Kinetic parameters of the electroreduction of oxygen on a graphitized carbon electrode activated by tetrakis(4-methoxyphenyl)porphyrin and its cobalt complexes

Article abstract of DOI:10.1134/S0036024411120326

Electrochemical and electrocatalytic properties of tetrakis(4- methoxyphenyl)porphyrin, tetrakis(4-methoxyphenyl)porphyrinatocobalt(II), and (tetrakis(4-methoxyphenyl)porphyrinato)chlorocobalt(III) are studied using the method of cyclic voltammetry. The redox-potentials of the electrode processes, the potentials of the half-wave and stationary rate constants for electroreduction of molecular oxygen are determined from an analysis of the voltammetric curves. The cobalt complex is found to be characterized by higher electrocatalytic activity than other analyzed compounds.

Full text of DOI:10.1134/S0036024411120326

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2012, Vol. 86, No. 1, pp. 9–13. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © M.V. Tesakova, A.V. Noskov, M.I. Bazanov, N.M. Berezina, V.I. Parfenyuk, 2012, published in Zhurnal Fizicheskoi Khimii, 2012, Vol. 86, No. 1, pp. 13–17.
CHEMICAL KINETICS
AND CATALYSIS
Kinetic Parameters of the Electroreduction of Oxygen
on a Graphitized Carbon Electrode Activated
by Tetrakis(4ꢀMethoxyphenyl)Porphyrin and Its Cobalt Complexes
a
a
b
b
a, b
M. V. Tesakova , A. V. Noskov , M. I. Bazanov , N. M. Berezina , and V. I. Parfenyuk
a
Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, 153045 Russia
b
Ivanovo State University of Chemistry and Technology, Ivanovo, 153000 Russia
eꢀmail: vip@iscꢀras.ru
Received December 21, 2010
Abstract—Electrochemical and electrocatalytic properties of tetrakis(
4ꢀmethoxyphenyl)porphyrin, tetꢀ
rakis( ꢀmethoxyphenyl)porphyrinatocobalt(II), and (tetrakis( ꢀmethoxyphenyl)porphyrinato)chlorocoꢀ
4
4
balt(III) are studied using the method of cyclic voltammetry. The redoxꢀpotentials of the electrode processes,
the potentials of the halfꢀwave and stationary rate constants for electroreduction of molecular oxygen are
determined from an analysis of the voltammetric curves. The cobalt complex is found to be characterized by
higher electrocatalytic activity than other analyzed compounds.
Keywords: macroheterocyclic compounds, electrocatalysis, electroreduction of oxygen, cyclic voltammetry,
halfꢀwave potential.
DOI: 10.1134/S0036024411120326
INTRODUCTION
ents in the paraposition of the phenyl rings of cobalt
porphyrins during the oxygen reduction. The main
electrochemical measurements were performed using
The reaction of electrochemical reduction of oxyꢀ
gen, which takes place in chemical power sources with
oxygen (air) depolarization, is accompanied by strong
polarization of the cathode, and quite active catalysts
are thus required for it to occur [1]. Platinum group
metals deposited on carbon supports are used as cataꢀ
lysts of electrode processes [2], but their high cost and
scarcity limit the possibilities for their wide applicaꢀ
tion. The search for new effective catalysts for the
reduction of molecular oxygen as an alternative of
noble metals is therefore of great importance [3].
a rotating disc electrode in 0.5 M solutions of H SO4.
2
Two pairs of maxima were found for tetrakis(4ꢀmethꢀ
oxyphenyl)porphyrinatocobalt(II); the first, at Ec
=
+/3+
0
.75 V, Еа = 0.9 V, was attributed to the Co2
transiꢀ
tion, while the weakly pronounced pair of maxima at
Ec = 0.3 V, Еа = 0.5 V was related to the same redoxꢀ
transition of Co2
+/3+
ions. The potential of the halfꢀ
wave of the О2 reduction process is 0.22 V. The authors
of [2] investigated the electrocatalytic activity of tetꢀ
rakis(4ꢀmethoxyphenyl)porphyrinatocobalt(II) using
a floating gasꢀdiffusion electrode and a rotating disc
electrode with ring in acidic and alkaline solutions.
The potentials of electron transitions were determined
in [5] for tetrakis(4ꢀmethoxyphenyl)porphyrin and its
complexes with Co(II) and Co(III) in dichloromethane
and DMSO.
