The Electro-Deposition/Dissolution of CuSO₄ Aqueous Electrolyte Investigated by In Situ Soft X-ray Absorption...

The electrodeposition nature of copper on a gold electrode in a 4.8 pH CuSO₄ solution was inquired using X-ray absorption spectroscopy, electrochemical quartz crystal microbalance, and thermal desorption spectroscopy techniques. Our results point out that the electrodeposition of copper prompts the formation of stable oxi-hydroxide species with a formal oxidation state Cu⁺ without the evidence of metallic copper formation (Cu⁰). Moreover, the subsequent anodic polarization of Cu₂O_aq yields the formation of CuO, in the formal oxidation state Cu²⁺, which is dissolved at higher anodic potential. It was found that the dissolution process needs less charge than that required for the electrodeposition indicating a nonreversible process most likely due to concomitant water splitting and formation of protons during the electrodeposition.