Electrochemical formation and reduction of copper oxide nanostructures in alkaline media

• Cyclic voltammetry of Cu in NaOH solution revealed conversion of nanostructures.
• CuO was reduced from Cu2O nanoparticles in the preferred growth directions.
• Nano branches of CuO dendrites were composed of CuO nanobelts.
• Cu nanoparticles were reduced from Cu2O nanoparticles and residual CuO dendrites.

Formation and reduction of copper oxides in alkaline media were investigated via cyclic voltammetry combined with scanning electron microscopy and focus ion beam. Cu2O nanoparticles were generated in the first oxidation peak of cyclic voltammetry. A layer of CuO dendrite crystal, rooting on copper substrate, was transformed from Cu2O nanoparticles in the preferred growth directions in the second oxidation peak. The nanobranches, composed of nanobelts, and the roots of CuO dendrite crystals were reduced to be Cu2O nanoparticles originating from the roots of CuO dendrite crystal in the first reduction peak during the reverse scan. The reduction of CuO was incomplete at the tail of the first reduction peak. Copper nanoparticles, reduced from Cu2O nanoparticles and the residual CuO dendrite crystals during the second reduction peak, covered the whole sample surface.