) (PMMA) and epoxy resin (ER).
Figure 4.17 (a) Schematic of the ME graphene monolayer electrode preparation. (b) Microelectrode voltammetric response obtained on mono-, bi-, and multilayer graphene flakes, normalized to the flake radius.
Figure 4.18 (a) Photograph and (b) the schematic of the micromanipulator setup used for deposition of liquid microdroplets on the surface of graphene electrodes.
Figure 4.19 (a,b) Scanning electron micrographs, (c) transmission electron micrograph, and (d) electron diffraction pattern of the “3D graphene” catalyst. Panels (e) and (f) show the photovoltaic and voltammetric characterization of the material prepared using three different reaction times.
Chapter 5: The Use of Conducting Diamond in Electrochemistry
Figure 5.1 (a) Room temperature resistivity as a function of boron doping concentration. (Taken with permission from [14]). (b) p-type low-doped BDD at (i) absolute 0 K, no carriers are thermally excited from the valence band to acceptor states; the diamond is an insulator and the Fermi level,
E
F
, is mid-gap and (ii) nonzero temperature; the number of free carriers in the valence band will depend on the concentration and the ionization energy of the boron acceptors (
E
A
) and the temperature, yielding an activated electrical resistivity intermediate between that of an insulator and that of a metal; the Fermi level will move downward toward the top of the valence band. (iii) p-type heavily doped BDD (∼10
20
B atoms cm
−3
), when the impurities are close enough, quantum overlapping of their wave functions results in delocalization leading to metallic behavior at zero temperature with a Fermi level pinned inside the impurity band; the metal–insulator transition takes place. (iv) Very high doping levels >10
20
B atoms cm
−3
; screening of the impurities modifies the acceptor activation energy and the intrinsic band gap energy will reduce.
Figure 5.2 (a) Schematic showing grain structure of a thick polycrystalline diamond film. Differential boron uptake in different grains indicated by dark and light regions. (b) Processing of sample to remove growth and nucleation surfaces. (c) Resultant sample for investigation. Note the complex interconnection of grains with different dopant densities.
Figure 5.3 Different experimental arrangements used by researchers when working with BDD electrodes. (a) For thin-film BDD still attached to the growth substrate an glass electrochemical cell can be used. (Adapted from Ref. [35].) (i) Cu or Al metal current-collecting plate; (ii) the diamond film electrode; (iii) the Viton O-ring seal; (iv) the input for nitrogen purge gas; (v) carbon rod or Pt counterelectrode; and (vi) reference electrode. (b) Preparation of BDD free-standing electrodes. (Adapted from Ref. [36] with permission.) (i) Laser micro machining is used to cut the required BDD electrode geometry from a BDD free-standing wafer; (ii) here a cylinder is revealed. The electrode is ohmically contacted, sealed in glass, and polished flat to reveal the electrode structure in the left of (iii). Also shown are conventional polymer-sealed Pt, Au, and glassy carbon electrodes. (c) Scanning electron microscopy (SEM) images of a nanoelectrode array. (Adapted from Ref. [37].) (i) Overview of the design with distances of 10 µm between neighboring electrodes with hexagonal order (indicated in red) and (ii) recessed diamond electrode, the insulating diamond layer is clearly visible. (d) Schematic views of a top contacted BDD multiply addressable band electrode device, where the BDD band electrodes lie on insulating silicon oxide.
Figure 5.4 All-diamond coplanar micro- and macroelectrodes. (a) Multiple microelectrode array formed from machining pillar structures in free-standing BDD, overgrowing with insulating diamond, and then polishing flat to reveal a coplanar structure. SEM side on view of cross-sectioned microelectrode array. (Taken from Ref. [50] with permission.) (b) Atomic Force Microscopy (AFM) topography image of one of the electrodes in the array; the location of the BDD microdisk ultramicroelectrode is clearly visible. (Taken from Ref. [28] with permission.) (c) Top: multiple individually addressable microband array electrodes, of width 200 µm, formed by growing BDD into trench structures in insulating diamond. The NDC back contact to each electrode is visible. Bottom: top contacted BDD ring-disk electrode formed using the same procedure. The diameter of the disk electrode is 3 mm.
Figure 5.5 (a) SEM of an as-grown MC BDD electrode. (Taken from Ref. [62] with permission.); (b) Left: SEM of lapped surface of MC BDD; Right: corresponding Raman map of the same area. For both, zones of darker intensity correspond to more heavily boron-doped regions of the surface. (Taken from Ref. [18] with permission.) (c) SEM of thin-film BDD NC and (d) SEM of thin-film BDD UNC.
