Nanostructured Electrolytic Composites Based on Cobalt Alloys …
737
formation of the oxides of a variable composition on the alloy surface during the
anode polarization:
(MO x−1 ) S + 2OH
−
→ (MO x ) S + H 2 O + 2e,
(5)
oxygen in them is mobile and can be transferred to the carbon atom without additional
energy inputs as in the case of the participation of hydroxide ions in the reaction (3).
Subsequent transitions in the system are related to the formation of the water
molecule and intermediate carbon oxide (II) according to the chemical reaction:
(HCOOH) S → (CO) S + H 2 O,
(6)
and a further (CO) S → CO 2 transformation is of no interest for the functioning of
fuel cells, and this link can be excluded from the general scheme if potential varying
intervals will be limited.
Hence, the investigation of the process of methanol oxidation on the alloys of
cobalt with molybdenum and tungsten (zirconium) is the foundation for the formation
of efficient catalysts for FC.
3 Results and Discussion
The coatings formed by ternary Co–Mo–W alloys are characterized by the uniformly
branched globular surface (Table 1, specimens 1, 2) whose relief differs considerably
from that of the substrate onto which these are applied (Fig. 1a, b).
We can see the cracks and a number of pores on the surface of specimen 2 (Table 1)
which is coated with Co–Mo–W at the current density 6 A/dm
2 . Such a phenomenon
is associated with two reasons. Firstly, a higher rate of nucleation and growth of crystallites at a higher current density leads to an increase in internal stresses in coatings
and following cracking. Secondly, the hydrogen evolution reaction is intensified with
increasing polarization and causes the porosity of the coating.
The analysis of ACM data is indicative of the nanoglobular character of the surface
of Co–Mo–W coatings on which the cone-shaped associates with the diameter of
2–5 μm are formed due to the merging of fine globules with a diameter of 20–80 nm.
The roughness parameters calculated for the section area of 20 × 20 μm are: R a =
0.02 and R q = 0.04.
Ternary coatings with Co–Mo–Zr alloy differ from Co–Mo–W ones by a more
branched surface, and uniformly distributed cone-shaped associates with a diameter
of 5–7 μm (Fig. 1c, d). The cobalt content increases with the current density and an
extension of the pulse time. However, the percentage of alloying metals is decreased
in comparison with that of Co–Mo–W coatings (Table 1, specimens 3–5). Despite
this, the origination of cracks in Co–Mo–Zr coatings is independent of the content of
refractory components as well as of current density. Many studies have paid attention
to the cracking of binary and ternary cobalt and molybdenum alloys [28, 29]. A
737
formation of the oxides of a variable composition on the alloy surface during the
anode polarization:
(MO x−1 ) S + 2OH
−
→ (MO x ) S + H 2 O + 2e,
(5)
oxygen in them is mobile and can be transferred to the carbon atom without additional
energy inputs as in the case of the participation of hydroxide ions in the reaction (3).
Subsequent transitions in the system are related to the formation of the water
molecule and intermediate carbon oxide (II) according to the chemical reaction:
(HCOOH) S → (CO) S + H 2 O,
(6)
and a further (CO) S → CO 2 transformation is of no interest for the functioning of
fuel cells, and this link can be excluded from the general scheme if potential varying
intervals will be limited.
Hence, the investigation of the process of methanol oxidation on the alloys of
cobalt with molybdenum and tungsten (zirconium) is the foundation for the formation
of efficient catalysts for FC.
3 Results and Discussion
The coatings formed by ternary Co–Mo–W alloys are characterized by the uniformly
branched globular surface (Table 1, specimens 1, 2) whose relief differs considerably
from that of the substrate onto which these are applied (Fig. 1a, b).
We can see the cracks and a number of pores on the surface of specimen 2 (Table 1)
which is coated with Co–Mo–W at the current density 6 A/dm
2 . Such a phenomenon
is associated with two reasons. Firstly, a higher rate of nucleation and growth of crystallites at a higher current density leads to an increase in internal stresses in coatings
and following cracking. Secondly, the hydrogen evolution reaction is intensified with
increasing polarization and causes the porosity of the coating.
The analysis of ACM data is indicative of the nanoglobular character of the surface
of Co–Mo–W coatings on which the cone-shaped associates with the diameter of
2–5 μm are formed due to the merging of fine globules with a diameter of 20–80 nm.
The roughness parameters calculated for the section area of 20 × 20 μm are: R a =
0.02 and R q = 0.04.
Ternary coatings with Co–Mo–Zr alloy differ from Co–Mo–W ones by a more
branched surface, and uniformly distributed cone-shaped associates with a diameter
of 5–7 μm (Fig. 1c, d). The cobalt content increases with the current density and an
extension of the pulse time. However, the percentage of alloying metals is decreased
in comparison with that of Co–Mo–W coatings (Table 1, specimens 3–5). Despite
this, the origination of cracks in Co–Mo–Zr coatings is independent of the content of
refractory components as well as of current density. Many studies have paid attention
to the cracking of binary and ternary cobalt and molybdenum alloys [28, 29]. A