Electrolytic synthesis of binary oxide systems based on manganese(II) oxide

Article abstract of DOI:10.1023/A:1016195932684

Joint anodic deposition of manganese, cobalt, nickel, and chromium oxides, which form binary oxide systems, from two-component sulfate solutions of the constituent metals was studied under different electrolysis conditions.

Full text of DOI:10.1023/A:1016195932684

Russian Journal of Applied Chemistry, Vol. 75, No. 2, 2002, pp. 213 218. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 2, 2002,
pp. 221 226.
Original Russian Text Copyright
2002 by Nagirnyi, Apostolova, Baskevich, Litvin, Shembel’.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Electrolytic Synthesis of Binary Oxide Systems
Based on Manganese(II) Oxide
V. M. Nagirnyi, R. D. Apostolova, A. S. Baskevich, P. M. Litvin, and E. M. Shembel’
Ukrainian State University of Chemical Engineering, Dnepropetrovsk, Ukraine
Received January 15, 2001
Abstract Joint anodic deposition of manganese, cobalt, nickel, and chromium oxides, which form binary
oxide systems, from two-component sulfate solutions of the constituent metals was studied under different
electrolysis conditions.
Multicomponent oxide systems of the type LiCox
Mn2 xO4, LiCoyMn2 yO4, and MnV2O5, prepared by
under varied electrolysis conditions. Data of this kind
are unavailable in the literature.
The electrolysis was performed in a 0.2-dm3 tem-
perature-controlled glass cell. Smooth plates of tech-
nical grade VT-1 titanium served as a cathode. The
oxides under study were deposited as compact coat-
ings on two sides of gauze and plate-like 12X18H9T
steel anodes of size 10 10 0.15 and 10 10
0.3 mm, respectively, at Sa : Sc = 1 : 5. An X-ray dif-
fraction analysis was used to study on disperse deposits
of weight 0.1 0.15 g, obtained on a smooth VT-1
titanium plate. The solutions were prepared from pure
and analytically pure reagents and distilled water.
Two-component solutions based on manganese, co-
balt, nickel, and chromium sulfates were used in the
study. The total concentration of the solutions stud-
ied was within the range 0.3 0.4 M at a ratio of
the main to doping components from 5 : 1 to 1 : 5.
All runs were performed at 85 3 C and pH 2.0 2.5.
The electrolysis parameters were chosen on the basis
of preliminary experimental tests. The deposition rate
doping of traditional electrochemically active oxides
of manganese, vanadium, etc., are of interest for
developing efficient cathode materials for lithium
batteries [1 4]. Such materials are mainly prepared
by chemical-thermal synthesis of stoichiometric mech-
anical mixtures of thermally unstable salts of the cor-
responding metals (with simultaneous modification
of the forming oxide compounds in the presence of
lithium carbonate or hydroxide, if necessary). The es-
sential drawback of this method is the difficultly
controllable synthesis and the contamination of the
final product with impurities formed in side reactions.
This makes preferable the electrochemical synthesis
of complex oxide systems by anodic deposition from
aqueous solutions containing salts of co-deposited
metals [5, 6]. The electrolytic synthesis is advantage-
ous because of the possibility of preparing homogene-
ous materials, whose components, unlike the case of
mechanical mixtures, have related structures and can
interact at the molecular level. Along with this, the
electrochemical method allows fabrication ballast-
free cathodes by direct deposition of complex oxide
systems onto a smooth or gauze stainless-steel sub-
strate. Vanadium(V) oxide, synthesized simultane-
ously with manganese oxide, shows better electro-
chemical performance than the individually synthe-
sized material [7].
1
Vdep (mg cm 2 h ) was determined from the weight
gain upon electrolysis per unit surface per unit time.