Figure 5.6 CVs recorded in 0.1 M KNO
3
at a scan rate of 0.1 V s
−1
for highly doped NDC-free free-standing, microcrystalline BDD (top), NDC-containing free-standing, microcrystalline BDD (second down), glassy carbon (third down), and platinum (bottom). The CVs have been plotted on different scales and vertically offset for clarity.
Figure 5.7 Cyclic voltammetric curves for a lower quality, NDC-containing thin film diamond film electrode in 0.1 M H
2
SO
4
before and after acid washing and rehydrogenation. Scan rate, 0.1 V s
−1
.
Figure 5.8 (a) Raman spectra of the [100] facet of B-doped individual diamond crystals recorded with a single-mode 514.5 nm line of an Ar-ion laser at low power (about 5 mW). “B/C” refers to B/C in the gas phase. (Taken from Ref. [73] with permission.) At low B, a NDC G peak is evident at ∼1500 cm
−1
; as the B concentration increases, the diamond phonon peak becomes more asymmetric and reduces in size. (b) Visible Raman spectrum for a boron-doped NC diamond thin film at laser wavelength = 532 nm and power = 50 mW. Integration time = 5 s.
Figure 5.9 (a) Schematic representation showing the position of the Ru(NH
3
)
6
3+
and FcTMA
+
couples with respect to valence (
E
VB
) and conduction (
E
CB
) bands for both O- and H-terminated semiconducting BDD. H-termination (O-termination) is known to induce a negative (positive) electron affinity, with a value of −1.3 eV (+1.7 eV) measured in vacuum [84]. The presence of water molecules screening the C−H (C−O) surface dipole is expected to reduce the value of the electron affinity (
χ
) toward less-negative (positive) values. We have chosen a value of approximately
χ
= −1.0 eV and
χ
= +1.3 eV for H- and O-terminated surfaces, respectively. In the electrolyte region, the level of the Ag/AgCl reference electrode (
E
ref
) is shown, and all applied voltages are referred to its energy. (b) CVs performed with a 1 mm diameter disk electrode of freestanding polished microcrystalline BDD electrode of dopant density (black line), (red line), mid-10
19
(blue line), (pink line), and (green line) at a scan rate of 0.1 V s
−1
for (i) the oxidation of 1 mM FcTMA
+
and (ii) the reduction of 1 mM Ru(NH
3
)
6
3+
in 0.1 M KNO
3
. (Taken from Ref. [17] with permission.) The resulting peak-to-peak (Δ
E
p
) separations are given for the differently doped electrodes in the two different redox mediator solutions.
Figure 5.10 Schematic illustration of (a) outer-sphere and (b) inner-sphere redox process. OHP is the outer Helmholtz plane and IHP is the inner Helmholtz plane.
Figure 5.11 (a) Schematic of the hydrogenated diamond surface in contact with a water layer as it forms in air. (b) Evolution of band bending during the electron transfer process at the interface between diamond and the water layer. VBM = valance band maximum, CBM = conduction band maximum,
E
F
= Fermi level,
μ
e
= chemical potential of the liquid phase.
Figure 5.12 (a) Contact angles for H- and O-terminated BDD [102] (b) XPS C1s spectra of semiconducting H-plasma-treated BDD (i) before and (ii) after electrochemical oxidation at 1.5 V for 10 min in 0.1 M KH
2
PO
4
[108].
Figure 5.13 CV curves. (a) H-terminated low-doped (∼10
18
) BDD electrode in 10 mM Fe(CN)
6
3−/4−
with 1 M KCl, scan rate = 25 mV s
−1
. (b) O-terminated low-doped (∼10
18
) BDD electrode in 10 mM Fe(CN)
6
3−/4−
with 1 M KCl, scan rate = 25 mV s
−1
. (c) O-terminated high-doped (∼10
20
) BDD electrode in 3 mM Fe(CN)
6
3−/4−
with 1 M KCl, scan rate = 20 mV s
−1
.
