Graphite intercalation in H2SO4-CH3COOH electrolytes

Article abstract of DOI:10.1023/A:1025021212474

The anodic oxidation of highly oriented pyrolytic graphite in H ₂SO₄-CH₃COOH electrolytes in a galvanostatic mode (I = 1.5 mA) is studied as a function of electrolyte composition. The concentration ranges for the formation of stage I-V graphite intercalation compounds (GICs) are determined. The concentration threshold for intercalation is ～1 wt % H₂SO₄. There are three distinct concentration ranges differing in the shape of the charging curve E(Q), which depends primarily on the content of H₂SO₄ (active intercalant). The potentials of formation of stage I-III GICs in H ₂SO₄-CH₃COOH electrolytes are found to be higher than those for graphite bisulfate, which points to an increase in the potential barrier for intercalation and is obviously associated with the intercalation of acetic acid into the graphite host. The specifics of the charging curves obtained in 60-80% H₂SO₄, together with gravimetry and chemical analysis data, indicate the formation of ternary GICs with sulfuric and acetic acids. In this composition range, stage I* and II* cointercalation compounds are obtained, with an intercalate layer thickness d_i, = 7.94 A. The composition of the ternary GICs is shown to depend on the relative amounts of the acids in the electrolyte. A mechanism of the formation of graphite cointercalation compounds is proposed. In solutions containing less than 40 wt % H₂SO₄, only graphite bisulfate is formed.

Full text of DOI:10.1023/A:1025021212474

Inorganic Materials, Vol. 39, No. 8, 2003, pp. 826–832. Translated from Neorganicheskie Materialy, Vol. 39, No. 8, 2003, pp. 964–970.
Original Russian Text Copyright © 2003 by Leshin, Sorokina, Avdeev.
Graphite Intercalation
in H2SO4–CH3COOH Electrolytes
V. S. Leshin, N. E. Sorokina, and V. V. Avdeev
Moscow State University, Moscow, 119899 Russia
e-mail: Nsorokina@mail.ru
Received February 18, 2003
Abstract—The anodic oxidation of highly oriented pyrolytic graphite in H2SO4–CH3COOH electrolytes in a
galvanostatic mode (I = 1.5 mA) is studied as a function of electrolyte composition. The concentration ranges
for the formation of stage I–V graphite intercalation compounds (GICs) are determined. The concentration
threshold for intercalation is ~1 wt % H2SO4. There are three distinct concentration ranges differing in the shape
of the charging curve E(Q), which depends primarily on the content of H2SO4 (active intercalant). The poten-
tials of formation of stage I–III GICs in H2SO4–CH3COOH electrolytes are found to be higher than those for
graphite bisulfate, which points to an increase in the potential barrier for intercalation and is obviously associ-
ated with the intercalation of acetic acid into the graphite host. The specifics of the charging curves obtained in
60–80% H2SO4, together with gravimetry and chemical analysis data, indicate the formation of ternary GICs
with sulfuric and acetic acids. In this composition range, stage I* and II* cointercalation compounds are
obtained, with an intercalate layer thickness di = 7.94 Å. The composition of the ternary GICs is shown to
depend on the relative amounts of the acids in the electrolyte. A mechanism of the formation of graphite coint-
ercalation compounds is proposed. In solutions containing less than 40 wt % H2SO4, only graphite bisulfate is
formed.
INTRODUCTION
dation of graphite in solutions of different acids. In
most studies dealing with the synthesis of ternary GICs
in a galvanostatic mode, electrochemical oxidation was
carried out at high currents. This approach was used
with success to synthesize ternary GICs in the systems
graphite–H2SO4–HNO3 [1], graphite–H2SO4–H2SeO4
[2], graphite–H2SO4–CH3COOH [3], and graphite–
H2SO4–HCOOH [6]. It can be seen that the intercalants
used in those studies were either strong Brönsted acids
or organic acids. Earlier work has shown that, in the
synthesis of ternary GICs, the composition, structure,
and properties of both the resultant intercalation com-
pounds and the products of further processing (oxi-
dized graphite and cellular graphite) can be closely
controlled. For example, Kang et al. [3] reported the
preparation of oxidized graphite with a low content of
sulfur (corrosive agent) from ternary GICs with H2SO4
Recently, a great deal of attention has been paid to
ternary graphite intercalation compounds (GICs), con-
taining two intercalate species. Most of the research
effort has been concentrated on donor compounds.
