ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 8, pp. 1341!1345. + Pleiades Publishing, Ltd., 2007.
Original Russian Text + G.A. Kolyagin, V.L. Kornienko, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 8, pp. 1302!1306.
AND CORROSION PROTECTION OF METALS
Double Layer Capacitance of Gas-Diffusion Electrodes
Made of Acetylene Black and Expanded Natural Graphites
and Evaluation of the Surface Area Wetted
by the Electrolyte
G. A. Kolyagin and V. L. Kornienko
Institute of Chemistry and Chemical Technology, Siberian Division, Russian Academy of Sciences,
Received December 26, 2006
Abstract-Cyclic voltammetry was used to determine the capacitance of the double layer in hydrophobized
porous gas-diffusion electrodes made of acetylene black and expanded natural graphites. The average radius
of pores by with an alkaline electrolyte, the area of these pores, and the true current density in electro-
reduction of oxygen were evaluated.
It is known that carbon-graphite materials and com-
posites on their base are widely used as construction
materials and electrodes  in various electrochemical
devices employing aqueous electrolyte solutions: elec-
trolyzers, power cells, electrochemical sensors , and
capacitors [33 6]. In most cases, these materials have
a pronounced porosity and highly developed internal
surface. A knowledge of their structural characteristics
and dynamics of their interaction with aqueous solu-
tions is necessary for improvement of articles fabri-
cated from these materials.
One of methods used to study and determine
the structural characteristics of electrically conducting
porous materials impregnated with an electrolyte so-
lution is cyclic voltammetry (CVA) with linear poten-
tial sweep [7, 8313]. This method is convenient in
that, with a knowledge of the specific capacitance of
materials under study, one can rapidly obtain neces-
sary evidence concerning the interaction of porous
bodies with a liquid medium under real operation con-
ditions of electrodes without their disintegration or
any change in their characteristics. If the specific
capacitance of a material under study is unknown,
the relative effects of various factors on the true work-
ing surface area of electrodes can be evaluated. For ex-
ample, it was shown in  that the electric activity
of carbon materials is proportional to the surface area
evaluated by CVA, rather than to that given by BET.
Recently, CVA has been frequently used to study ex-
panded natural graphites (ENG) and fibers and articles
made of these materials. For example, the possibil-
ity of using CVA to study articles made of ENG
with a thickness of 236 mm and density of 1603
470 g dm
at a potential sweep rate of 0.2350 mV s
in order to determine the surface area, average pore
radius, and porosity was demonstrated in .
It can be assumed that, under conditions of partial
wetting of a porous body by water (porous hydro-
phobized gas-diffusion electrodes, electrically con-
ducting composite materials, etc), CVA can be used
to determine the surface area wetted by an aqueous
solution. It is known that the activity of gas-diffusion
electrodes strongly depends on the surface area wetted
by the aqueous electrolyte; the knowledge of this
parameter is necessary both for theoretical calculations
and for applied studies, e.g., in finding the rate-de-
termining stage of the process of current generation
in the electrode.
This study continues research in the field of ENG-
based hydrophobized gas-diffusion electrodes .
The aim of the study was to evaluate the surface area
of hydrophobized gas-diffusion electrodes, wetted
by an aqueous solution, by the CVA method and to
correlate this surface area with the activity of elec-
trodes in electroreduction of oxygen. To compare
ENG with other carbon materials, electrodes fabri-
cated from A-437E acetylene black with a specific
surface area of 100 m
were also studied.