Figure 5.14 (a) Schematic illustrating SECM SG-TC mode. The heterogeneously active BDD electrode is biased at a potential to electrolyze the redox couple (Ox to Red or Red to Ox). The tip is biased at a suitable potential to convert the electro-generated species back to its original form at a diffusion-controlled rate. Variations in tip current reflect variations in the underlying ET capabilities of the surface. In feedback, the tip is biased to electrolyze the redox couple and the substrate left unbiased or biased to turn over the electro-generated form of the redox couple at a diffusion limited rate. (b) SECM SG-TC image of polished free-standing MC BDD, , for substrate generation of Ru(NH
3
)
6
2+
from Ru (NH
3
)
6
3+
at a 25-µm-diameter imaging tip. (Taken from Ref. [28] with permission.) (c) SECM feedback image of polished free-standing MC BDD, , recorded with a 2 µm tip electrode biased at a potential to convert Ru(NH
3
)
6
3+
to Ru(NH
3
)
6
2+
. (Taken with permission from Ref. [121].) (d) Scanning Raman image (left) and intermittent contact SG-TC SECM image (right) of the surface of polished free-standing MC BDD, , with a 2 µm tip electrode, biased at a potential to convert FcTMA
2+
to FcTMA
+
.
Figure 5.15 (a) Boron-doped film with its HPHT substrate before cutting and polishing. (b) Freestanding boron-doped diamond film.
Figure 5.16 SEM and AFM images of different metal NPs deposited under different conditions on BDD. (a) SEM images of flower-like (left) and spherical gold NPs electrodeposited on MC BDD by varying the electrodeposition conditions. (Taken from Ref. [143] with permission.) (b) SEM of citrate-capped gold NPs formed on as-grown BDD by the layer-by-layer assembly procedure. (Taken from Ref. [154] with permission.) (c) SEM of platinum nanoparticles electrodeposited on BDD microelectrodes after two deposition cycles. (Taken from Ref. [149] with permission.) (d) AFM image of nickel hydroxide nanoparticles deposited on free-standing polished MC BDD by electrochemically generating OH
−
in the presence of Ni
2+
.
Figure 5.17 CV responses of 0.1 M phosphate buffer solution pH4 at a scan rate of 50 mV s
−1
in the absence and presence of 1 mM arsenic(III) at (a) BDD electrode, (b) Ir-wire electrode, and (c) Ir-BDD electrode.
Figure 5.18 (a) Description of the successive diamond surface functionalization steps: first, amination with rf plasma, then aminolysis with 4-pentynoic acid, yne coupling using a thiolated oligonucleotide. (Modified from Ref. [180] with permission.) (b) Illustration of the multistep functionalization of BDD electrodes: first, diazotization, then electroreduction of the diazonium salt for electrografting of phenylazide molecules and finally click cycloaddition between the immobilized phenylazide molecules and ss-DNA (fluorescently labeled).
Chapter 6: Modification of Carbon Electrode Surface
Scheme 6.1 Reductive electrografting of aryldiazonium on a carbon surface.
Figure 6.1 Cyclic voltammograms recorded at a GC electrode without DPPH (left) and with 1 mM of DPPH (right) in a solution of CH
3
CN containing 0.1 M tetrabutylammonium hexafluorophosphate and 1 mM of 4-nitrobenzenediazonium at a scan rate of 50 mV s
−1
.
Figure 6.2 Mass versus time response of a carbon coated quartz crystal microbalance for the electrochemical grafting of 4-nitrobenzenediazonium (1 mM) at a fixed potential of −0.5 V versus Ag/AgNO
3
. Data are fitted using the Langmuir model (solid lines).
Scheme 6.2 Reaction to attach silyl groups at the para position of aryldiazonium.
Scheme 6.3 Modification process to get monolayer surface coverage on carbon using different protecting groups.
TMS
,
TES
,
TIPS
, and TBAF represent trimethylsilyl, triethylsilyl, tri(isopropyl)silyl, and tetrabutylammonium fluoride, respectively.
Figure 6.3 Comparison of bias stability of molecular junctions with Cu and e-C as top contacts. Cu junction breaks down at approximately −1.86 V, due to electrochemical oxidation of Cu, while e-C is stable up to a bias of 3.5 V.
Scheme 6.4 Oxidative electrografting of amine on carbon surface.
Figure 6.4 CVs obtained at GC in a solution of ethanol containing 0.1 M LiClO
4
and 1 mM (a) butylamine, (b)
N
-methylbutylamine, (c)
N
-ethylbutylamine, (d)
N,N
-dimethylbutylamine, and (e) triethylamine. The scan rate was 10 mV s
−1
.
