Direct Observation of Pure Cu and Cu-Ag Anode Passivation in H2SO4-CuSO4 Aqueous Solution by Channel Flow Double Electrode and Optical Microscopy
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The dissolution and passivation of pure Cu and Cu-5 wt pct Ag anodes in H2SO4-CuSO4 electrolyte were investigated by a direct observation method that combined the techniques of optical microscopy and channel flow double electrode. Linear sweep voltammetry of the anodes showed that the dissolution of Cu transited from the charge transfer-controlled reaction to the mass transfer-controlled reaction, followed by the passivation of the electrodes. The direct observation of the pure Cu anode revealed that Cu particles were generated on the surface and the particles fell away during passivation. On the other hand, a slime layer of Ag particles that adhered to the surface was generated during the dissolution of the Cu-5 wt pct Ag anode. The Cu-5 wt pct Ag anode was passivated with a lower current density than the pure Cu anode, which suggested that the morphology and adhesive characteristics of the slime on the anode affected the passivation. The direct observation method described herein is useful for understanding reactions on electrodes that undergo drastic changes in their surface morphology. Information obtained from this method can help with the development of new processes for the effective utilization of limited natural resources and energy, such as the recycling of Cu by electrorefining.
We would like to express our gratitude to Professor T. H. Okabe (Institute of Industrial Science, The University of Tokyo) for his advice on composing the manuscript and Mr. H. Kimura (The University of Tokyo) for technical assistance with the experiments. This study is a part of a research project by the Agency for Natural Resources and Energy. The authors are grateful for the financial support and advice on our experimental design from the Japan Oil, Gas and Metals National Corporation (JOGMEC).
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