Heterostructured MnO ₂ /CuO on Cu Wire for Electrochemical Energy Storage: Insights from Spectro‐Microscopy

Abstract A fundamental understanding of charge storage mechanisms in bimetallic oxide heterostructures remains a key challenge in electrochemical energy storage research. In the present work, the heterostructures of manganese oxide/copper oxide (MnO ₂ /CuO) are synthesized on copper wires via a facile two‐step method: alkali‐assisted copper surface oxidation, followed by spontaneous redox deposition of manganese dioxide using potassium permanganate under controlled reaction durations. X‐ray diffraction patterns confirmed the presence of Cu, CuO, and copper hydroxide (Cu(OH) ₂ ) phases, while Raman spectra revealed the vibrational signatures corresponding to CuO/Cu(OH) ₂ and MnO ₂ . Tuning the immersion time yields nanorod, needle, and nanosheet architectures; the 40 min sample (MnCu‐40) exhibited the highest specific capacitance among all variants. Spectroscopic analysis revealed an increased Cu charge state (2 ⁺ ) and a reduced Mn charge state in the MnCu‐40, suggesting interfacial charge transfer. Spectro‐microscopic analysis indicated strong electronic coupling and mixed valence states at the Mn‐Cu interface. Under operating conditions, MnO ₆ in MnO ₂ is electrochemically transformed to MnOOH. These findings demonstrate that rationally engineered MnO ₂ /CuO heterostructures on 3D Cu scaffolds offer promising pathways for high‐performance supercapacitor electrodes.