One challenging line in the development of nonꢀ
platinum catalysts is the creation of carbonꢀbased
cathode materials modified by macroheterocyclic
compounds (porphyrins, phthalocyanines) and their
metallic complexes. According to [1], the catalytic
activity of metallic porphyrins in the electroreduction
of oxygen is related to their capacity for the reversible
coordination of oxygen. The extracoordination of
oxygen in metallic porphyrins leads to the partial
transfer of electron density from the central atom of
The aim of this work was to investigate the effect
of the degree of cobalt oxidation on the electrochemꢀ
ical and electrocatalytic properties of cobalt comꢀ
plexes of tetrakis(4ꢀmethoxyphenyl)porphyrin, finding
the kinetic parameters of oxygen reduction on elecꢀ
trodes modified with H2tetrakis(4ꢀmethoxyphenyl)porꢀ
the metal to the ꢀantibinding orbitals of the oxygen
π
molecule. Extracoordination is the initial stage of О2
reduction. The stability of oxygen extracomplexes of
metallic porphyrins depends strongly on the nature of
the second transpositioned extraligand.
phyrin (H T(pꢀMeOPh)P), tetrakis(4ꢀmethoxypheꢀ
2
II
nyl)porphyrinatocobalt(II) (Co Т(pꢀMeOPh)P), and
The electrochemical and electrocatalytic properꢀ (tetrakis(4ꢀmethoxyphenyl)porphyrinato)chlorocoꢀ
III
ties of porphyrins were studied in [1–7] in particular. balt(III) (Co Cl(T(pꢀMeOPh)P)). Investigating the
The authors of [3] investigated the effect of substituꢀ kinetic parameters of the oxygen reduction reaction is
9

10
TESAKOVA et al.
of particular interest both from the scientific standꢀ chromotographically purified (tetrakis(4ꢀmethoxyꢀ
point and for the substantiated selection of a catalyst. phenyl)porphyrinato)chlorocobalt(III) corresponded
to the literature data (
λ
max, nm/log , chloroform):
ε
5
83/4.02; 548/4.25; 433/5.61.
EXPERIMENTAL
The electrochemical and electrocatalytic properꢀ
The studied porphyrins were synthesized at the ties of porphyrins were investigated by means of cyclic
Faculty of Organic Chemistry, Ivanovo State Univerꢀ voltammetry in a 0.1 M solution of potassium hydroxꢀ
sity of Chemistry and Technology.
ide in an argon and oxygen atmosphere. Measureꢀ
ments were performed in a threeꢀelectrode electroꢀ
chemical cell. The main electrode was a graphitized
carbon rod whose side surface was insulated with a fluꢀ
orocarbon polymer shell. An extremely thin layer of
the active catalyst mass was deposited on the end surꢀ
face of the electrode, which was 8 mm in diameter.
The active mass of the catalyst consisted of industrial
elemental carbon (IEC) (TUꢀ14ꢀ7ꢀ24ꢀ80), a suspenꢀ
sion of fluorocarbon polymer, and the analyzed subꢀ
stance. A platinum electrode served as the polarizing
electrode. The obtained potentials are given with
respect to the reference silver chloride electrode.
The synthesis of tetrakis(4ꢀmethoxyphenyl)porꢀ
phyrin was accomplished by mixing 1.2 ml of a soluꢀ
tion (10.0 mmol) of anisic aldehyde in 15 ml of
nitrobenzene and 35 ml of propionic acid. Then 0.7 ml
(
10.0 mol) of pyrrole was added to the boiling mixture
and the obtained solution was boiled for 2 h. The
formed precipitate was cooled, filtered, washed with
methanol to complete the decolorizing of the wash
solution, and dried in the air at 70°С. The yield was
0
.82 g (44.6%). Purification was accomplished using
column chromatography on a silica gel (chloroform
being the eluent) with subsequent recrystallization
from the chloroform–hexane mixture. The obtained
product was in the form of large violet crystals. The
electron spectrum of the chromotographically purified
tetrakis(4ꢀmethoxyphenyl)porphyrin corresponded to
Cyclic voltamperegrams (CVAs) were obtained
using a PIꢀ50ꢀ1 potentiostate. The data were recorded
using a PC with preprocessing of the signal on an
interface device. The I–E curves were obtained in the
potential range of 0.5–1.5 V at potential scanning
rates of 5, 10, 20, 50, and 100 mV/s. To analyze and
assess the oxidation–reduction processes taking place
on the surface of the electrode with the investigated
substances, the I–E curves were recorded in electroꢀ
lyte saturated with argon and then with gaseous oxyꢀ
gen. The oxidation–reduction potentials of the proꢀ
cesses were calculated as the halfꢀsum of the potentials
of the cathode and anode maxima. The accuracy of
determining the potentials was 5 mV.
the literature data (
λ
max, nm/log
, chloroform):
ε
6
52/3.87; 595/3.78; 557/4.07; 520/4.25; 423/5.69).