There has been much less work on acceptor compounds
with a strong Brönsted acid and another mineral or
organic acid. The possibility of preparing such GICs
was examined in only a few studies [1–3].
Binary GICs with strong acids, in particular graphite
bisulfate, are not only important model substances for
gaining insight into the chemistry and physics of two-
dimensional systems but also precursors for the prepa-
ration of new valuable carbon materials, such as oxi-
dized graphite and cellular graphite. Graphite bisulfate
is commonly prepared either by reacting graphite with
H2SO4 in the presence of strong oxidants (K2Cr2O7,
CrO3, (NH4)2S2O8, and others) or via anodic oxidation
of graphite in an H2SO4 solution [4, 5]. In fundamental
studies, the latter approach is preferable because it pro-
vides more information, requires no additional oxi-
dants, and offers the possibility of close control over the
synthesis conditions.
and CH3COOH with the general formula C+m HSO4– ·
xH2SO4 · yCH3COOH (x and y were not specified).
They studied the anodic oxidation of natural graphite in
H2SO4–CH3COOH electrolytes containing 20–80 vol %
H2SO4 (32–88 wt %) and found that the shape of the
E(τ) curve was determined by the solution composi-
tion. With decreasing H2SO4 content, the steplike char-
acter of the charging curve became less pronounced: in
electrolytes containing less than 50% H2SO4, no pla-
The methods used to prepare binary GICs with acids
could be adapted for the synthesis of ternary GICs.
Analysis of published data suggests that the most prom-
ising approaches are electrochemical graphite interca- teaus or steps were seen in the charging curve. The
lation in a mixture of acids or consecutive anodic oxi-
intercalation threshold was 3.65 M H2SO4 (20 wt %).
0020-1685/03/3908-0826$25.00 © 2003 MAIK “Nauka/Interperiodica”

GRAPHITE INTERCALATION IN H2SO4–CH3COOH ELECTROLYTES
827
Ioveroxidized
The average thickness of the intercalate layer was di =
2.0
1.5
1.0
0.5
I + “overoxidation”
7.77 Å in all of the GICs prepared in that work. Kang
et al. [3] believe that the cointercalated acetic acid has
a smaller effective diameter than H2SO4, which reduces
the separation between the graphite layers.
I
III
II + I
II
+
II
III
In this paper, we report the first systematic study of
the electrochemical behavior of highly oriented pyro-
lytic graphite in concentrated H2SO4 and H2SO4–
CH3COOH electrolytes containing 1 to 100 wt %
H2SO4 (active intercalant).
0
100 200 300 400 500 600 700
Q, C/g
Fig. 1. Charging curve in the graphite–H SO system.
2
4
EXPERIMENTAL
As starting reagents, we used UPV-1-TMO highly
oriented pyrolytic graphite (interlayer spacing of
3.354–3.359 Å) and reagent-grade H2SO4 (ρ =
1.84 g/cm3) and glacial CH3COOH (ρ = 1.05 g/cm3).
Solutions with intermediate concentrations (1–80 wt %
H2SO4) were prepared by mixing appropriate ratios of
the acids.
cointercalation compound was found as the difference
between the weight gain and the weight of the interca-
lated H2SO4.
RESULTS AND DISCUSSION
Graphite–H2SO4 system. To enable comparison
with the graphite–H2SO4–CH3COOH system, the
binary and ternary systems were studied at identical
(high) electric currents. The results for the graphite–
H2SO4 system are presented in Table 1. The character-
istics of the graphite bisulfate agree with earlier data
[5]. The intercalate layer thickness is 7.94–7.96 Å,
independent of the oxidation state of graphite. The
charging curve of graphite in concentrated H2SO4
(Fig. 1) shows characteristic steps (corresponding to a
single-phase state) and plateaus (corresponding to mix-
tures of two consecutive stages). The potential of for-
Electrochemical intercalation was performed in a
galvanostatic mode (I = 0.5 mA). The dynamics of the
process were studied in a standard three-electrode cell.
The Pt working electrode with graphite (10-mg plate)
served as an anode. The potential was measured relative
to an Hg/Hg2SO4 reference electrode (E = 0.615 V ver-
sus a standard hydrogen electrode). The reaction prod-
ucts were characterized by x-ray diffraction (XRD)
analysis (DRON-2.0 powder diffractometer, CuKα radi-
ation), gravimetry, and chemical analysis.
