Pilot laboratory electrolyzer for electrosynthesis of hydrogen peroxide in acid and alkaline solutions

Article abstract of DOI:10.1134/S1070427211010113

Results of a preparative electrosynthesis of hydrogen peroxide by cathodic reduction of oxygen in a carbon black gas-diffusion electrode in acid and alkaline electrolyte solutions in a versatile pilot laboratory three-chamber electrolyzer are presented.

Full text of DOI:10.1134/S1070427211010113

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 1, pp. 68−71. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © G.A. Kolyagin, V.L. Kornienko, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 1, pp. 68−71.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Pilot Laboratory Electrolyzer for Electrosynthesis of Hydrogen
Peroxide in Acid and Alkaline Solutions
G. A. Kolyagin and V. L. Kornienko
Institute of Chemistry and Chemical Technology, Siberian Branch,
Russian Academy of Sciences, Krasnoyarsk, Russia
Received March 18, 2010
Abstract—Results of a preparative electrosynthesis of hydrogen peroxide by cathodic reduction of oxygen in
a carbon black gas-diffusion electrode in acid and alkaline electrolyte solutions in a versatile pilot laboratory
three-chamber electrolyzer are presented.
DOI: 10.1134/S1070427211010113
Hydrogen peroxide as a high-potential redox agent
possesses a number of unique properties. It is well
soluble in water and nonpoisonous. No dangerous waste
is formed upon its application because its decomposition
yields water and oxygen. Hydrogen peroxide has a
considerable oxidizing capacity and enables oxidation
of various organic and inorganic compounds in both
alkaline and acid media: E°H2O2/H2O = 1.776 V in
acid media and E°H2O2/OH– = 0.88 V in alkaline media
[1, 2]. The applicability field of hydrogen peroxide is
unusually wide because of its being an ecologically
clean oxidizing agent [1, 2].
It is known [3, 11, 12] that hydrogen peroxide s
comparatively easily obtained by cathodic reduction
of oxygen on carbon-graphite electrodes in alkaline
solutions (Berl’s process)
О2 + 2е + Н2О → НО2– + ОН– ,
and in acid solutions by the reaction
О2 + 2Н+ + 2е = Н2О2 .
This method is waste-free and makes it possible
to obtain H2O2 at the consumption site in the form
of aqueous solutions and use these solutions as a
commercial product without preliminary isolation of
H2O2, which substantially diminishes its cost [2, 3, 11,
12].
In the last 20 years, a strong interest has been
expressed in processes for indirect oxidation of organic
and inorganic substances with hydrogen peroxide
electrochemically generated from oxygen under in situ
conditions [3–8]. This is due to the orientation of modern
chemical industries to wide use of principles underlying
conjugated processes [9] involving ecologically clean
reagents, such as electric current and chemically bound
The solubility of oxygen in aqueous electrolyte
solutions is low (approximately 10–3 M), and, therefore,
the process of oxygen electroreduction on smooth
electrodes is limited by the diffusion of the reagent to
the electrode surface. The formation rate of hydrogen
peroxide is comparable with the rate of the competing
reactions and, therefore, the current efficiency by
hydrogen peroxide is not high. Technologically
admissible current densities can be reached by using high
pressures; however, this approach is technically difficult
to be implemented. Therefore, in electrosynthesis of
–
active forms of oxygen (O3, H2O2, HO., HO2 , HO2.,
ROOH) [4, 7]. Based on a number of foreign reports,
researchers come to a conclusion that hydrogen peroxide
is a key reagent for development of high-efficiency
advanced oxidation processes [3, 8, 10]. However,
wider use of hydrogen peroxide in the national economy
is limited by its comparatively high cost in manufacture
by the conventional techniques [2].
68