Tetrakis(4ꢀmethoxyphenyl)porphyrinatocobalt(II)
was synthesized by adding 5.0 g (6.8 mmol) of tetꢀ
rakis(4ꢀmethoxyphenyl)porphyrin to a boiling soluꢀ
tion containing 5.0 g (20.1 mmol) of cobalt acetate tetꢀ
rahydrate in 150 ml of acetic acid. The mixture was
boiled for 0.5 h and kept at room temperature for 12 h.
The precipitate was filtered, washed with hot water, and
then dried in air at 70°С. The yield was 1.88 g (35%).
Purification was accomplished using column chromaꢀ
tography on a silica gel (chloroform being the eluent)
with subsequent recrystallization from the chloroꢀ
form–hexane mixture. The electron spectrum of the
chromotographically purified tetrakis(4ꢀmethoxypheꢀ
nyl)porphyrinatocobalt(II) corresponded to the literꢀ
RESULTS AND DISCUSSION
The electrochemical behavior of porphyrin comꢀ
pounds was studied using a metalꢀfree compound, tetꢀ
rakis(4ꢀmethoxyphenyl)porphyrin. There are two
maxima for this compound on the cathodic and
anodic sections of the potentiodynamic curve. Potenꢀ
ature data (
4
λ
max, nm/log , chloroform): 529/4.18;
ε
11/5.40.
To synthesize (tetrakis(4ꢀmethoxyphenyl)porphyꢀ tiodynamic scanning was performed in an argon
rinato)chlorocobalt(III), an air flow was passed atmosphere. The maximum corresponding to the
through a suspension (1.0 g, 1.26 mmol) of tetrakis(4ꢀ electroreduction of a porphyrin ligand with transfer of
methoxyphenyl)porphyrinatocobalt(II) in 250 ml of one electron and the formation of a monoanion is
methanol and 5 ml of concentrated hydrochloric acid observed on the cathodic branch in the potential range
for 10 h. The precipitate was filtered, the solution was of –0.6 to –0.8 V. On the anodic branch of the I–E
neutralized by a concentrated solution of ammonia, curve, the maximum of the reverse electrochemical
and evaporated in the vacuum of a waterꢀjet air pump process is observed in the potential range of –0.5 to
to 50 ml. After cooling, the precipitate of the complex –0.7 V. A second pair of maxima, corresponding to
was filtered, washed with water, and dried in air at the electroreduction of the porphyrin ligand with
room temperature. The yield was 0.5 g (47%). Purifiꢀ transfer of second electron and the formation of a
cation was accomplished using column chromatograꢀ dianion form, can be seen in the potential range of
phy on a silica gel (chloroform being the eluent) with –0.8 to –1.2 V. An increase in the scanning rate yields
subsequent recrystallization from the chloroform– a shift of the cathodic maxima toward more negative
hexane mixture. The obtained product was in the form potentials, while the anodic maxima are shifted
of large violet crystals. The electron spectrum of the toward more positive potentials.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 1 2012

KINETIC PARAMETERS OF THE ELECTROREDUCTION OF OXYGEN
11
Table 1. Potentials of the cathodeic and anodic maxima Ec, Ea of the oxidation–reduction potentials Ered/ox and the halfꢀ
peak potentials Em/2(O ) of the process of electroreduction on electrodes activated by the investigated compounds (V)
2
Сo3+
Co2+
Ered/ox
L
L–
L–
L2–
Compound
ꢀMеOPh)P
–
Em/2(O2)
Ec
Eа
–
Ec
–
Eа
–
Ered/ox
–
Ec
–Eа
–Ered/ox
H T(
2
р
–
–
–
0.680
0.630
0.630
–
0.540
0.600
0.610
–
0.585
0.615
0.620
–
1.100
1.130
1.180
–
0.960
1.010
1.010
–
1.030
1.070
1.095
–
0.290
0.190
0,160
0.300
II
Co T(
III
p
ꢀMeOPh)P
0.160
ꢀMeOPh)P) 0.140
–
0.230
0.300
–
0.195
0.220
–
Co Cl(T(
p
IEC
When using the electrode activated with tetrakis(4ꢀ studied compounds are effective catalysts in the reacꢀ
methoxyphenyl)porphyrinatocobalt(II) (Table 1), the tion of electroreduction of molecular oxygen. The
III
first maximum on the cathodic and anodic curves lies Co Cl(T(
pꢀMeOPh)P) complex is characterized by a
in the potential range of 0.1–0.3 V, which corresponds higher catalytic activity than H T(
pꢀMeOPh)P and
2
3+
2+
II
to the Со
↔
Со transition. The second maximum Co T(pꢀMeOPh)P (Table 1).