The H2SO4 content of the resultant GICs was deter-
mined using an AS-7932 gas analyzer (sulfur determi-
nator). GIC samples were burnt at 1100°C in flowing
oxygen to decompose H2SO4. The resulting SO2 was
mation is EHg/Hg SO = 0.50–0.57 V for stage III, 0.60–
2
4
0.85 V for stage II, and 0.89–1.46 V for stage I GICs.
Note that the oxidation state of the graphite host
absorbed by an aqueous solution and oxidized to (Table 1) agrees well with earlier results [5]. Long-term
H2SO4, which was then titrated coulometrically. The oxidation after the formation of stage I graphite bisul-
fate revealed an interesting feature in the variation of
the sample potential with the quantity of electricity
passed, Q. The quantity of electricity needed to obtain
composition of the ternary GICs was inferred from
gravimetry data (0.5% accuracy) and sulfur determina-
tions (5% accuracy). The CH3COOH content of the
Table 1. Electrochemical synthesis of GICs in the graphite–H2SO4 system
Phase composition
C+p
∆m, %
wt % S
Composition
EHg/Hg SO , V
Q, C/g
2
4
(di, Å)
I (7.94)
I (7.96)
II (7.96)
III (7.96)
C+13
C+24
C+55
C+83
605
330
145
97
1.70
1.20
0.74
0.57
115
113
57
17.5
17.1
11.9
9.0
C7.1 · H2SO4
C7.2 · H2SO4
C14.3 · H2SO4
C21.5 · H2SO4
38
INORGANIC MATERIALS Vol. 39 No. 8 2003

828
LESHIN et al.
In electrolytes containing 60–80 wt % H2SO4, the
charging curves have a characteristic steplike shape:
with increasing Q, the potential rises stepwise, with a
Table 2. Synthesis of graphite cointercalation compounds
in a 60% solution of H2SO4 in acetic acid
Q, C/g
Stage (di, Å)
C+p
∆m, %
EHg/Hg SO , V
few plateaus, up to EHg/Hg SO = 1.8–1.9 V, correspond-
2
4
2
4
ing to the formation of a stage I* GIC. At intermediate
H2SO4 concentrations (20–40 wt %), the potential of
the graphite sample first rises monotonically and then
plateaus. Note that, the final reaction product in this
C+10
C+20
C+37
805
405
1.92
1.65
1.33
I* (7.94)
II* (7.94)
II (7.94)
85
70
55
concentration range is a stage II GIC with EHg/Hg SO Ӎ
215
2
4
1.5 V. According to XRD results, electrochemical oxi-
dation for 30 min yields a mixture of stage II and III
GICs in a 30 wt % H2SO4 solution and a mixture of
stage III and IV GICs in a 20 wt % H2SO4 solution.
These phase changes, however, have no effect on the
charging curve because the potential rises steeply at
small Q and rapidly exceeds the threshold for the for-
mation of GICs with large stage indices. For this rea-
son, the steps and plateaus corresponding to different
GICs are indiscernible.
* Ternary GIC.
stage I graphite bisulfate in the oxidation state C+21 is
1
Q = 380 C/g. An increase in Q from 400 to 600 C/g,
which corresponds to a change in the oxidation state to
C+13 , results in an extended plateau at EHg/Hg SO Ӎ 1.5 V.
2
4
Upon a further sample polarization, the potential
increases to EHg/Hg SO = 1.88 V.
2
4
The anodic oxidation of graphite in H2SO4–
CH3COOH solutions containing less than 20 wt %
H2SO4 was investigated for the first time. At low
(≤5 wt %) H2SO4 concentrations, the charging curves
Earlier, such an “overoxidation” plateau was only
observed by Metrot and Fischer [5], who studied the
behavior of graphite during further oxidation using an
equilibrium current of Ӎ10 µA. The origin of the over-
oxidation plateau can be understood in terms of side
processes, including the formation of chemical defects
(e.g., C–O bonds) at grain boundaries and the oxidation
of H2SO4 in the gaps between the layers of the graphite
host by the reaction
have an anomalous shape: a high potential (EHg/Hg SO
=
2
4
2–6 V) sets in at the very beginning of the process and
then gradually decreases, instead of rising. The reaction
yields a mixture of stage I–V GICs and graphite, rather
than two consecutive stages. Finally, the potential stops
varying, and the mixture transforms into one GIC, ener-
getically the most favorable.
C+24HSO4– xH2SO4 currentC+24
Several features of the anodic oxidation of graphite
in electrolytes containing 60–80 wt % H2SO4 were
revealed for the first time. Consider in detail the charg-
ing curve of graphite in a 60 wt % H2SO4 solution
(1)
1
2
2–
· S2O8 xH2SO4 + H+ + e–.
--
(Fig. 3). At EHg/Hg SO = 1.37 V, we obtain a stage II
According to gravimetry and chemical analysis
2
4
data, the general formula of the synthesized graphite GIC with a weight gain of 55%, which is intercalated,
bisulfate is C7.2n · H2SO4 (Table 1), where n is the stage
index. These results agree well with the reported com-
positions of graphite bisulfate, from C8n · H2SO4 [4] to
C6.8n · H2SO4 [5].
according to chemical analysis data, with H2SO4 only
(Tables 2, 3). Further sample polarization (Q > 300 C/g)
results in a plateau, followed by a rise in potential to
1.77 V, which corresponds to the formation of a
stage II* GIC with a weight gain of 70%. However,
analysis for sulfur points to a reduced H2SO4 content in
this GIC compared to the stage II graphite bisulfate,
which seems to be due to the incorporation of acetic
acid. As is known, acetic acid dissociates very little in
H2SO4 solutions, and it can be intercalated into graphite
together with H2SO4 via partial rearrangement of the
solvate shell of the bisulfate anion with the formation of
cointercalation layers. Chemical analysis for sulfur indi-
cates that, during further polarization of the stage II* ter-
nary GIC in a 60 wt % H2SO4 solution, only the strong
intercalant (H2SO4) is incorporated, leading to the for-
mation of a stage I* cointercalation compound at
Graphite–H2SO4–CH3COOH system. Our exper-
imental data on the galvanostatic oxidation of pyrolytic
graphite demonstrate that the concentration of the
active intercalant in the electrolyte has a profound
effect on the shape of the E(Q) curve. There are three
distinct concentration ranges differing in the behavior
of the graphite potential (Fig. 2).
+
1
The oxidation state of the graphite host, Cp , can be determined
using the well-known formula p = F/(AQ), where F = 96485 C/mol
is the Faraday constant, A = 12.011 g/mol is the molar mass of
carbon, and Q (C/g) is the quantity of electricity passed through
the sample per unit mass of carbon.
INORGANIC MATERIALS Vol. 39 No. 8 2003

GRAPHITE INTERCALATION IN H2SO4–CH3COOH ELECTROLYTES
829
2.5
2.0
1.5
1.0
0.5
(a)
100%
80%
200
400
600
800
1000
1200
0
(b)
1.6
1.4
1.2
1.0
0.8
40%
20%
0
200
400
600
(c)
800
1000
1200
7
6
5
4
3
2
1
5%
2%
0.8%
0%
0
1000
2000
3000
4000
5000
Q, C/g
Fig. 2. Charging curves of graphite in H SO –CH COOH electrolytes: (a) 100, 80, (b) 40, 20, (c) 5.2, 0.8, and 0 wt % H SO .
2
4
3
2
4
2.5
2.0
1.5
1.0
0.5
I
EHg/Hg SO = 2.05 V. In this process, the H2SO4 : graph-
2
4
II* + I*
II*
II + II*
ite ratio in the GIC rises to the value obtained in stage II
graphite bisulfate (0.55 : 1), and the CH3COOH :
graphite ratio remains constant at 0.30 : 1 (Table 3).
Table 3 also gives the overall compositions of the
stage II, II*, and I* GICs. The composition of the inter-
calate layer is seen to be close to that of the electrolyte
(H2SO4 : CH3COOH = 0.45 : 3).
II
0
200
400
600
800
1000
The formal oxidation states of graphite, C+p , listed in
Q, C/g
Table 2 were found under the assumption that the entire
Fig. 3. Charging curve of graphite in H SO –CH COOH
2
4
3
quantity of electricity Q went into graphite oxidation.
electrolyte containing 60 wt % H SO .
2
4
INORGANIC MATERIALS Vol. 39 No. 8 2003

830
LESHIN et al.