Figure 6.5 XPS spectra in the N(1 s) region for GC electrode modified by cycling the potential once between 0.0 and 1.4 V versus Ag/AgCl in ethanolic solutions of 1 mM (a) butylamine, (b)
N
-methylbutylamine, (c)
N
-ethylbutylamine, and (d)
N,N
-dimethylbutylamine. Scan rate was 10 mV s
−1
Figure 6.6 CVs measured at GC (a,c) and pyrolyzed photoresist films (b,d). (a,b) First scan (—) and second scan (- - -) (0.2 V s
−1
) with stirring between scans in a solution of 5.2 mM 1-naphthylmethylcarboxylate and 0.1 M tetrabutylammonium tetrafluoroborate in acetonitrile. (c,d) Scans of 3.1 mM in aqueous 0.2 M KCl at bare (- - -) and 1-naphthylmethylcarboxylate modified (—) surfaces.
Scheme 6.5 Mechanism of grafting by using a redox mediator.
Scheme 6.6 Oxidative electrografting of alcohol on carbon surface.
Scheme 6.7 Various surface construction strategies on iodinated PPF. Firstly, PPF surface is iodinated by exposing it to iodine plasma. Iodinated surface can then be reacted with different alkene and alkyne compounds in the presence of appropriate light (A, B, and C). Further surface modification can then be achieved via “click” reaction (B) or attachment of nanoparticle (C).
Scheme 6.8 Modification of graphene with (a) monoaryldiazonium salt, (b) biaryldiazonium salt, and (c) bipyrene-terminated molecular wire.
Scheme 6.9 Reversible interaction of charged pyrene derivatives on graphite surface.
Scheme 6.10 Water contact angle (a) and water absorption (b) images of untreated and CTAB-treated carbon felts.
Scheme 6.11 Electrodeposition of MWCNTs using CTAB surfactant. (a), (b) and (c) show the possible arrangements of CTAB on MWCNTs.
Chapter 7: Carbon Materials in Low–Temperature Polymer Electrolyte Membrane Fuel Cells
Figure 7.1 Schematic illustration to categorize the most prominent carbon materials.
Figure 7.2 The three characteristics of carbon black determining its rich properties: particle size, aggregate structure, and surface chemistry.
Figure 7.3 Templating strategy for obtaining CMK-3 carbon from SBA-15 silica [10].
Figure 7.4 Images of the most prominent carbonaceous support materials: (a) graphite and (b) Vulcan carbon. (Taken from Ref. [14]. Copyright (2014), with permission from Elsevier Limited).
Figure 7.5 Comparison of Raman spectra of different carbon materials [16].
Figure 7.6 C K-edge NEXAFS spectra of different carbon materials (J. Melke, unpublished results).
Figure 7.7 Schematic illustration of the three-phase boundary in fuel cell electrodes.
Figure 7.8 False-color image of an ultrathin section of a fuel cell electrode; the inset shows a typical carbon agglomerate.
Figure 7.9 (a) Current–voltage characteristics of the three morphologically different support materials with the long fibers displaying the highest power output. (b) The chord length distributions for the long and short fibers are compared.
Figure 7.10 Comparison of 3D-reconstructed volumes of (a) an airbrushed electrode and (b) an LbL-prepared electrode (b). [131] (
Figure 7.11 Electron micrographs of a cross section of a multilayer electrode composed of bilayers of Pt on Sb-doped tin oxide and multiwalled carbon nanotubes in different magnifications [147].
Figure 7.12 Electrospun and carbonized PAN fibers decorated with Pt (a; bright spots attributed to Pt particles) and an overview of the final freestanding porous electrode structure (b).
Figure 7.13 (a) Schematic illustration of a Pickering emulsion and (b) SEM picture of the respective Pt/SnO
2
shell around a polyaniline (PANI) core sample.
Figure 7.14 (a) Cross section through a catalytic layer formed by “self-assembly” of the Pickering emulsion and (b) the corresponding fuel cell polarization curve.
Chapter 8: Electrochemical Capacitors Based on Carbon Electrodes in Aqueous Electrolytes
Figure 8.1 Schematic representation of the charged state of a symmetric electrical double-layer capacitor using porous electrodes and its simplified equivalent circuit.
Figure 8.2 Ragone plot of various electrochemical energy storage systems.
Figure 8.3 Gravimetric capacitance versus (a) BET and (b) DFT specific surface area.
Figure 8.4 Molar proportions of TEA
+
and BF
4
−
calculated from the NMR spectra, and relative amount of AN versus the total amount of electrolyte species, after polarization at various cell potentials for 30 min in the (a) positive and (b) negative electrodes of AC/AC electrochemical capacitor.
Figure 8.5 Volumetric capacitance of microporous carbons in TEABF
4
/AN electrolyte
vs
average width (
L
o
) of pores accessible to CCl
4
[57].
