1966
PIRSKII et al.
Complex (I) is more thermally stable. Its destruc-
tion also begins with decomposition of the ligand L
in the range 130 320 C (15.1%). The decomposition
products are similar for complexes I III (Fig. 1b). In
the range 320 710 C, the decomposition of the ligand
L is complete (43.1%) to give pyrolysis products in
the form of a mixture Ni + ZnCl2.
The substances obtained were analyzed in the reac-
tion of electrochemical reduction of oxygen in a three-
electrode electrochemical cell (with 1 M KOH solu-
tion and separated cathode and anode spaces) by
the method of the floating gas-diffusion electrode
[9] at 20 C. The floating gas-diffusion electrode had
the form of a pellet of hydrophobized acetylene black
containing 30 wt % polytetrafluoroethylene, with
Fig. 2. Rate of oxygen electroreduction on catalysts formed
by pyrolysis of heterobimetallic complexes on AG-3 in
a 1 M KOH solution at 20 C vs. the pyrolysis temperature
T. ( j) Current density. Potential E = 0.1 V relative to
3
a mass of 300 mg, density of 0.95 g cm , diameter
of 10 mm, and thickness of 2 mm, compacted under
a pressure of 5 7 MPa. A nickel-wire current lead was
embedded in the pellet. A layer of an electrocatalyst
under study, with a particle size of less than 20 m,
Ag/AgCl reference electrode. Complex: (1) [CuL][ZnCl ],
4
(2) [NiL][ZnCl ], and (3) [CoL][ZnDMFACl ].
4
3
2
tra are rather intricate, Fig. 1 shows for all the com-
plexes only selected data for species with m/z less
than 29. The mass-spectra clearly show the temper-
ature ranges in which the intensity of pyrolysis of
the complexes under study is the highest. At 180
220 C occurs partial decomposition of the ligand
(4,6,6-trimethyl-1,9-diamino-3,7-diaza-nona-3-ene)
and the thermogravimetric curve demonstrates a con-
siderable loss of mass (12.2%). The mass spectra
reveal splitting-off of the following species: NH+4,
NH3, CH+3, CH NH2+, CH NH+, CH2 CH+2, etc.
Some of the species desorbed add a Cl ion to form
species with m/z exceeding 36. Molecular Cl2 formed
in pyrolysis may be present in decomposition prod-
ucts in minor amounts, with m/z of 69, 70, 71. In
the following stage of pyrolysis (220 280 C) con-
tinues decomposition of the ligand and zinc oxide
starts to be formed. In the range 280 620 C occurs
full decomposition of the organic ligand to give the
final product in the form of a mixture CoCl2 + ZnO,
which is confirmed by the results of elemental and
thermal analyses.
was deposited in an amount of 1 mg cm onto the
electrode surface and compacted under a pressure of
5 6 MPa. This amount of the catalyst provided a ki-
netic mode of the electrochemical reaction [10].
The catalyst was retained on the surface of the support
by adhesion forces. Polarization curves were measured
in the potentiostatic mode on a PI-50-1.1 potentiostat
with a step of 10 mV. The current was recorded with
an M 2020 milliammeter.
The activity was evaluated by the current of ox-
ygen reduction, observed at a potential of 0.10 V,
and by the slope of the polarization curve, E/ log j
(b1; b2). The kinetic characteristics of oxygen electro-
reduction on the catalyst, obtained in the study, are
listed in the table. Dependences of the rate of oxygen
electroreduction at a constant potential E = 0.1 V
on the temperature at which the electrocatalysts based
on heterobimetallic complexes were synthesized are
shown in Fig. 2. It can be seen from Fig. 2 and
the table that the highest current of oxygen reduction
is observed for the catalysts obtained from heterobi-
metallic complexes of copper and zinc at 700 C. It
is known that electrocatalysts produced from por-
phyrin and phthalocyanine complexes [5, 11, 12] at
The thermolysis of complex (III) begins with de-
composition of 4,6,6-trimethyl-1,9-diamino-3,7-diaza-
nona-3-ene. In the temperature range 100 240 C,
the mass spectrometer records (Fig. 1c) such desorp-
tion products as NH+4, NH3, CH3+, CH NH+2, CH NH+,
CH2 CH+2 and chlorine-containing species with
heavier mass (loss of mass was 15.1% of the total
mass of the complex). At 240 550 C, the decomposi-
tion of the organic ligand is complete (37.6%) to give
pyrolysis products containing ZnCl2 and fragments of
a compound of copper and nitrogen.
T
800 C form active centers in which the MN4
structure is preserved, and its chemical bonding with
the carbon support is assumed.
Thus, 700 800 C is the optimal temperature range
for production of active catalysts from complexes
based on copper zinc heterobimetallic complexes,
which decompose in an inert atmosphere on the carbon
surface and, probably, also form metal-and-nitrogen-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 12 2006