on the cathodic part of the curve in the potential range
of –0.6 to –0.7 V, along with that on the anodic part of
Figure 2 presents the CVA obtained at different
potential scanning rates for the processes taking place
on the electrode activated with Н2tetrakis(4ꢀmethoxyꢀ
phenyl)porphyrin. The maximum in the potential
range of –0.2 to –0.5 V corresponds to the process of
oxygen electroreduction. It can be seen from Fig. 3
that the maximum potential depends on the scanning
rate V. This, along with the absence of maxima during
the reverse (anodic) scan, points to the irreversibility
of the electrochemical reaction.
the curve in the potential range of –0.55 to –0.65 V,
–
correspond to the L
↔
L
transition. The third maxiꢀ
mum on the cathodic part of the curve in the potential
range of –1.1 to –1.2 V and that on the anodic part of
the curve in the potential range of –0.95 to –1.05 V is
–
2–
associated with the formation of the
form.
L
↔
L dianion
The same number of cathodic and anodic maxima
as in the case of tetrakis(4ꢀmethoxyphenyl)porphyriꢀ
natocobalt(II) is observed for the electrode containing
The obtained experimental data were quantitaꢀ
tively analyzed on the basis of the results from solving
the differential equation of nonstationary diffusion
with the corresponding boundary conditions in [9,
(
tetrakis(4ꢀmethoxyphenyl)porphyrinato)chlorocoꢀ
balt(III) in the active mass (Table 1). Table 1 lists the
redox potentials for all observed processes.
It was found in [8] that the oxidation/reduction of 10]. The potential of the maximum in the case of an
the central metal ion of cobalt porphyrin complexes irreversible electrode process linearly depends on ln
V:
2+
+
(
Сo
↔
Co ) and the first stage of electroreduction of
an organic ligand take place at close potential values.
The cathodic and anodic maxima observed for (tetꢀ
rakis(4ꢀmethoxyphenyl)porphyrinato)chlorocobalt(III)
and tetrakis(4ꢀmethoxyphenyl)porphyrinatocobalt(II)
in the potential range of –0.5 to –0.7 V are associated
with the superposition of the waves characteristic of
RT
E = B −
m
ln
(
αz V
α
)
,
(1)
2
αz F
α
I
, mА
3
1
2
two processes: Сo2+
+
–
−
1
0
1
↔
Co and
L
↔
L .
Saturation of the electrolyte with molecular oxygen
yields substantial variations in the shape of the
cathodic part of the I–E curve in the potential range of
–
0.1 to –0.4 V (Fig. 1), which corresponds to the
reduction of molecular oxygen. In this case, the signal
intensity increases as the electrolyte becomes satuꢀ
rated with dioxygen.
A comparative analysis of the electrocatalytic
activity of the studied compounds was performed
using the I–E curves corresponding to the limiting satꢀ
uration of the electrolyte with gaseous oxygen when no
changes in the shape of curves were observed during
further cycling (i.e., after electrolyte blowꢀthrough
with oxygen for 30–40 min).
0.4
0
−
0.4
−
0.8
−
1.2
−
E
1.6
, V
Fig. 1. CVA for electrodes activated with (
methoxyphenyl)porphyrin, tetrakis(4ꢀmethoxypheꢀ
nyl)porphyrinatocobalt(II), ( ) (tetrakis(4ꢀmethoxypheꢀ
nyl)porphyrinato)chlorocobalt(III) obtained by saturating
the solution with oxygen.
