The effect of applying sandblasting during pretreatment while preparing titanium based IrO2−Ta2O5 anodes by the conventional method was investigated. It was observed that sandblasting influences the ...surface morphology both before and after coating as deeper and smaller etching pits are obtained on the substrate before coating process and rougher surface is obtained after coating. As a result larger outer electrochemical active surface area (ECSA) is obtained on the anodes with sandblasting, which was determined based on cyclic voltammetry, whereas the inner ECSA is independent of the pretreatment. The polarization measurements in a quasi-steady state reveal that sandblasting has slight influence on the catalytic activity. Accelerated lifetime tests were carried out in acidic 0.9 mol L−1 Na2SO4 solution (pH = 2) at a current density of 5 × 107 A cm−2 under galvanostatic conditions. It shows that sandblasting would shorten the lifetime of the anode due to oxidation of the titanium substrate. This is suggested to be due to the shorter distance between the lowest spot of the outer coating surface and the highest spot of the outer substrate of the anode after applying sandblasting in titanium substrate pretreatment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, industrial IrO2-Ta2O5 anodes calcined at different temperatures were investigated. The results show that the calcination temperature has significant influence on the surface ...microstructure including the crystallinity and the preferred orientation of IrO2 crystallite of the formed IrO2-Ta2O5 binary oxide. The IrO2 phase is partially amorphous at low calcination temperature in the present study. The (101) IrO2 planes dominates at low or moderate calcination temperatures, whereas the (110) IrO2 orientation was preferred at the highest calcination temperature. Surface morphology of the anodes was revealed as mud-cracks surrounded by a flat area with plenty of scattered nano-IrO2 crystallites. The size of the nano-IrO2 crystallites is calcination temperature dependent, which in turn determines the electrochemical active surface area (ECSA). In this IrO2-Ta2O5 binary oxides coating, (101) IrO2 was found to have higher catalytic activity than (110) IrO2 with respect to the oxygen evolution reaction (OER). The moderate temperature is suggested as the best calcination temperature for this certain anode regarding the ECSA, electrocatalytic activity for OER and stability potential.
Nickel may be produced in acidic chloride-sulfate based electrolytes. Nickel is initially deposited on stainless steel or titanium cathodes to produce starting sheets while chlorine gas is evolved on ...DSA anodes. Stress in the nickel deposit may cause bending of the cathode sheet. In addition, irregular growth such as dendrite formation may occur. In extreme cases, short-circuiting of electrodes will happen. Fundamental electrochemical studies of the initial stages of the electrodeposition process may give valuable information for obtaining smooth nickel deposits.
Electrochemical experiments of nickel deposition were carried out on titanium substrates using cyclic voltammetry and potential step, and examined with SEM imaging. The measurements were performed at different deposition potentials and times to get an overall picture of the nucleation and growth of nickel on titanium substrates. Further deposition studies have been performed using
in situ
AFM to study the whole process from single nickel nuclei to a cohesive layer, and determine the nucleation mode and characteristics. The effects of electrolyte composition and pH will be presented.
The pre-treatment of the substrate is important for the nucleation and properties of the nickel deposit. The figure illustrates the different nucleation overpotential for a smooth and rough titanium substrate.
Figure 1
Nickel may be produced by electrolysis in acidic chloride based electrolytes. Nickel is initially deposited on stainless steel or titanium starting sheets while chlorine gas is evolved on DSA anodes. ...Stress in the nickel deposit may cause bending of the cathode sheet. Also irregular growth such as dendrite formation may occur. In extreme cases short circuiting of electrodes will happen. Fundamental electrochemical studies of the initial stages of the electrodeposition process may give valuable information for obtaining smooth nickel deposits.
Initial experiments were carried out by using cyclic voltammetry on cathodes of titanium. Ongoing studies are performed by potential step chronoamperometry to study the nucleation and growth of nickel on titanium cathode substrates. Experiments to study the effect of electrolyte composition, pH and temperature on the nickel deposition process are under way. Electrolysis to deposit macroscopic amounts of nickel will be carried out to characterize the deposits by optical methods.
Lead-based anodes are widely used in copper electrowinning (EW). However, lead can induce contamination of the electrolyte during copper EW due to the corrosion of the anode 1. Furthermore, corrosion ...while at high current densities will finally lead to the failure of the anode since the overvoltage for oxygen evolution reaction (OER) on lead is still rather high, and the service life of lead-based anodes is quite limited in industrial copper plants 2. Besides, lead and lead compounds are toxic, which means the use of lead-based anodes is not environmentally friendly. Dimensionally stable anodes (DSAs) with IrO
2
-Ta
2
O
5
oxides coated on titanium substrates hold excellent electrocatalytic activity and electrochemical stability, and have the most potential to replace lead-based anode in copper EW industry.
In this work, different types of commercially available electrode samples with IrO
2
-Ta
2
O
5
coating were studied. The studies focused on investigating the impact of surface microstructure on electrocatalytic activity. Surface morphology and chemical composition of DSA samples were analyzed using scanning electron microscopy (SEM, Hitachi S-3400N) combined with energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) studies were carried out using Bruker AXS D8Advance with grazing incident angle at 3°. The crystalline structure and phase composition were analyzed by varying the 2θ angle from 10° to 80°. The electrochemical experiments were carried out in aqueous solution with 0.9 M H
2
SO
4
and 1.2 M CuSO
4
. A Teflon holder giving a 1 cm
2
electrode surface area was used. All experiments were conducted at 60 °C. Cyclic voltammetry (CV) measurements were recorded in a range between 0.55 V and 1.35 V vs. SHE with varying sweep rate from 300 mV/s to 1 mV/s. The scan rate for all polarization measurement was 0.5 mV/s. The ohmic (IR) drop during the testing was corrected for by measuring the electrolyte resistance using electrochemical impedance spectroscopy (EIS) at high frequency. Electrocatalytic activity for anodes as a function of composition and preparation method was determined by steady state polarization analysis. The durability of the anodes was investigated by accelerated lifetime tests, which were carried out in 0.9 M H
2
SO
4
solution at the constant current density of 2 A/cm
2
.
In the present work, commercial DSAs were used instead of samples fabricated in the laboratory. This offers not only valuable results for DSAs research but also a consideration for DSAs manufacturers to improve the quality of the DSA.
1 M. Clancy, C. J. Bettles, A. Stuart, N. Birbilis, Corrosion behaviour and catalytic effectiveness of Pb–Ca–Sn, RuO
2
–IrO
2
/Ti and IrO
2
–Ta
2
O
5
/Ti anodes for copper electrowinning, Hydrometallurgy 131-132 (2013) 144.
2 G. N. Martelli, R. Ornelas, G. Faita, Deactivation mechanisms of oxygen evolving anodes at high current densities, Electrochim. Acta 39 (1994) 1551.
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