Table 3. Composition of graphite cointercalation compounds prepared in a 60% solution of H2SO4 in acetic acid
Graphite : H2SO4 : CH3COOH
Stage
∆m, %
wt % S
Composition
weight ratio
I*
II*
II
85
70
55
11.8
9.5
1 : 0.55 : 0.30
1 : 0.40 : 0.30
1 : 0.55 : 0
C7.8 · (H2SO4)0.52(CH3COOH)0.48
C9.0 · (H2SO4)0.45(CH3COOH)0.55
C14.6 · H2SO4
11.8
Table 4. Composition of GICs prepared in H2SO4 + CH3COOH electrolytes
Phase composition
wt %
EHg/Hg SO , V
Q, C/g
C+p
∆m, % wt % S
Composition
C7.2 · H2SO4
2
4
H2SO4
(Ic, Å)
C+24
C+12
C+10
C+19
C+17
100
80
60
40
20
330
675
805
420
470
1.20
1.80
1.92
1.48
1.53
I (7.96)
113
105
85
17.1
16.8
12.0
11.8
11.0
I* (7.94)
I* (7.94)
II (11.29)
II (11.30)
C7.3 · (H2SO4)0.85 · (CH3COOH)0.15
C7.8 · (H2SO4)0.52 · (CH3COOH)0.48
C14.6 · H2SO4
56
51
C16.0 · H2SO4
5
2
1
0
1100
>2000
>2000
>2000
1.53
2.40
3.30
II + III (11.30 + 14.65)
III (14.65)
–
–
–
–
46
42
10
0
–
–
–
–
–
–
–
–
IV + V + graphite
Graphite
>6
Note: At H SO contents of the electrolyte in the range 0–5 wt %, the composition of the GICs was not determined because of the high
2
4
defect density, amorphization, and high content of sorbed electrolyte.
The C+p of the stage II GIC corresponds then to the
stage II graphite bisulfate obtained in 96% H2SO4, the
range. Therefore, additional studies are needed to ver-
ify this result.
C+p of stage II* GIC corresponds to stage I graphite
bisulfate, and the oxidation state of the stage I* GIC
(C+10 ) has not been reported previously. Consequently,
In the solution containing 80 wt % H2SO4, we also
observe the formation of stage II* and stage I* GICs, at
EHg/Hg SO = 1.20 and 1.80 V, respectively (Fig. 2a).
2
4
However, the degree of CH3COOH substitution for
H2SO4 is here lower because, as shown above, it is
determined by the electrolyte composition.
during the anodic oxidation of graphite in the system
under consideration, some quantity of electricity goes
into unknown side processes. During the formation of
the cointercalation compounds, the thickness of the
intercalate layer remained constant at 7.94 Å, as in
graphite bisulfate. It is also of interest to note that the
overall compositions of the stage I* cointercalation
compound and stage II graphite bisulfate fall within the
standard range for graphite bisulfate: (7–8)n mol of car-
bon per mole of an acid (in our case, a mixture
of acids). At the same time, the composition of the
stage II* cointercalation compound (4.5n mol of C per
In the solutions containing 40 and 20 wt % H2SO4,
at EHg/Hg SO Ӎ 1.5 V we observe the formation of an
2
4
overoxidized stage II graphite bisulfate with a normal
composition, in which the oxidation state of the graph-
ite host is C+19–17 (Table 4). As seen in Fig. 2b, during
subsequent prolonged oxidation of graphite its poten-
tial does not exceed 1.55 V, which is obviously insuffi-
cient for overcoming the potential barrier for the forma-
mole of H2SO4 + CH3COOH) lies beyond the standard tion of a stage II* cointercalation compound, since this
INORGANIC MATERIALS Vol. 39 No. 8 2003

GRAPHITE INTERCALATION IN H2SO4–CH3COOH ELECTROLYTES
831
barrier is 1.65 V in a 60% solution of H2SO4 and must
rise with decreasing H2SO4 concentration.
7
6
5
4
3
2
Table 4 summarizes the results obtained by interca-
lating graphite in H2SO4–CH3COOH electrolytes. It
can be seen that GICs are formed over the entire range
of H2SO4 concentrations studied. With decreasing
H2SO4 content, the stage index increases. In solutions
containing more than 60 wt % H2SO4, stage I* GICs
are formed. At lower H2SO4 concentrations, we observe
the formation of stage II (20–40 wt %) and stage III (5–
10 wt %) compounds. GICs (large stage indices) are
formed even in glacial acetic acid containing 1 wt %
H2SO4. Thus, acetic acid extends the concentration
range of GIC formation and shifts the concentration
threshold for intercalation as compared to aqueous
H2SO4. Experiments with pyrolytic graphite allowed us
not only to understand the specifics of the intercalation
of two acids but also to notably extend the range of GIC
formation in solutions of H2SO4 in CH3COOH as com-
pared to the results obtained by Kang et al. [3] with nat-
ural graphite.
