Thermoelectrochemical Synthesis of Nanostructured Cupric Oxide (CuO) Using KMnO₄ as an Oxidant

This research focuses on combining hydrothermal (hot water treatment) and electrochemical synthesis (EC) forming an advanced method termed ″thermoelectrochemical (TEC)" that introduces a rapid and controllable electrochemical strategy for synthesizing cupric oxide (CuO) nanostructures using potassium permanganate (KMnO₄) as an oxidant under a constant electric potential at 75 °C for 3 h. The influence of applied voltage polarity on phase evolution, oxidation state, and morphology was systematically investigated. Under a positive bias of +Δ5 V, the copper substrate was fully oxidized into stoichiometric CuO, as confirmed by sharp XRD reflections, Raman-active Cu-O modes, and EDS spectra dominated by Cu-O composition. The average crystallite size was estimated to be 10.3 ± 0.5 nm, confirming the formation of nanocrystalline CuO. In contrast, applying a negative bias of -Δ5 V produced a mixed phase of nanorods and nanocubes, accompanied by the emergence of copper manganite (CuMn₂O₄), evidenced by the characteristic XRD peak at 40.6° and supported by EDS analysis, alongside residual Mn and Cu phases. In the absence of an applied electric potential (Δ0 V), KMnO₄-only as an oxidant led to incomplete copper oxidation, highlighting the crucial role of electric field polarity, while the positive bias dissolved and full conversion occurred to black CuO powder nanostructures. Notably, the XRD peak at 44.6° observed in all samples confirms the presence of paramelaconite (Cu₄O₃). Importantly, the +Δ5 V condition favors copper oxide powder with a high surface area, making it suitable for catalysis and highly reactive applications, whereas the -Δ5 V condition and (Δ0 V) KMnO₄-only oxidation favor adherent copper oxide films that are advantageous for electronics, optics, and device integration. This integrated approach combining redox chemistry, thermal energy, and electrochemical control offers a scalable and time-efficient route for synthesizing CuO, Cu₄O₃, and CuMn₂O₄ nanostructures, and it is currently being investigated for extension to other metal oxides.