Figure 8.6 Nitrogen adsorption/desorption isotherms obtained at 77 K (a) and quenched solid density functional theory (QSDFT) pore size distribution (b) of AC, AC-PTFE, and AC-PVDF electrodes. For the electrodes, the amount of nitrogen adsorbed is referred to the mass of AC [60].
Figure 8.7 Ragone plots of AC/AC capacitors in 1 mol l
−1
Li
2
SO
4
and 6 mol l
−1
KOH aqueous solutions with cell operating potential windows 0–1.6 and 0–1.0 V, respectively. Values calculated for the total mass of active materials.
Figure 8.8 Three-electrode cyclic voltammograms (2 mV s
−1
) showing the potential stability window of AC in 6 mol l
−1
KOH, 1 mol l
−1
H
2
SO
4
, and 0.5 mol l
−1
Na
2
SO
4
[17].
Figure 8.9 Three-electrode cyclic voltammograms of AC in 2 mol l
−1
Li
2
SO
4
. The various loops are obtained by stepwise shifting of the negative potential limit. The vertical dashed line at −0.35 V versus NHE corresponds to the thermodynamic potential for water reduction.
Figure 8.10 Variation of pH value after cathodic charging (−500 mA g
−1
for 12 h) of AC electrodes in 0.5 mol l
−1
Na
2
SO
4
solutions where the initial pH was adjusted by addition of 1 mol l
−1
H
2
SO
4
or 1 mol l
−1
NaOH.
Figure 8.11 Scheme of the accelerated aging protocol (a) and magnification of the fifth galvanostatic cycle (b). The fifth discharge cycle of each series is considered to estimate the capacitance and ESR values.
Figure 8.12 Effect of floating cell potential at 24 °C on the (a) relative capacitance and (b) relative resistance of an AC/AC capacitor in 1 mol l
−1
Li
2
SO
4
[98].
Figure 8.13 Pore size distribution (PSD) of a fresh electrode (full dark gray line) and of aged positive (dashed light grey line) and negative (dotted light grey line) electrodes after 120 h of floating at 1.7 V in 1 mol l
−1
Li
2
SO
4
. The Quenched Solid Density Functional Theory (QSDFT) was used to determine the PSD [98].
Figure 8.14 TPD on pristine ACC (full dark grey line) and on aged positive (dashed light grey line) and negative (dotted light grey line) carbon electrodes after 120 h of floating at 1.7 V in 1 mol l
−1
Li
2
SO
4
: (a) mass loss and CO
2
evolution; (b) mass loss and CO evolution; (c) deconvolution of CO
2
; and (d) CO patterns (full light grey line: TPD experimental data; dashed lines: individual peaks; thick dashed line: sum of the individual peaks).
Figure 8.15 Nyquist plots of AC/AC capacitors at 0 V before and after floating at 1.6 V for 120 h in (a) 1 mol l
−1
Li
2
SO
4
and (b) 1 mol l
−1
Li
2
SO
4
+ 0.1 mol l
−1
Na
2
MoO
4
[106].
Figure 8.16 Voltammetry characteristics of an AC/AC cell in 1 mol l
−
1
KI solution: (a) AC/AC cell with SCE reference at 5 mV s
−
1
; (b) two-electrode system at 1, 10, and 100 mV s
−
1
potential scan rate.
Figure 8.17 Cyclic voltammograms (at 1 mV s
−1
) of two-electrode cells operating with activated carbons AAC 1 or AAC 2 in iodide/vanadium conjugated redox couples as electrolyte solutions [112].
Chapter 10: Carbon Electrodes in Molecular Electronics
Figure 10.1 Generalized schematic of a generic molecular junction, consisting of a molecule (can be one or many) placed between two conductors (examples for each contact are for illustrative purposes). As shown, a wide variety of materials can be used, and the choice of molecules and contacts can impact the specific electronic interactions at the interface – chemisorption (C−C, Si−SiOx) or physisorption (π–π, S−Au, etc.), which can exert a controlling influence on junction behavior. Upon application of voltage across the junction, current flows across the molecular layer. However, the system should be treated as whole, as the thickness and electronic properties of the molecule are not the only factors that will dictate conductivity.
Figure 10.2 Scheme showing chemically modified electrodes that are used to study various electrochemical processes, including electron transfer rates across molecules.
