Anodic dissolution phenomena accompanying supersaturation of copper sulfate along a vertical plane copper anode

Vertical plane copper anode was electrochemically dissolved in a stagnant CuSO₄ and CuSO₄-H₂SO₄ electrolyte solution. Measured anodic polarization curve showed three distinct stages: Stage I characterized by an increased current density with increasing in anodic overpotential, Stage II including a maximum peak current followed by an abrupt current decrease caused by CuSO₄ precipitates at higher overpotential and Stage III with much lower and virtually constant current density, that is, the existence of anodic limiting current density over a wide anodic overpotential range. The complete passivation phenomena were not encountered in the present experimental conditions. Supersaturation phenomena of Cu²⁺ near the anode surface in Stage II were in-situ measured by holographic interferometry. The degree of supersaturation more than 0.18 M CuSO₄ was recorded. It was followed by the nucleation phenomena of a kind of CuSO₄ crystal after a certain incubation period. With growth of precipitates on the anode, the degree of supersaturation of Cu²⁺ ion around them slightly decreased. A similar phenomenon was also observed in CuSO₄-H₂SO₄ solution. The measured anodic limiting current density in Stage III agreed well with the calculated one from the correlation equation: