Exploiting Cu(II) Amphoterism for the Epitaxial Electrodeposition of Cuprous Oxide and Copper on Gold(111) from an Alkaline Bath Free of Organic Complexing Agents

Epitaxial Cu2O and epitaxial Cu are usually accessed from chemically distinct electrodeposition baths. Here, we show that both can be obtained from a single alkaline Cu(II) electrolyte without added organic complexing ligands by exploiting Cu(II) amphoterism in 3 M NaOH. Speciation and solubility calculations show that a 5 mM Cu(II)/3 M NaOH bath can support dissolved Cu(II) and that Cu(OH)42– is the dominant dissolved mononuclear Cu(II) species. Voltammetry identifies distinct cathodic regimes for Cu2O deposition, Cu deposition, and reduction of pre-existing Cu2O films: deposition at −0.35 V vs Ag/AgCl yields Cu2O, whereas deposition at −0.80 V vs Ag/AgCl yields Cu, and film reduction occurs at −1.1 V vs Ag/AgCl. Hydrodynamic voltammetry shows that Cu deposition is strongly mass-transport dependent, whereas Cu2O deposition is only weakly dependent on rotation rate, indicating different transport and interfacial constraints in the two regimes. X-ray diffraction shows that the Cu2O regime yields single-domain epitaxial Cu2O(111) on Au(111), whereas the Cu regime yields epitaxial Cu(111) with twin in-plane domains. Switching the applied potential further enables sequential epitaxial Cu/Cu2O bilayer growth while retaining the Cu2O underlayer. These results establish a chemically simple route to potential-programmed epitaxial oxide/metal growth from a single alkaline Cu(II) electrolyte.