Figure 10.3 Various structures of molecular junctions commonly used in molecular electronics: (a) Cross junction formed by perpendicularly oriented bottom and top contacts with a molecular layer sandwiched between the conductors. Typical junction sizes range from several square microns to a square millimeter. (b) An all-carbon molecular junction formed using pyrolyzed photoresist film (PPF) (on SiO
2
support) as a bottom contact, an evaporated carbon (eC) top contact, and a molecular layer consisting of a multilayer of biphenyl grafted using diazonium chemistry. (c) Molecular junction made by contacting a thiols-based self-assembled molecular layer on Ag with a liquid–metal (in this case, a eutectic alloy of Ga and In). ((c) Reproduced from Ref. [36].) (d) A mechanically controlled break junction formed using
retractable
electrodes controlled with an STM, where molecules in solution bridge the gap to result in a junction [37]. (e) Other experimental geometries for studying electronic properties of single carbon nanotubes or a graphene nanoribbon can be made through forming contacts with lithographic methods.
Figure 10.4 Fabrication and measurements of molecular junction formed on PPF using diazonium chemistry. (a) Cyclic voltammogram measured at a PPF electrode featuring an irreversible reduction peak at approximately −0.8 V that corresponds to the reduction of diazonium ions with subsequent formation of a C−C with PPF. Growth of the molecular layer results in the increased blocking of electron transfer from the electrode and gradual decrease of the peak intensity (see also Chapter 6 on carbon electrode modification). (b) AFM image of the molecular layer obtained in (a), showing that film is homogeneous, and that the thickness can be measured using AFM. (c) Overlay of the current density–voltage characteristics (semilogarithmic scale) of eight junctions showing good reproducibility. (d) Raman spectra (measured with a 514 nm probe through an optically transparent quartz/PPF substrate made by diluting the photoresist) of a Q/PPF/NAB/Cu junction with and without a Cu top contact showing no changes in the structure of a nitroazobenzene molecular layer. (c) (Reprinted with permission from Ref. [72]. Copyright (2010) American Chemical Society). (d)
Figure 10.5 Bias and temperature stability of all-carbon MJs: (a) Comparison of Cu and e-C as top contacts, showing that the use of Cu leads to breakdown at approximately −1.86 V (due to electrochemical reactions of Cu), while e-C shows stability to ±3.5 V (with current densities up to ∼1500 A cm
−2
), junction area: ). (b) Overlay of
J–V
curves for PPF/NAB(4.1)/Au and PPF/NAB(4.1)/eC(10)/Au junctions showing that 10 nm of e-C prevents penetration of Au. (c)
J–V
curves of PPF/NAB(4.5)/e-C junction after heating in vacuum for 30 min at each temperature. (d)
J–V
curves of a PPF/NAB(4.5)/e-C junction before and after cycles at 100 °C in lab ambient (air) over the course of ∼68 h. (Adapted with permission from Ref. [82].) (e)
J–V
curves of a PPF/BrP(3)/e-C/Au junction before and after the application of ±0.8 V DC bias for 1–4 h at room temperature. Insets display the same data plotted in a semilog scale.
Figure 10.6 (a,b) Electronic band structure of graphene showing valence and conduction bands touching at the Dirac points and having a linear dispersion relation around the Fermi level. Comparison of (c) zero-band gap graphene, (e) band gap-opened graphene, and (d) a semiconductor, suggesting the possible use of zero-band gap graphene as a conductor for MJs and with a band gap as a molecular layer.
Figure 10.7 Reversible switching of conductance in a junction consisting of graphene functionalized with spiropyran. Spiropyran, a photochromic switch attached to G noncovalently, is able to change states between the ring closed (small dipole moment) and ring open (larger dipole moment) upon irradiation with UV and visible light. (a) Changes in the electronic configuration of spiropyran are translated into changes of the position of Dirac point of graphene (b), resulting in changes in the applied gate voltage (c) and conductance (d).
Figure 10.8 Graphene functioning as top and bottom electrodes for MJs. (a) Similarly to eC, the presence of graphene between molecular layer and Au top contact protects the junction from short circuits between electrodes. (Reproduced from Ref. [106].) (b) Using diazonium chemistry, an azobenzene layer was grown covalently on a graphene bottom contact, while a top graphene electrode was contacted physically. The mechanical and optical properties of graphene electrodes allowed testing of electronic properties under mechanical stress, and (c) photochemical switching of azobenzene between cis- and trans-isomers induced by multicycle switching (d) of the conductance of the junction, which was reversible (e).
Figure 10.9 Formation of a carbon nanotube by rolling up a graphene sheet. Depending on the chiral vector along which the nanotube is rolled, zigzag, armchair, and other chiral options are possible resulting in metallic or semiconducting CNTs.
