8
M. V. Ved’ et al.
The results were verified by mass metric (gravimetric) tests and spectroscopy of
electrode impedance.
Electrocatalytic properties of coatings were studied in model reaction of electrolytic hydrogen evolution from acidic and alkali media. The hydrogen exchange
current density i 0
H is utilized as the criteria of electrochemical catalysis since
this parameter is independent of the electrode potential. Experimentally i 0
H was
determined at the point of intersection, the linear portion of the cathodic polarization
dependence in Tafel coordinates at zero overvoltage [35].
The testing of catalytic properties was also carried out in the process of the
carbon (II) oxide oxidation in a tubular flow reactor fabricated from quartz glass
with the coaxially situated heating element. Initial mixture of CO (1 vol.%) and air
was supplied to the reactor inlet at a rate of 0.025 dm 3 /min. Reactor temperature
was increased gradually from 20 to 420 ◦ C. Content of CO in the final mixture was
analyzed using the indicator-analyzer “Dozor” [36].
1.1.1 FeCoW Alloy
The choice of the quantitative composition of electrolyte is based on accounting
the competing reactions of iron (III) hydrolysis and citrate anion protonation that
determined the ionic equilibrium in the solution and the solution pH. In addition,
peculiarities of the electrochemical behavior of the electrolyte components were
taken into account [32]. Increasing the concentration of citrate ions in solution
at fixed Fe 3+ content expectedly increases the electrolyte pH (Table 1.1). The
protonation of citrate anions decreases with pH, while the degree of Fe 3+ hydrolysis
increases; therefore ionic forms of complexing agents and ligand in the electrolytes
are different. Consequently, the composition of particles discharged at the electrode
varies, which effects the composition of coatings.
Fe-Co-Mo alloy deposition occurs by competitive reduction of iron, cobalt,
and tungsten. The form of competition depends on the ratio of electrolyte components and electrolysis parameters (Fig. 1.1). We observe a slight decrease
in the cobalt content without changing the iron portion in the alloy at current
densities of 2.0−3.0 A/dm 2 when components’ concentration ratio in the electrolyte
Ô(Fe 3+ ):Ô(´Ñ 2+ ):Ô(WO 4
2− ):Ô(Cit 3− ) is 1:1:0.4:2 (Fig. 1.1a). Coatings are enriched
with cobalt at the expense of iron if increasing i Ô up to 4 A/dm 2 , but higher current
density contributes cobalt content decreasing to 40 at.%. The tungsten content in the
deposits increases with current density, but does not exceed to 8 at.%.
Changing the ratio of alloying component content in the electrolyte in favor of
cobalt with the simultaneous increase of the ligand concentration up to 0.4 mol/dm 3
(electrolyte Mo2, Table 1.1) leads to an inversion of the metal ratio in the alloy
(Fig. 1.1b). This occurs as a result of a change in the composition of heteronuclear complexes discharged at the electrode. The cobalt content exceeds the
iron portion in coatings deposited at current densities of 3−7 A/dm 2 . A trend to
gradually decreasing the cobalt content is observed with increasing current density
M. V. Ved’ et al.
The results were verified by mass metric (gravimetric) tests and spectroscopy of
electrode impedance.
Electrocatalytic properties of coatings were studied in model reaction of electrolytic hydrogen evolution from acidic and alkali media. The hydrogen exchange
current density i 0
H is utilized as the criteria of electrochemical catalysis since
this parameter is independent of the electrode potential. Experimentally i 0
H was
determined at the point of intersection, the linear portion of the cathodic polarization
dependence in Tafel coordinates at zero overvoltage [35].
The testing of catalytic properties was also carried out in the process of the
carbon (II) oxide oxidation in a tubular flow reactor fabricated from quartz glass
with the coaxially situated heating element. Initial mixture of CO (1 vol.%) and air
was supplied to the reactor inlet at a rate of 0.025 dm 3 /min. Reactor temperature
was increased gradually from 20 to 420 ◦ C. Content of CO in the final mixture was
analyzed using the indicator-analyzer “Dozor” [36].
1.1.1 FeCoW Alloy
The choice of the quantitative composition of electrolyte is based on accounting
the competing reactions of iron (III) hydrolysis and citrate anion protonation that
determined the ionic equilibrium in the solution and the solution pH. In addition,
peculiarities of the electrochemical behavior of the electrolyte components were
taken into account [32]. Increasing the concentration of citrate ions in solution
at fixed Fe 3+ content expectedly increases the electrolyte pH (Table 1.1). The
protonation of citrate anions decreases with pH, while the degree of Fe 3+ hydrolysis
increases; therefore ionic forms of complexing agents and ligand in the electrolytes
are different. Consequently, the composition of particles discharged at the electrode
varies, which effects the composition of coatings.
Fe-Co-Mo alloy deposition occurs by competitive reduction of iron, cobalt,
and tungsten. The form of competition depends on the ratio of electrolyte components and electrolysis parameters (Fig. 1.1). We observe a slight decrease
in the cobalt content without changing the iron portion in the alloy at current
densities of 2.0−3.0 A/dm 2 when components’ concentration ratio in the electrolyte
Ô(Fe 3+ ):Ô(´Ñ 2+ ):Ô(WO 4
2− ):Ô(Cit 3− ) is 1:1:0.4:2 (Fig. 1.1a). Coatings are enriched
with cobalt at the expense of iron if increasing i Ô up to 4 A/dm 2 , but higher current
density contributes cobalt content decreasing to 40 at.%. The tungsten content in the
deposits increases with current density, but does not exceed to 8 at.%.
Changing the ratio of alloying component content in the electrolyte in favor of
cobalt with the simultaneous increase of the ligand concentration up to 0.4 mol/dm 3
(electrolyte Mo2, Table 1.1) leads to an inversion of the metal ratio in the alloy
(Fig. 1.1b). This occurs as a result of a change in the composition of heteronuclear complexes discharged at the electrode. The cobalt content exceeds the
iron portion in coatings deposited at current densities of 3−7 A/dm 2 . A trend to
gradually decreasing the cobalt content is observed with increasing current density