1
0
2
4
6
8
10 12 14 16 18
CH SO , mol/l
2
4
Fig. 4. Initial intercalation potential as a function of H SO
concentration in H SO –CH COOH electrolytes.
2
4
2
4
3
2.5
2.0
1.5
1.0
0.5
I
II
III
Increasing the CH3COOH content of the electrolyte
increases the quantity of electricity Q needed to obtain
a particular GIC. At high and intermediate H2SO4 con-
tents (80–20 wt %), Q exceeds the one needed for the
0
2
4
6
8
10 12 14 16 18
CH SO , mol/l
2
4
formation of graphite bisulfate (C+24 ) by a factor of 2–3;
Fig. 5. Potentials of formation of stage I–III GICs as func-
tions of H SO concentration in H SO –CH COOH elec-
trolytes.
2
4
2
4
3
in solutions containing less than 5 wt % GIC, Q rises by
tens of times. Our experimental data indicate that, with
increasing CH3COOH content, the energy that goes
into side processes (defect formation in the graphite
host and partial amorphization of the sample) rises
sharply, as evidenced by the marked reduction in the
intensity of the 00l reflections in the XRD patterns of
the samples.
The synthesized cointercalation compounds are
unstable and rapidly decompose even when stored in
the corresponding H2SO4–CH3COOH solutions. In this
process, the stage index increases from n to n + 1 within
24 h, independent of n, whereas graphite bisulfate per-
sists in concentrated H2SO4 solutions for several days:
over a period of 24 h, even the least stable stage I con-
verts to stage II only partially.
As the H2SO4 content of the electrolyte decreases
from 100 to 20 wt %, the initial intercalation potential
gradually decreases (Fig. 4). The slope dE0/dCH SO
=
2
4
–45 mV/M is steeper than that in the oxidation of pow-
dered natural graphite (–38 mV/M) [3]. At low H2SO4
concentrations (≤0.5 mol/l), where the charging curves
have an anomalous shape, the initial potential rises
steeply, and the concentration correction cannot be
evaluated accurately.
CONCLUSIONS
Intercalation compounds of highly oriented pyro-
lytic graphite were prepared by electrochemical oxida-
tion over the entire range of H2SO4–CH3COOH solu-
tions studied. The intercalation threshold is 1 wt %
H2SO4 in CH3COOH, which is far lower in comparison
with earlier results (20 wt % H2SO4) obtained with nat-
ural graphite [3]. The charging curves are found to have
an anomalous shape at low H2SO4 concentrations.
The potentials of formation of stage I–III GICs also
increase appreciably as H2SO4 is diluted with glacial
acetic acid (Fig. 5), which points to an increase in the
potential barrier for intercalation and is obviously asso-
ciated with both the reduction in solution acidity and
CH3COOH intercalation. The concentration correction
The anodic oxidation of graphite in H2SO4–
CH3COOH solutions containing 60–80 wt % H2SO4
leads to the formation of ternary GICs with acetic and
sulfuric acids, represented by an additional plateau in
the charging curve. The composition of the cointercala-
tion compounds, determined by combining gravimetry
dEf/dCH SO for the potentials of formation of stage III,
2
4
II, and I GICs in H2SO4–CH3COOH electrolytes is –58,
–58, and –73 mV/M, respectively.
INORGANIC MATERIALS Vol. 39 No. 8 2003

832
LESHIN et al.
3. Kang, F., Zhang, T.-Y., and Leng, Y., Electrochemical
Behavior of Graphite in Electrolyte of Sulfuric and Ace-
tic Acid, Carbon, 1997, vol. 35, no. 8, pp. 1167–1173.
and chemical analysis data, depends on the relative
amounts of the acids in the electrolyte. A mechanism is
proposed for the formation of graphite cointercalation
compounds.
4. Bottomley, M.J., Party, G.S., Ubbelohde, A.R., and
Young, D.A., Electrochemical Preparation of Salts
from Well-Oriented Graphite, J. Chem. Soc., 1963,
pp. 5674–5680.
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