1070-4272/03/7607-1067$25.00C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 7, 2003, pp. 1067!1069. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 7,
2003, pp. 1099!1102.
Original Russian Text Copyright + 2003 by Ivanova, Ivanov, Boldyrev, Makeeva, Sokol’skii.
AND CORROSION PROTECTION OF METALS
Thin-Film Cathode Materials Based on Chromium Oxides
N. D. Ivanova, S. V. Ivanov, E. I. Boldyrev, I. S. Makeeva, and G. V. Sokol’skii
Vernadsky Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
National Aviation University, Kiev, Ukraine
Received April 25, 2002; in final form, May 2003
Abstract-The possibility of cycling of thin (8310 mm) films of chromium oxide compounds was studied.
The charging3discharge conditions were optimized.
In the recent decade, much attention has been given
to thin-film materials for primary and secondary
chemical power sources (CPS) [1, 2]. Such materials
are promising electrodes for unconventional (flexible)
CPS. Flat CPS are used in laptops, credit cards, opti-
cal displays, solar batteries, etc. Also, thin-film elec-
trodes have aroused specific interest for rechargeable
power sources. In such sources, protons or ions dif-
fuse for a short distance, and the charging3discharge
processes are short compared to pelletized electrodes.
Many materials are used as CPS electrodes: metal
oxides, chalcogenides, and some polymers. Among
them, the oxide materials are the most environmental-
ly acceptable and convenient in use; they also have
high specific electrical characteristics .
When choosing the oxide compound for CPS elec-
trode, it should be taken into account that the incor-
poration of the corresponding ion (Li
must change the unit cell volume of the oxide by no
more than approximately 20%. If this value exceeds
20% (as, e.g., 38% for CrO
and 33% for MnO
then the ion incorporation is irreversible  (this also
refers to lithium ion).
A cathode material for secondary CPS must be cap-
able of recovery, i.e., discharge in the cathodic cycle
and charging in the anodic cycle. Thus, in the ideal
case, the lithium ion incorporation into, and removal
from the crystal lattice must be reversible to the extent
as maximal as possible. As shown in , the higher
the diffusion rate, the easier are the charging3dis-
charge processes in the system. The mass-transfer rate
is considerably higher in oxide compounds with the
disordered structure . For this reason, nonstoi-
chiometric oxide compounds are of undoubted interest
[6, 7]. It was shown that, in such compounds, the rate
of electrochemical processes is considerably higher
(sometimes by several orders of magnitude) than in
stoichiometric compounds. For example, stoichiomet-
ric chromium oxide CrO
is unsuitable for secondary
power sources , whereas the nonstoichiometric
oxide is a promising electrode material .
Powders and films of nonstoichiometric oxide
compounds of a series of transition metals can be pre-
pared by an electrochemical procedure developed pre-
viously . Use of such compounds as a cathode of
primary CPS increases the rate of electrochemical pro-
cesses, which is manifested as a considerable increase
in the current density of pelletized electrodes .
The goal of the work was to examine the possibil-
ity of using thin-film chromium oxide compounds as
cathodes and to find how the extent of reversibility of
the charging3discharge process depends on the com-
pound composition (degree of nonstoichiometry).
The test objects were chromium oxide compounds
differing in the degree of nonstoichiometry. Films of
chromium oxide compounds were prepared from an
electrolyte containing 2.5 M CrO
. To vary the com-
pound composition, 0.1, 0.2, 0.3, or 0.4 M fluoride
ions were introduced as ligands. The electrolyte tem-
perature did not exceed 30+ 0.1oC, and the current
density was 50 A dm
Films of different compositions were deposited
onto electrodes made of 1Cr18Ni10Ti stainless steel.
The electrode area was 0.25 cm
. The film thickness
was 8310 mm depending on the electrolysis time.
A film more than 4 mm thick is nonporous, which ex-
cludes the contact of the support with the electrolyte.
As electrolyte, we used 1 M KOH. The tests were
performed at room temperature. Platinum (surface