The effect of the parameters of the two-pulse electrolysis on the process of electrodeposition of porous nickel dendritic deposits was investigated from the electrolyte, g/l: NiSO4•7H2O - 57.4; NaCl - 200; NH4Cl - 50, pH = 4.8. Cathodic polarization curve was obtained (Fig. 1) in order to determine the parameters of the electrolysis, and studies were carried out using the method of chronopotentiometry at constant current. Current of odd pulses (idep), during which the dendritic deposit was formed, exceeded the limiting current by 2.5-3.5 times, and the current of even pulses (ifix) for fixing the deposit was 2 times smaller than the limit current. The time of the dendritic electrodeposition pulses was longer than the transition time. The potential’s shift to the positive values with increasing number of pulses (Fig. 2) indicates that the real current density in the electrolysis process becomes smaller due to surface development, but remains high enough for the emergence of new dendrites. Nickel deposition under kinetic control during even pulses contributed to the fixation of dendrites on the substrate surface. Porous nickel deposits strongly bonded to the base were obtained in the pulse modes idep/ifix= 500/100; 600/100 and 700/100 A/m2, at the time of the deposition pulse tdep = 5-6 s and the time of the dendrite fixation pulse tfix = 3 s (Fig. 3). Surface areas of nickel dendritic deposits were determined (Table 1) using the method of impedance spectroscopy. The current value and pulse duration have a significant effect on the surface size and deposits properties. The overvoltage of hydrogen and oxygen evolution processes on samples with nickel dendritic deposits was estimated by the cathodic and anodic polarization curves (Fig. 6) in a solution of 6 M KOH. Sections of polarization curves in the area of currents close to the industrial conditions are shown in semi-logarithmic coordinates in Fig. 6 A, B. The results obtained showed that at the current density of 3000 A/m2, the overvoltage of hydrogen evolution on nickel electrodes with a dendritic surface is 190-330 mV smaller, and oxygen evolution is 170-280 mV smaller than that on a smooth nickel. It is suggested that the lack of correlation between the surface area of dendritic deposits and the reduction of cathodic and anodic overvoltage is due to the fact that a higher thickness of the dendritic layer, the structure of the porous layer and the shielding of the surface by gas bubbles starts to play an important role.
|Translated title of the contribution||FORMATION NICKEL DEPOSITS WITH LARGE THRU SURFACE AREA BY PULSING ELECTRODEPOSITION|
|Number of pages||10|
|Journal||Гальванотехника и обработка поверхности|
|Publication status||Published - 2020|
Level of Research Output
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