Effect of iridium(IV) ions on the electrowinning of zinc from acidic electrolytes

The effect of Ir(IV) ions on the electrowinning of zinc from acid sulfate electrolytes was studied using scanning electron microscopy and electrochemical measurements. The change in the surface morphology of the deposits, cathodic current efficiency, polarization behavior, and cathodic potential were investigated. The results showed that Ir(IV) ions in the electrolyte co-deposited with zinc on the cathode and significantly reduced the hydrogen overpotential from − 1.022 V to − 0.99 V vs. saturated calomel electrode (SCE). The cathodic current efficiency decreased from 85% to less than 3% when the Ir(IV) ion concentration was 2.0 mg dm− 3. The presence of Ir(IV) ions also affected the surface macro- and microstructure of the zinc deposits. In the presence of Ir(IV) ions, a large number of circular holes were found on the surface of the zinc deposits. This result confirmed that Ir(IV) ions have a significant negative influence on the electrowinning of zinc.