1) tetrakis(4ꢀ
(2)
3
Analysis of the halfꢀpeak potential Em/2(O2) at the
potential scanning rate
V = 0.02 V/s indicates that the
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 1 2012

12
TESAKOVA et al.
It follows from Eq. (1) that the tangent of the incliꢀ
I
, mА
5
4
3
nation of line Em(ln allows us to calculate transfer
V)
2
−
2
0
2
coefficient , since z = 1 (as a rule). Analysis of the
α
α
1
obtained experimental data showed that the depenꢀ
dences of Em(ln for our investigated electrocatalytic
systems were linearized with the correlation coeffiꢀ
V)
2
cient
are listed in Table 2, which also gives the values for
the Tafel’s slope calculated using the equation
R = 0.90–0.99 (Fig. 3). The calculated values of
α
b
0.4
0
−
0.4
−
0.8
−1.2
2
zαF
.3RT
E
, V
,
(3)
b =
II
Fig. 2. CVA for the electrode activated with tetrakis(4ꢀ
methoxyphenyl)porphyrin at different rates of potential
scanning: (
where
MeOPh)P,
values of
follow from our analysis of the cathodic branch of the
CVA (Fig. 1). For the electrode activated with H T(
z = 2 for H T(pꢀMeOPh)P and Co T(pꢀ
2
III
z
= 4 for Co Cl(T(
pꢀMeOPh)P). These
1
) 0.005, (
2
) 0.01, (
3
) 0.02, (
4
) 0.05, and
z
(the number of electrons in the reaction)
(5) 0.10 V/s.
pꢀ
2
Em, V
II
1
2
3
MeOPh)P and Co T(pꢀMeOPh)P, we may assume
that the first maximum in the potential range of –0.1
to –0.4 V is associated with the first stage of oxygen
reduction with the participation of two electrons and
the formation of a peroxide ion:
−
0.4
0.2
0
−
О + Н О + 2e → HO2 + ОН–.
2
2
−
The second maximum in the potential range of –0.4 to
0.8 V corresponds to the subsequent reduction of the
peroxide ion:
–
−
HO2 + Н О + 2e → 3ОН–.
2
The existence of only one maximum on the cathodic
part of curve (the absence of the maximum in the
3
4
5
3
−lnV
potential range of –0.4 to –0.8 V) depends on the
fourꢀelectron process of oxygen reduction with the
Fig. 3. Dependence of Em(ln
deposited active mass containing (
V
)
for the electrodes with
H T( ꢀMeOPh)P,
CoIIICl(T(
(2) Co T(pꢀMeOPh)P, (3) pꢀMeOPh)P).
1)
p
formation of a hydroxylꢀion for the electrode activated
2
III
II
by Co Cl(T(
pꢀMeOPh)P):
О + 2Н О + 4e → 4ОН–.
2
2
where
temperature,
fer coefficient, and
stage determining the reaction rate. The term
depends on the stationary constant of the electroꢀ
chemical reaction rate k0 and the oxygen diffusion
coefficient in the solution
lated using the equation
R
is the universal gas constant,
is the Faraday constant,
is the number of electrons at the
T
is the absolute
Similar results were obtained on a rotating disc elecꢀ
trode with ring [11], demonstrating that the yield of
hydrogen peroxide on most macroheterocyclic comꢀ
pounds in an alkali solution is negligible. In this case,
the fourꢀelectron process with the formation of a
hydroxyl ion can take place, though successive twoꢀ
electron processes with the rapid reduction of the perꢀ
oxide ion are also possible [11, 12].
F
α
is the transꢀ
z
α
B
D. At 298 K, it can be calcuꢀ
Parameter
value of the cross section intersected by the line
Em(ln on the ordinate axis. Using Eq. (2) and the
oxygen diffusion coefficient
B in Eq. (1) can be determined from the
1
⎡
k
0
⎤
B =
−0.067 + 0.026 ln
.
⎥
(2)
⎢
αz ⎣
α
D⎦
V
)
–
5
2
D
= 2.601 × 10 cm /s
Table 2. Kinetic parameters of oxygen reduction on elecꢀ [13], we can calculate the stationary constant of the
trodes containing the investigated compounds contained in
electrochemical reaction. It follows from Table 3 that
the active mass
Compound
ꢀMeOPh)P
III
the values of k0 decline in the series Co Cl(T(
pꢀ
II
3
k0
× 10 ,
m/s
–
E1/2
V
,
MeOPh)P) > Co T(
p
ꢀMeOPh)P > H T(
2
p
ꢀMeOPh)P.