Polarization curves were taken in a special three-
chamber cell on a plate-like 12X18H9T steel anode
(Sa = 1 cm2) with surface roughness corresponding
to
7 8 at Sa : Cc = 1 : 4 and current densities in
2
the range 0.5 50 mA cm . The potentials were mea-
sured relative to a silver chloride reference electrode
(E = +0.225 V) with a ShCh-4315 digital voltme-
ter. The X-ray diffraction analysis was done on a
DRON-2 diffractometer. The microstructure of the
surface of deposits (1 3.5 m thick films) was stud-
ied with a nanoscope. The quantitative composition
Therefore, it was appropriate to study the pos-
sibility of preparing complex binary systems by joint
electrolytic deposition of oxide compounds of man-
ganese, cobalt, nickel, and chromium from mixed
aqueous solutions of salts of metals co-deposited
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214
NAGIRNYI et al.
Mn2+ + 2H2O
MnO2 + 4H+ + 2e,
Co2O3 + 6H+ + 2e,
E0 = 1.23 V,
(2)
(3)
(4)
(5)
2Co2+ + 3H2O
2Ni2+ + 3H2O
E0 = 1.8 V,
Ni2O3 + 6H+ + 2e,
NiO2 + 4H+ + 2e,
E0 = 1.75 V,
Ni2+ + 2H2O
E0 = 1.68 V,
2Cr3+ + 3H2O
2CrO3 + 6H+ + 6e,
Fig. 1. Deposition rate V
of binary oxides vs. the con-
E0 = 1.36 V,
(6)
(7)
(8)
dep
centration ratio of sulfates of co-deposited metals C (M).
Total concentration 0.3 0.4 M, T = 85 C, pH 2.0 2.2,
2
Ni2O3 + Mn2O3
2CrO3 + 3Mn2O3
2NiO + 2MnO2,
Cr2O3 + 6MnO2.
i = 15 mA cm ; the same for Fig. 4. System: (1) Mn Co,
a
(2) Mn Ni, and (3) Mn Cr.
of the deposits was estimated approximately by the
oxalate technique chemical analysis [8].
Reactions (1) (6) are related to standard redox sys-
tems. The standard electrode potentials for these reac-
tions are given according to the data of [9, 10]. How-
ever, only reactions (1) (3) can actually occur under
the conditions considered. In the given case, reactions
(4) (6) are concurrent and can proceed to give oxide
compounds only simultaneously with manganese ox-
idation. Reactions (7) and (8) are quite permissible,
with account taken of the probable ionic and inter-
phase interaction of conjugate components in anodic
deposition under certain conditions. This is confirmed
by X-ray diffraction analysis of the corresponding
binary systems, in which the presence of all of the
oxide phases described by equations (1) (4) and (6)
(8) was revealed [reaction (5) is intermediate].
Figure 1 shows how the deposition rate of the sys-
tems studied varies with the ratio of the main com-
ponents in mixed solutions under the indicated condi-
tions of electrolysis. With increasing dopant con-
centration in a solution, the deposition rate gradually
decreases in all cases. Comparison of the deposition
rates of individual manganese and cobalt oxides from
their solutions under comparable conditions of elec-
trolysis (20 25 and 2.5 3.0 mg cm 2 h , respective-
1
ly) shows that the efficiency of the anodic process
decreases steadily with increasing dominating role of
delayed formation of the doping phase in the anodic
deposit (Fig. 1, curve 1). Similar dependences were
obtained for the systems Mn Ni and Mn Cr. How-
ever, the deposition rate for these systems decreases
more sharply with increasing dopant concentration
(Fig. 1, curves 2, 3). This is accounted for by the fact
that, under the given conditions, nickel and chromium
oxides cannot be deposited directly from their solu-
tions, and are co-deposited with manganese oxide
onto the anode. Apparently, the forming manganese
oxide acts as a catalyst, energetically facilitating the
transition of the conjugate metal ions into the oxide
phase and the formation of stable oxide compounds
in the joint anodic process.
Probably, processes of joint deposition of the oxide
systems studied may occur stage by stage or follow-
ing other, more complex schemes. This is indirectly
confirmed by comparative analysis of the ia E depen-
dences characterizing the process of joint deposition
(Fig. 2). A characteristic feature of these dependences
is the presence of an intermediate plateau at potentials
preceding the ascending branch. The relative position
and the character of the corresponding curves depend
on the manganese to metal salt concentration ratio
Mn : M (where M is Co, Ni, and Cr) in solution.