PILOT LABORATORY ELECTROLYZER
69
hydrogen peroxide, precautions should be taken to
eliminate diffusion limitations by oxygen by developing
the contact area between the electrolyte, electrocatalyst,
and reagent, as, e.g., this is done in bulk electrodes [13–
15]. However, the most promising for this process are
hydrophobized 3D gas-diffusion electrodes [3, 4, 12, 16,
17]. As is known, a highly developed electrocatalyst–
electrolyte–reagent contact surface stable in the course
time is created in electrodes of this kind automatically
because of the capillary equilibrium and there are reliable
channels for delivery of the reagent and electrolyte to
this contact surface at a nearly zero pressure drop [4,
17].
Fig. 1. Schematic of the pilot laboratory electrolyzer with
a gas-diffusion electrode for electrosynthesis of hydrogen
peroxide from oxygen. (1) Gas (oxygen) chamber, (2) cathode
chamber, (3) anode chamber, (4) gas-diffusion electrode, (5)
cation-exchange membrane, (6) methyl methacrylate case of
the electrolyzer, (7) glass coils for cooling of the cathode and
anode chambers, and (8) ORTA anode.
In this communication, we present results of
a preparative electrosynthesis of hydrogen peroxide in
a pilot laboratory three-chamber electrolyzer by cathodic
reduction of oxygen on a two-layer carbon black gas-
diffusion electrode in acid and alkaline electrolyte
solutions.
NaOH + 0.2% Na2SiO3, pH 14. Electrolysis conditions:
total current 7 A; current densities 110 and 50 mA cm–2
for the acid and alkaline electrolytes, respectively;
cathode chamber temperature 27°C. Oxygen (technical
grade) was delivered from a cylinder into the electrode
from its backside under atmospheric pressure.
EXPERIMENTAL
A filter-press electrolyzer, fabricated from methyl
methacrylate, comprised gas, anode, and cathode
chambers. The gas-diffusion electrode (GDE) was
situated between the gas and cathode chambers. The
anode and cathode chambers were separated by an
MK-40 cation-exchange membrane. As the cathode
was used a double-layer hydrophobized electrode
with a thickness of 2–2.2 mm, working surface area
of 64 cm2, and total porosity of 60–65 vol %. A437E
acetylene black with 10–15 wt % fluoroplastic served
as the working layer, and A437E black with 70 wt %
fluoroplastic, as the blocking layer. The mass ratio of the
working and blocking layers was 3 : 10. A stainless steel
wire frame was in the middle of the blocking layer. The
double-layer electrode was fabricated by the method
described in detail in [18]. A ruthenium-titanium anode
(ORTA) was used. The catholyte volume was 0.25 l.
The cathode and anode chambers were cooled by water
flowing through a glass cooling coil. The assembly was
tightened using screw clamps and pins. The electrolyzer
is shown schematically in Fig. 1.
TodeterminethecontentofH2O2 intheelectrolyte,we
thoroughly agitated it with air every hour, took a sample,
and titrated it with potassium permanganate. The results
of electrosynthesis are presented in Figs. 2a and 2b,
which shows the kinetic curve of H2O2 accumulation and
the curve of the corresponding variation of the current
efficiency. It can be seen in Fig. 2a that the experimental
kinetic curve of H2O2 accumulation in the acid catholyte
almost coincides with the run of the curve calculated by
the equation [12, 19]:
(1)
Here, c is the concentration of H2O2 in the catholyte
(M); I, electrolysis current (A); ν, catholyte volume (l);
γ, fraction of current consumed for O2 reduction to H2O2;
τ, electrolysis duration (h); k, rate constant of H2O2
decomposition (h–1); Vd, rate of H2O2 decomposition
(M h–1); and A, electrochemical equivalent of H2O2
(mol A–1 h–1).
The experimental accumulation curves were
used to calculate k and γ by the procedure described
in [19]. The constant k is the overall rate constant of
H2O2 decomposition in the electrolyte bulk and on
the electrolyzer walls and membrane. The current
We performed preparative electrosyntheses of
hydrogen peroxide from oxygen in an acid electrolyte
solution of composition (M): 0.2 H2SO4 + 0.5 K2SO4 +
0.01TBABr (tetrabutylammonium bromide) with pH 1.4
and in an alkaline electrolyte of composition 0.5 M
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 1 2011

