Preparation and electrochemical properties of a novel porous Ti/Sn–Sb-RuOx/β-PbO2/MnO2 anode for zinc electrowinning

Abstract

MnO₂ coatings prepared in a sulfate system (S-MnO₂) and MnO₂ prepared in a nitrate system (N-MnO₂) were successfully deposited on porous Ti/Sn–Sb-RuO_x/β-PbO₂ substrates by electrodeposition, and their electrochemical properties were studied in detail. The bath composition plays a very important role in the MnO₂ coating prepared by electrodeposition at a low current density. The results of scanning electron microscopy show that a Ti/Sn–Sb-RuO_x/β-PbO₂/MnO₂ electrode has a rough morphology and the unit cell is very good. At the same time, the surface cracks in the S-MnO₂ coating are larger than those in the N-MnO₂ coating. In addition, the N-MnO₂ coating is composed of a fluffy sheet-like substance. The surface morphology of the N-MnO₂ coating is denser than that of the S-MnO₂ coating. The S-MnO₂ coating consists of irregularly stacked granular particles. Further, the main crystal phase of MnO₂ is γ type, and the main valence state of MnO₂ is +4. The results show that the oxygen evolution potential of the N-MnO₂ electrode is 63 mV lower than that of the S-MnO₂ electrode, indicating that the N-MnO₂ electrode has better oxygen evolution activity and electrochemical stability, which can also be confirmed by EIS test results. Under the accelerated life test conditions, the N-MnO₂ electrode has a better service life of 77 h at a current density of 1 A cm⁻² in 150 g L⁻¹ H₂SO₄ and 2 g L⁻¹ Cl⁻ solution.