It can be seen in Fig. 2 that raising the dopant
concentration makes the anodic polarization stronger
and the current density lower. In this case, the rel-
ative shift of the upper portions of polarization curvers
for the same binary system at the concentration ratio
in solution varied from 3 : 1 to 1 : 3 is 0.23 0.25 V,
The feasible anodic reactions corresponding to the
systems studied can be represented by equations (1)
(6) [9, 10] and concurrent redox reactions (7), (8):
2Mn2+ + 3H2O
Mn2O3 + 6H+ + 2e,
E0 = 1.0 V,
(1)
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ELECTROLYTIC SYNTHESIS OF BINARY OXIDE SYSTEMS
and that of the lower portions at the level of the in-
215
flection points, no more than 0.1 V. At current den-
sities lower than 5 mAcm 2 the curves virtually merge
together, irrespective of the above ratio.
The influence exerted by the nature of a doping
component is manifested as enhancement of the anod-
ic polarization in order Co < Ni < Cr, in agreement
with the dependences of the deposition rate on the
Mn : M ratio in solution (Fig. 1). Comparison of the
lower portions of the ia E curves for binary systems
with a similar dependence of the anodic deposition of
manganese oxide from its solutions shows that oxida-
tion of manganese to give oxide is the potential-de-
termining process, irrespective of the Mn : M ratio.
This process is accompanied by simultaneous reac-
tions of binary oxide formation and hydrogen evolu-
tion, which are more intensive in the range of the
upper ascending branches of the curves.
Fig. 2. Current voltage characteristics of anodic formation
of (1) manganese and (2) cobalt oxides from their solu-
tions and binary oxides from mixed sulfate solutions of
co-deposited metals at concentration ratios (3 5) 3 : 1 and
(3 5 ) 1 : 3. Total concentration 0.3 0.4 M, T = 85 C,
pH 2.0. (i ) Current density and (E) potential. System:
(3, 3 ) Mn Co, (4, 4 ) Mn Ni, and (5, 5 ) Mn Cr.
Probably, the less positive anode potentials in the
lower portions of the curves result from the occur-
rence of reactions of the first stage of magnesium ox-
a
idation Mn2+
Mn3+ and oxygen discharge on the
initial weakly oxidized stainless-steel surface, pro-
ceeding with lower energy expenditure. After a solid
oxide film is formed on the anode and the limiting
diffusion current of the co-deposited metal ions is
reached, the process passes into a new stage (upper
portions of the curves), with the corresponding change
in the relative rates of the concurrent anodic reactions:
O2 > oxide(Mn M). The energy balance of the anodic
process as a whole is determined by the polarization
of electrode reactions invilving oxygen evolution on
the anode surface shielded by a solid oxide film and
of co-deposition of oxide compounds of the conjugate
oxide system. In this case, raising the concentration
of the doping phase causes a corresponding increase
in the anodic polarization. This follows from a com-
parison of the upper portions of the curves for the sys-
tems with Mn : M ratio higher and lower than unity
(Fig. 2, curves 3, 3 ; 4, 4 ; 5, 5 ). As seen, the upper
portions of curves 3 5 lie at more positive potentials
than the corresponding portion for deposition of co-
balt oxide from its solution.
Fig. 3. Deposition rate V
of the double oxide Mn Cr vs.
dep
anodic current density i at various C
: C
a
MnSO4
Cr2(SO4)3
ratios. Total concentration 0.3 0.4 M, T = 85 C, pH 2.0
2.5. C : C : (1) 5 : 1, (2) 3 : 1, (3) 1 : 1,
MnSO4
Cr2(SO4)3
(4) 1 : 3, and (5) 1 : 5.
sity, observed for the binary systems studied at var-
ious Mn : M ratios (for the example of the Mn Cr
system; Fig. 3). The dependences are similar for all
Mn : M ratios: the deposition rate sharply increases
in a narrow range of current densities and reaches
The current density on the surface preliminarily
coated with a solid film of the corresponding binary
oxide steadily grows with increasing potential and re-
aches the limiting values for the given binary system
without intermediate plateaus (Fig. 2, curve 5, dashed
line). This confirms the considered kinetic origin of
the electrode processes studied at different current
densities. The last assumption is in accord with the
dependences of the deposition rate on the current den-
2
certain limiting values at ia = 15 20 mA cm . In this
case, the limiting values of Vdep totally coincide with
the corresponding values in the dependence of the de-
position rate on the Mn : M ratio at constant current
density (Fig. 1, curve 3) and decrease at higher
dopant concentrations.
