734
M. Ved’ et al.
catalysts can be reduced just to three of them, in particular, a high catalytic activity,
chemical and corrosion resistance, and nontoxicity. Undoubtedly, the activity of
catalysts is defined by the material nature though it depends to a great extent on
the surface condition. It is known that molybdenum compounds possess a certain
catalytic activity with regard to many processes, such as electrochemical methanol
oxidation, the reduction of iodates, oxygen, etc. [15]. Cobalt compounds, in particular, oxides and complexes also found a wide application in the electrocatalysis
[16]. Evidently, it is related to the mobility of oxygen contained by the compounds
of metals, their high coordination capacity, and ability to form nonstoichiometric
oxides [17].
The use of alkaline electrolytes allows us to the extent the range of materials that
can be used for the formation of catalytic matrixes. It is conditioned by the acceleration of the reduction reaction of oxygen, and simple alcohols in alkaline electrolytes
in comparison with acid electrolytes, and a lower corrosiveness of the former with
regard to many transition metals. The problems of the use of methanol as a fuel in
the alkaline environment are related to gradual carbonization of electrolyte when
alcohol is oxidized to CO 2 and the poisoning of precious metal-based electrodes.
Transition metal alloys and manganese oxides turned out to be the efficient catalysts
that reduce the poisoning effect [18, 19]. Hence, detection of the mechanism for the
methanol oxidation on such alloys equally as the maintenance of phasic oxidation
with no formation of carbon dioxide can become a highly promising approach to the
replacement of precious metals by more economic catalytic systems.
Hence, the formation of the layer of electrolytic alloys based on cobalt with
molybdenum (tungsten), and zirconium that has a branched globular surface can
provide a preset route for the methanol electrooxidation process, and increase the
FC operation efficiency using no precious metals. The subject of this paper deals
with the studies of the influence exerted by the qualitative composition of ternary
cobalt alloys with refractory metals on the anodic methanol oxidation rate in alkaline
electrolytes, and it also deals with the analysis of the corrosion resistance of electrode
materials.
1 Experimental
The electrolytic methanol oxidation mechanism, the kinetics, and the corrosion resistance were investigated using the electrodes with the electrolytic coatings of ternary
Co–Mo–W(Zr), Co–Fe–Mo alloys of at least 5μm thick. The Co–Mo–W(Zr) coatings were applied onto the steel substrate from the biligand pyrophosphate–citrate or
citrate electrolytes [9, 20]. The samples were subjected to the preliminary treatment
using the methods given in [21]. The electrodeposition was conducted using the pulse
current at a varied current density, the pulse frequency, and on/off time ratio [9, 20].
The electrolyte temperature at a level of 30–35 ºC was maintained. The Co–Fe–Mo
coatings were deposited onto the steel substrate from the citrate electrolytes based
on the iron (III) by direct (DC) and pulse (PC) current [20].
M. Ved’ et al.
catalysts can be reduced just to three of them, in particular, a high catalytic activity,
chemical and corrosion resistance, and nontoxicity. Undoubtedly, the activity of
catalysts is defined by the material nature though it depends to a great extent on
the surface condition. It is known that molybdenum compounds possess a certain
catalytic activity with regard to many processes, such as electrochemical methanol
oxidation, the reduction of iodates, oxygen, etc. [15]. Cobalt compounds, in particular, oxides and complexes also found a wide application in the electrocatalysis
[16]. Evidently, it is related to the mobility of oxygen contained by the compounds
of metals, their high coordination capacity, and ability to form nonstoichiometric
oxides [17].
The use of alkaline electrolytes allows us to the extent the range of materials that
can be used for the formation of catalytic matrixes. It is conditioned by the acceleration of the reduction reaction of oxygen, and simple alcohols in alkaline electrolytes
in comparison with acid electrolytes, and a lower corrosiveness of the former with
regard to many transition metals. The problems of the use of methanol as a fuel in
the alkaline environment are related to gradual carbonization of electrolyte when
alcohol is oxidized to CO 2 and the poisoning of precious metal-based electrodes.
Transition metal alloys and manganese oxides turned out to be the efficient catalysts
that reduce the poisoning effect [18, 19]. Hence, detection of the mechanism for the
methanol oxidation on such alloys equally as the maintenance of phasic oxidation
with no formation of carbon dioxide can become a highly promising approach to the
replacement of precious metals by more economic catalytic systems.
Hence, the formation of the layer of electrolytic alloys based on cobalt with
molybdenum (tungsten), and zirconium that has a branched globular surface can
provide a preset route for the methanol electrooxidation process, and increase the
FC operation efficiency using no precious metals. The subject of this paper deals
with the studies of the influence exerted by the qualitative composition of ternary
cobalt alloys with refractory metals on the anodic methanol oxidation rate in alkaline
electrolytes, and it also deals with the analysis of the corrosion resistance of electrode
materials.
1 Experimental
The electrolytic methanol oxidation mechanism, the kinetics, and the corrosion resistance were investigated using the electrodes with the electrolytic coatings of ternary
Co–Mo–W(Zr), Co–Fe–Mo alloys of at least 5μm thick. The Co–Mo–W(Zr) coatings were applied onto the steel substrate from the biligand pyrophosphate–citrate or
citrate electrolytes [9, 20]. The samples were subjected to the preliminary treatment
using the methods given in [21]. The electrodeposition was conducted using the pulse
current at a varied current density, the pulse frequency, and on/off time ratio [9, 20].
The electrolyte temperature at a level of 30–35 ºC was maintained. The Co–Fe–Mo
coatings were deposited onto the steel substrate from the citrate electrolytes based
on the iron (III) by direct (DC) and pulse (PC) current [20].