Quantity of evolved hydrogen

Dish-like holes were formed from the more concentrated solution (0.60 MCUSO4 in 0.50 M H2SO4), accompanied by a considerably lower quantity of evolved hydrogen (jjav(I h) = 4.6%) than was the case with the holes forming a honeycomb-like structure (0.075 M and 0.15 M Q1SO4 in 0.50 M H2S04). 

Finally, the analysis of the break-off diameter (or the diameter of the detached hydrogen bubble) can give an explanation why the change of hydrodynamic conditions in the near-electrode layer is achieved from the copper solution with the lower quantity of evolved hydrogen (i.e. from 0.15 M Q1SO4 in 0.50M H2SO4 at 800 mV... 

The number of craters or holes forming the honeycomb-like structure increased rapidly with the quantity of evolved hydrogen, as can be seen from Fig. 42 which shows the dependence of the number of holes or craters formed due to the attachment of hydrogen bubbles on the average current efficiency of hydrogen evolution. 

VI. THE SHAPE OF ELECTROCHEMICALLY FORMED COPPER POWDER PARTICLES AND THEIR DEPENDENCE ON THE QUANTITY OF EVOLVED HYDROGEN... 

Nikolic ND, Brankovic G, Pavlovic MG, Popov KI (2008) The effect of hydrogen codeposition on the morphology of copper electrodeposits II. Correlation between the properties of electrolytic solutions and the quantity of evolved hydrogen. J Electroanal Chem 621 13-21... 

Figure 5.10 shows the honeycomb-like structures obtained by the PO regimes with an overpotential amplitude of 1000 mV, pause duration of 10 ms, and deposition pulses of 3 ms (Fig. 5.10a), 5 ms (Fig. 5.10b), and 20 ms (Fig. 5.10c). The quantities of evolved hydrogen spent for formation of these electrodes corresponded to the average current efficiencies of hydrogen evolution, //i,av(H2) of 16.4, 22.4, and 28.1 %, respectively [49]. As a reminder, the honeycomb-like electrode was obtained at the constant overpotential equal to this overpotential amplitude with //i,av(H2) of 30.0 % [4, 5, 23]. Analysis of the honeycomb-like...

From the above consideration, it is clear that the maximal surface area of the honeycomb-like electrodes can be attained by the careful selection of parameters of the PO regimes. This is followed by the decrease in the quantity of evolved hydrogen and, hence, by the improvement of the structural stability of the honeycomb-like electrodes. Simultaneously, analysis of the specific energy consumption shows that energy saving is achieved in the production of the honeycomblike electrodes by the shortening of deposition pulse and by the decrease in the quantity of evolved hydrogen [23, 49]. 

Figure 5.11 shows Cu deposits obtained with the current density amplitudes of 0.20 A cm (Fig. 5.11a) and 0.44 A cm (Fig. 5.11b). In both cases, a deposition pulse of 1 ms and a pause duration of 10 ms were applied [22,23,55,57]. Formation of these deposits was accompanied by the quantity of evolved hydrogen which corresponded to the average current efficiency of hydrogen evolution, /i,av(H2), of 5.5 % with the applied current density amplitude, ic, of 0.20 A cm [57], and...

Figure 5.13 shows the honeycomb-like electrodes obtained by the RC and DC regimes. The selected average current density in the RC and the current density in the DC regimes were 0.12 A cm . Both honeycomb-like electrodes were obtained with the approximately same quantity of evolved hydrogen which corresponded to 7i,av(H2) of 22.0 0.8 % [23, 52], It was understandable because both electrodeposition processes occurred at the same current density. 

Of course, hydrogen evolution affects mechanism of formation of powder particles. The dendrites are formed without, as weU as with, a quantity of evolved hydrogen (the case of Cu) which was insufficient to achieve any effect on the hydrodynamic conditions in the near-electrode layer. Then, the electrodeposition process was primarily controlled by the diffusion of ions to the electrode surface, rather than the kinetic of the electrodeposition [5,6], The cauUflower-Uke particles are formed in the conditions of vigorous hychogen evoluticMi with the strong effect of evolved hydrogen on the hydrodynamic conditions in the near-electrode layer, and the concept of effective overpotential is proposed to explain formation of these particles [25, 35]. 

Due to the ionic equilibrium of the species in the CUSO4-H2SO4-H2O system (Fig. 3.2), the quantities of evolved hydrogen and hence morphologies of powdered copper deposits depend strongly on the... 

Correlation Between Morphology of Powder Particles Obtained by the Different Regimes of Electrolysis and the Quantity of Evolved Hydrogen... 

In the dependence of the quantity of evolved hydrogen, the two types of powdered deposits are formed [32, 54]. The typical powdered deposits electrodeposited from 0.075 M CUSO4 in 0.50 M H2SO4 at an overpotential of 650 mV (plateau of the limiting diffusion current density) and at an overpotential of 1,000 mV (about 250 mV above the plateau) are shown in Fig. 3.7a, b, respectively. 

In the dependence of concentration of Cu(II) ions, and hence the quantity of evolved hydrogen, the comcob-like elements can be grouped the different forms of dendritic particles from tree-like to those formed as flowers (Fig. 3.9a, b) or alternatively can be formed individually at the electrode surface (Fig. 3.9c) [31]. 

The fact that morphology of electrodeposited copper is determined by the difference between the overall quantity of evolved hydrogen and those spent for the creating of holes can be confirmed by the following consideration. 

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