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216
NAGIRNYI et al.
position on the anode. These compound correspond
to the most thermodynamically stable forms: MnO2,
CoO, Co3O4, NiO, Ni2O3, and Cr2O3 (Fig. 4). These
systems are the most reliably identified by diffractom-
etry at Mn : M = 3 : 1 and after high-temperature treat-
ment at 400, 650, and 720 750 C. Simultaneous
modification of the obtained complex oxides in the
presence of lithium hydroxide or carbonate is a pre-
requisite to synthesis of electrochemically active oxide
systems in the form of double spinels of the type
LiCoxMnO2 xO4, LiCryMnO2 yO4, etc.
Presently, the origin of the structural and molecular
correlation in the bulk between the systems studied is
unclear. A certain information can be obtained from
a comparative analysis of the microstructure and
microrelief of the surface of thin-film coatings of the
corresponding oxides, deposited onto a smooth stain-
lesssteel substrate at Mn : M = 1 : 2 (Fig. 5).
Fig. 4. Diffraction patterns of binary oxides (1) Mn Ni,
(2) Mn Co, and (3) Mn Cr, deposited from solutions
with concentration ratios C : C = 1 : 3 and
MnSO4
MSO4
Analysis of the presented data shows that the struc-
tures of individual oxides and mixed oxides differ
significantly. For example, photomicrographs of the
surface of the deposits, taken under the same magnif-
ication, show that the structure of manganese oxide is
coarsely grained crystalline with typical layer-by-layer
growth of separate grains (Fig. 5a). At the same time,
the cobalt oxide structure is more finely grained, with
random orientation of crystals (Fig. 5b).
heated in air to 420 C for 7 h. (I/I ) Relative intensity
and (2 ) Bragg angle.
0
After the limiting values are reached, the deposi-
tion rate gradually decreases with increasing current
density, which is due to the growing contribution
to the energy balance of the anodic process from the
hindered reaction of doping phase formation and to
the increasing fraction of joint oxygen evolution. This
circumstance is in agreement with the current voltage
characteristics of the anodic formation of the corre-
sponding binary systems (Fig. 2). Apparently, the
fraction of the doping phase in the binary deposit
must grow in the given case.
The structure of co-deposited manganese and co-
balt oxides in a mixed anodic deposit essentially dif-
fers from the structure of the individual oxides in
that a peculiar pattern of finely grained randomly
distributed combs is formed, which makes the spe-
cific surface area of the deposits considerably larger
(Fig. 5c).
Such an increase also takes place when the Mn : M
ratio in solution is changed toward increased concen-
trations of the concurrent component. For example,
approximate quantitative estimate of the composition
of the binary Mn Co oxide shows that, with the
Mn : Co ratio in solution changed from 1 : 2 to 1 : 3,
the content of cobalt oxide in the deposit may increase
from 12 15 to 20 wt %. For the Mn Ni and Mn Cr
systems, these values are lower: 10 12 and 5 8 wt %,
respectively. Similar relationships are retained for
all of the systems studied When the total concentra-
tions of the corresponding components in solution are
raised, with other electrolysis conditions being the
same. However, at Mn : M < 1 (1 : 2, 1 : 3, etc.) and
Deposits with a similar structure are also obtained
in joint deposition of manganese and nickel oxides.
This is possibly due to the similar mechanisms of
formation of the double systems under consideration
(Fig. 5d), governed by the interaction of conjugate
phases in the stage of their formation and crystalliza-
tion into grains.