α
b, V
Another parameter that characterizes the electroꢀ
catalytic activity of the surface compound is the halfꢀ
wave potential (E1/2) of the corresponding process. In
the case of an irreversible reaction, however, the
potential of the maximum (the halfꢀpeak potential
H T(
p
0.241 0.123 0.166 0.255
0.261 0.113 0.315 0.182
2
II
Co T(
III
p
ꢀMeOPh)P
Co Cl(T(pꢀMeOPh)P) 0.255 0.058 0.504 0.138
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 1 2012

KINETIC PARAMETERS OF THE ELECTROREDUCTION OF OXYGEN
13
Em/2) depends on the scanning rate
E1/2 were therefore determined by extrapolating the
dependences to = 0, with allowance for the
V
. The values of
REFERENCES
1.
Porphyrins: Spectroscopy, Electrochemistry, Application
Ed. by N. S. Enikolopyan (Nauka, Moscow, 1987) [in
Russian].
,
Em/2
(
V
)
V
nonꢀFaraday current of the double electric layer chargꢀ
ing. The DEL charging current was found as a rectilinear
continuation of the initial section of the voltammetric
curve. It follows from Table 2 that the above mentioned
2. M. R. Tarasevich, K. A. Radyushkina, and G. V. Zhuꢀ
taeva, Russ. J. Electrochem. 40, 1174 (2004).
3. G. V. Zhutaeva, M. R. Tarasevich, M. V. Radina, and
III
II
series of Co Cl(T(
H T( ꢀMeOPh)P holds for the halfꢀwave potential
values as well.
p
ꢀMeOPh)P) > Co T(
p
ꢀMeOPh)P
>
I. S. Chernyshova, Russ. J. Electrochem. 45, 1080
(2009).
p
2
4
. M. I. Bazanov, Izv. Vyssh. Uchebn. Zaved., Khim.
Khim. Tekhnol. 31 (6), 62 (1988).
5
. K. M. Kadish, K. M. Smith, and R. Guilard, The Porꢀ
phyrin Hand Book (Academic, San Diego, 2000),
Vol. 9, p. 150.
CONCLUSIONS
6
. V. A. Bogdanovskaya, L. A. Beketaeva, K. V. Rybalka,
et al., Russ. J. Electrochem. 44, 293 (2008).
The results of our investigations show that among
the analyzed macroheterocyclic compounds, the
III
7. M. R. Tarasevich and K. A. Radyushkina, Usp. Khim.
, 1498 (1980).
8. D. A. Filimonov, O. V. Samoletov, M. I. Bazanov, et al.,
Elektrokhim. Energet. (2), 91 (2009).
Co Cl(T(pꢀMeOPh)P) complex is characterized by
49
the greatest electrocatalytic activity, relative to the
II
Co T(
pꢀMeOPh)P complex and the metalꢀfree
9
H T( ꢀMeOPh)P complex. This is likely due to the
p
2
9. V. S. Bagotskii, Principles of Electrochemistry (Khimiya,
charge of the complex being able to change (the forꢀ
mation of ionic forms) upon variations in the electrode
potential during electrochemical reactions, which
leads to changes in electrocatalytic activity.
Moscow, 1988) [in Russian].
1
0. L. F. Kozin, Electrodeposition and Dissolution of Multiꢀ
valent Metals (Naukova Dumka, Kiev, 1989) [in Rusꢀ
sian].
1
1. M. R. Tarasevich and K. A. Radyushkina, Catalysis and
Electrocatalysis by Metalloporphyrins (Nauka, Moscow,
1982) [in Russian].
ACKNOWLEDGMENTS
1
2. M. I. Bazanov, A. V. Petrov, G. V. Zhutaeva, et al., Russ.
The authors are deeply grateful to Professor
A.S. Semeikin for synthesizing the investigated porꢀ
phyrins.
J. Electrochem. 40, 1198 (2004).
13. N. R. Elizovic, B. M. Babic, Lj. M. Vracar, and
N. V. Krstajic, J. Ser. Chem. Soc. 72, 699 (2007).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 1 2012