Аннотация:In this paper, we study the nucleation and growth of a copper(I) oxide layer during hydrothermaltreatment of copper foil in an alkaline solution. Experimental (X-ray diffraction and scanning electronmicroscopy) data, Gibbs free energy calculations, and analysis of the growth process in terms of the Cabrera–Mott approach lead us to conclude that the hydroxide anion and dissolved oxygen concentrations play a keyrole in determining the phase composition and morphology of the hydrothermal treatment product.