Unlike these systems, Mn Cr oxide is obtained on
the anode in the form of finely grained columnar de-
posit with rather developed surface (Fig. 5e). These
deposits are characterized by ordered structure with
virtually symmetric alternation of nearly identical
valleys and ridges. Apparently, the mechanism of nu-
cleation and interaction of molecules of the conjugate
phases is more intensive in this system, compared
with deposition of the binary oxides considered in
the present study. This impedes growth of manganese
1
total concentration above 100 g l , the deposition rate
decreases considerably owing to the increased contri-
bution of the hindered formation of the doping phase.
According to the results of X-ray diffraction ana-
lysis, the materials studied are two-phase systems
consisting of oxide compounds formed by joint de-
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ELECTROLYTIC SYNTHESIS OF BINARY OXIDE SYSTEMS
(a) (b)
217
(c)
(d)
(e)
Fig. 5. Photomicrographs of the surface of the electrolytic deposits of (a) MnO , (b) Co O , and binary oxides (c) Mn Co,
2
2 3
(d) Mn Ni, and (e) Mn Cr obtained from solutions with 1 : 2 concentration ratio of sulfates of co-deposited metals.
oxide crystals and facilitates their degeneration in the
early stage of development.
These data suggest that, from the standpoint of
energetics, the binary oxides studied are a certain in-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 2 2002

218
NAGIRNYI et al.
termediate system between a homogeneous mechan-
ical mixture and the single-phase chemical compound.
tal’nye problemy electrockhimicheskoi energetiki
(IV Int. Conf. Fundamental Problems of Electro-
chemical Energetics ), Saratov (Russia), June 21 23,
1999, pp. 75 77.
CONCLUSIONS
2. Kachibaya, E.I, Imnadze, R.A., Pankidze, T.V., et al.,
Abstracts of Papers, IV Mezhdunarodnaya konferen-
tsiya Fundamental’nye problemy electrockhimiches-
koi energetiki (IV Int. Conf. Fundamental Problems
of Electrochemical Energetics ), Saratov (Russia),
June 21 23, 1999, pp. 55 56.
3. Zhang, F., Zavalij, P., and Wittingham, M.S., Electro-
chem. Commun., 1999, no. 1, pp. 564 567.
4. Baudrin, E., Laruelle, S., Denis, S., et al., Solid
Ionics, 1999, vol. 123, pp. 139 153.
(1) It was demonstrated that complex oxide sys-
tems, showing promise as active supports for effi-
cient cathodes of lithium batteries, can be obtained
in various combinations (Mn Co, Mn Ni, Mn Cr,
etc.) by electrolysis of two-component solutions of
Mn(II), Co(II), Ni(II), and Cr(III) sulfates at certain
ratios of their concentrations and certain electrolysis
parameters.
5. Shembel’, E.M., Apostolova, R.D., and Nagirnyi, V.M.,
(2) The necessary condition for electrolytic syn-
thesis of such materials is the presence of a base ox-
ide material, which can be deposited individually on
the anode in reasonably high yield, e.g., manganese
and cobalt oxides.
Elektrokhimiya, 2000, vol. 36, no. 1, pp. 41 48.
6. Shembel, E.M., Apostolova, R.D., Nagirny, V.M., et al.,
Abstracts of Papers, The 197th Meet. of the Electro-
chem. Society, Toronto (Canada), 2000, p. 105.
7. Le Gal La Salle, A., Guyomard, D., Verbaerre, A.,
and Piffard, Y., Abstracts of Papers, 9th Int. Meet. on
Lithium Batteries, Edinburg (Scotland), 1998,
poster II, Thursday, no. 91.
8. Kolthoff, I.M., Belcher, R., Stenger, V.A., and
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Wiley, 1957.
9. Spravochnik po elektrokhimii (Handbook of Electro-
chemistry), Sukhotin, A.M., Ed., Leningrad: Khimiya,
1981.
(3) Of particular interest are binary oxides of the
series studied, synthesized from solutions at 2 : 1
1 : 3 concentration ratios of the main to doping
metal salts at average total concentration of 0.3
0.4 M. The electrolysis parameters are as follows:
temperature 80 85 C, pH 2.0 2.5, and anodic cur-
2
rent density 7.5 25 mA cm .
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 2 2002