70
KOLYAGIN, KORNIENKO
(a)
reactions of oxygen reduction and H2O2 decomposition
[12, 19].
c, M
η, %
О2 + 4Н+ + 4е = 2Н2О ,
О2 + 2Н+ + 2е = Н2О2,
Н2О2 + 2Н+ + 2е = 2Н2О,
2Н2О2 = 2Н2О + О2.
(I)
(II)
60
20
(III)
(IV)
It was found that, in the course of 9 h, the increase in
the concentration of hydrogen peroxide in the catholyte
and the decrease in the current efficiency result in
that the rate of H2O2 accumulation decreases from 2
to 0.9 mmol cm–2 h–1 per unit geometric surface area
of the electrode, or from 0.13 to 0.06 mol h–1 for the
whole electrode. It can be seen in Fig. 2a that, after 9 h
of electrolysis, the concentration of hydrogen peroxide
in solution was 3.0 M and the current efficiency is about
80%.
(b)
c, M
η, %
60
20
It is known that decomposition of hydrogen
peroxide is a rather complex process that depends on
numerous factors [1, 2, 19–21]. The decomposition rate
of hydrogen peroxide in an alkaline medium can be
formally described by various equations:
Vd = kс [19],
(2)
(3)
(4)
τ, h
Vd = kсund + k0 [21],
Vd = kсundсp [22],
Fig. 2. Concentration c and current efficiency by H2O2 (η)
in electrosynthesis from O2 vs. the electrolysis duration τ.
Solution composition (mol g–1): (a) 0.2H2SO4 + 0.5K2SO4 +
0.05TBABr and (b) 0.5NaOH + 0.2% Na2SiO3. Points on
the dependence of concentration, experimental values; line,
calculation by Eq. (1) at (a) k = 0.1 h–1 and γ = 0.99 and (b) k =
0.09 h–1 and γ = 0.93.
where c is the total concentration of H2O2; cund
,
concentration of the undissociated part of H2O2; cp,
–
concentration of peroxide ions (HO2 ); and k and k0,
constants.
efficiency (CE) by H2O2 was calculated from the H2O2
concentration in the catholyte, catholyte volume, and
quantity of passed electricity. The value of γ depends
both on the reaction of H2O2 reduction to water and on
the decomposition rate of hydrogen peroxide within
pores of the electrode to oxygen, which undergoes
repeated reduction [12]. Thus, the value of γ reflects
only process occurring in the electrode, and the current
efficiency is related both to γ and to processes occurring
in the catholyte chamber of the electrolyzer.
However, it can be considered in the presence of
Na2SiO3, a decomposition stabilizer for hydrogen
peroxide, that the decomposition rate is described by
Eq. (2) and the kinetics of H2O2 decomposition is also
described by Eq. (2). This is indicated by the run of the
experimental accumulation curve in Fig. 2b. It can be
seen that electrolysis for 7 h in an alkaline electrolyte
(0.5 M NaOH + 0.2% Na2SiO3) at a current density of
50 mA cm–2 yields a hydrogen peroxide solution with
a density of 11 M and a current efficiency of 86%. In
7 h, the rate of H2O2 accumulation decreases from 0.06
to 0.019 mol h–1. On replacing oxygen with air, the
current efficiency decreases by 30% on average.
It is known that the process of hydrogen peroxide
accumulation in acid electrolytes in electroreduction of
oxygen depends on the relative rates of the following
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PILOT LABORATORY ELECTROLYZER
71
2008.
CONCLUSIONS
7. Ogibin, Yu.N., Elinson, M.N., and Nikishin, G.I., Uspekhi
Khim., 2009, vol. 78, no. 2, pp. 99–150.
The preparative electrosyntheses of hydrogen
peroxide by cathodic reduction of oxygen in a carbon
black double-layer gas-diffusion electrode, performed
in the study, demonstrated that a simple pilot laboratory
three-chamber electrolyzer is highly efficient for
obtaining acid solutions with a concentration of 3 M at
a current efficiency of 75.0% and a current density of
110 mA cm–2 in the course of 9 h and alkaline solutions
with a concentration of 1.1 M at a current efficiency of
86.0% and current density of 50 mA cm–2 in 7 h.
8. Brillas, E., Sires, I., and Oturam, M.A., Chem. Rev., 2009,
vol. 109, pp. 6570–6631.
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ACKNOWLEDGMENTS
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The study was financially supported by the Russian
Foundation for Basic Research-Siberia (grant no. 09-03-
98000).
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