Figure 10.10 Construction of FETs with individual (a and b) and collective (c) nanotubes. (a) AFM image of an FET composed of gold source and drain electrodes and an individual carbon nanotube as a channel. A heavily doped wafer served as a back gate electrode. Alternatively, an individual top gate electrode made of Ti can be employed (b). (a,b) (Reprinted with permission from Ref. [132], Copyright (2002) American Chemical Society.) (c) FET composed of an array of CNTs, with an individual gate Ti/Au electrode, separated with an Al
2
O
3
/SiO
2
insulating layer and Ti/Pd source and drain electrodes.
Figure 10.11 (a) A gap in a nanotube is created using an oxygen plasma to yield a space of few nanometers, which is suitable for the formation of a molecular junction. The ends of carbon nanotubes terminated with carboxylic groups and serving as a point of contact for further functionalization. (b) Oligoaniline placed between CNT contacts allows (c) reversible switching of the conductance in the junction by changes in the pH due to protonation/deprotonation.
Figure 10.12 A generic energy level diagram of a molecular junction showing the Fermi level of the contacts offset from molecular HOMO and LUMO levels to define interfacial barriers (here, a barrier to hole transport mediated by the HOMO is shown, (
φ
)). Filled states in the conductors are shaded. A parallel situation can be drawn for electron tunneling (using the LUMO).
Figure 10.13 (a) Attenuation plot for an electrochemical experiment shown in (c). Here, the lln of the electrochemical rate constant is plotted against thickness to yield a slope of 0.22 Å
−1
(or 2.2 nm
−1
). (b) Attention plot for a series of aromatic molecules and an aliphatic species by molecular junctions of different thickness of each (a corresponding diagram of the molecular junction is illustrated in (d)). See original text for structures and abbreviations. Here, the aromatic molecules give similar behavior due to the interactions between the molecular layers and the substrate, as discussed in the text. (a) (Reprinted with permission from Ref. [166]. Copyright (1999) American Chemical Society.) (b), (d)
Chapter 11: Carbon Paste Electrodes
Figure 11.1 Typical microstructures of two related graphite powders and four different carbon paste mixtures made of these carbons. Abbreviations and symbols used: C
spe
, spectroscopic (or spectral) graphite; C
nat
, refined natural graphite; SO, silicone oil; TCP, tricresyl phosphate; and IL, ionic liquid (BMImPF6); the individual carbon pastes denoted accordingly above the respective images (a–f). Experimental conditions: scanning electron microscopy, magnification: 1 : 1000 (a–e); scale: the actual size of photos corresponds really to (25 µm × 35 µm), 1 : 500 (f;
s
= 50 µm). Hitherto unpublished photos from authors' archives, except “(e)” being the alternate view of an image published in [37]. For other specification and details, see [35, 37, 58, 60].
Figure 11.2 Typical microstructures of two new forms of carbon and four carbon paste mixtures, made of traditional oil binders and ionic liquid. Abbreviations and symbols used: C
spe
, spectroscopic graphite powder; GC, glassy carbon powder (“Sigradur®”); CNTs, carbon nanotubes (“SW-” type); MO, mineral oil; SO, silicone oil (highly viscous type); and IL, ionic liquid (BMImPF6); the individual carbon paste mixtures denoted accordingly above the respective images (a–f). Experimental conditions: scanning electron microscopy, magnification: 1 : 1000, scale as in Figure 11.1. Hitherto unpublished photos from authors' archives, except “(a)” being the alternate view of an image published in [37]. For other specification and details, see [35, 37, 58–60].
Figure 11.3 Typical features and behavior of traditional or new carbon pastes and the respective electrodes in current flow measurements. (a–d) Cyclic voltammetry of [Fe(CN)
6
]
3/4−
in 0.1 M KCl, c(Fe) = 5 mM, lighter line, GCE (a,b) or GC-IL (c,d), hitherto unpublished records; (e) Adsorptive stripping voltammetry of Ni
II
at the low parts per billion level in 0.1 M ammonia buffer containing 10 μM DMG (dimethyl glyoxime) + Hg
II
. Legend: curve (1) blank, (2) c(Ni
II
) = 5 ppb, and (3) c(Ni
II
) = 10 ppb. Note: symbol O
2
denotes the reductive response of oxygen entrapped in the paste; an outtake from [84]; (f) Cathodic reduction of iodine at higher concentrations accumulated in 0.1 M HCl via ion-pairing and extraction. Legend: curve (1) blank, (2) c(I
−
) = 0.01 mM, and (3) c(I
−
) = 0.1 mM; an outtake from [85]. Abbreviations and symbols used:
C
, spectral or natural graphite powder;
MO
, mineral oil;
SO
, silicone oil;
TCP
, tricresyl phosphate;
MF
-, mercury film;
CNTPE
, carbon nanotube paste electrode (“SW-CNTs/SO” type); and
CILE
, carbon ionic liquid electrode (“C
nat
/BMImPF6” type).
Figure 11.4 Three examples of typical applications of chemically (a–c) and biologically (d) modified carbon paste electrodes. (a,b) Calibrations of Pt
IV
and Ir
III
at the micromolar concentration level at a CPE modified “
in situ
” with quaternary ammonium salt. Legend: (a) baseline, (
2–5
) 1, 3, 6, and 9 μM Pt
IV
; (b)
(1
) baseline, (
2–5
) 3, 6, 9, and 12 μM Ir
III
experimental conditions: DPCSV; 0.1 M acetate buffer + 0.1 M KCl + 1 × 10
−5
M cetyl-tributylammonium bromide (CTAB, pH 4.5); accumulation potential and time: +0.9 V versus 30 s; stripping: from +0.9 to −0.3 V; scan rate and pulse height: 10 mV s
−1
; Δ
E
= −25 mV.
Chapter 12: Screen-Printed Carbon Electrodes
Figure 12.1 The screen printing process.
Figure 12.2 Mesh and mask geometry.
Figure 12.3 The basic elements of a multilayered electrode.
Figure 12.4 A scanning electron microscope image of a cross section of a screen-printed porous carbon electrode having a low IR drop.
Figure 12.5 The equivalent circuit of a porous carbon electrode. It consists of a single vertical ladder network in series with an
RC
parallel network. The ladder network models the response of pores in the body of the electrode, whereas the solitary
RC
parallel network models the response of the electrolyte solution. (In many cases, the capacitance of the electrolyte solution is better represented as a constant-phase element.)
List of Tables
Chapter 1: Properties of Carbon: An Overview
Table 1.1 Physical properties of HOPG at 300 K [47].
Chapter 2: Electrochemistry at Highly Oriented Pyrolytic Graphite (HOPG): Toward a New Perspective
Table 2.1 Summary of some key properties of different grades of HOPG
Chapter 3: Electrochemistry in One Dimension: Applications of Carbon Nanotubes
Table 3.1 Main covalent functionalization strategies for the modification of CNTs with general applications in electrochemistry
Table 3.2 Voltammetric parameters obtained from the cyclic voltammograms for 1.0 × 10
− 3
M AA
Table 3.3 Noncovalent functionalization of CNTs: comparison of different types of dispersing agents and their general applications in electrochemistry
Chapter 5: The Use of Conducting Diamond in Electrochemistry
Table 5.1 Physical properties of diamond [11, 12].
Table 5.2 List of commercial companies selling BDD electrodes.
Table 5.3 Nonexhaustive Table of Δ
E
p
values recorded for simple redox species by different authors using differently prepared BDD electrodes.
Table 5.4 Nonexhaustive list of different metal NPs deposited on BDD electrodes for the electrocatalytic detection of a range of different analytes.
Chapter 7: Carbon Materials in Low–Temperature Polymer Electrolyte Membrane Fuel Cells
Table 7.1 Overview of characterization methods applied to unravel the geometric and electronic structures of different carbons
Table 7.2 Overview of various Raman bands and their interpretation
Table 7.3 List of requirements which a good support material has to fulfill and exemplary data for VulcanXC-72
Table 7.4 Overview of prominent carbon black materials applied in fuel cell research
Chapter 9: Carbon Electrodes in Electrochemical Technology
Table 9.1 Typical conditions for the manufacture of metals by molten salt electrolysis
Table 9.2 Current efficiency for the formation of ozone as a function of HBF
4
concentration for cells with glassy carbon anodes and air GDE cathodes
Table 9.3 The electro-generation of strong oxidants at boron-doped, diamond-coated anodes
Chapter 10: Carbon Electrodes in Molecular Electronics
Table 10.1 Thickness, voltage, and temperature dependence for various charge transport mechanisms relevant in molecular electronics
Chapter 11: Carbon Paste Electrodes
Table 11.1 Survey of (unmodified) carbon pastes and the corresponding carbon paste electrodes
Table 11.2 Common modifiers for carbon paste electrodes with typical examples.
Table 11.3 Modifying agents for carbon paste biosensors with typical examples.
Chapter 12: Screen-Printed Carbon Electrodes
Table 12.1 Halogen-free, high-boiling solvents for PVDF
