One-Step Electrothermal Fabrication of a Tailored Micro/Nanostructured Hybrid of Carbon Fiber and Reduced Manganese Oxide for Binder-Free High-Performance Supercapacitor Electrodes

Hybrid metal oxide electrodes are attractive for high-performance supercapacitors, but conventional fabrication methods often require long processing times and offer limited control over phase composition and microstructure. Here, we report a rapid one-step electrothermal strategy for the fabrication of binder-free carbon/manganese oxide (C/MnO x ) electrodes by Joule heating of manganese nitrate-coated carbon paper. The applied voltage and pulse duration strongly influenced the phase composition and micro/nanostructure of MnO x, resulting in pronounced differences in electrochemical performance. In particular, the electrode prepared at 30 V/0.5 s outperformed that prepared at 15 V/2 s because the high-voltage condition promoted a more favorable MnO x phase composition and an open pine-tree-like hierarchical morphology that improved electrolyte accessibility and ion transport. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy revealed voltage-dependent evolution of MnO x phases, while electron microscopy showed distinct morphological changes from particle-packed coatings to nanosheet-assembled hierarchical structures. The optimized electrode delivered an areal capacitance of 639 mF cm −2 at 0.5 mA cm −2, corresponding to a specific capacitance of 142 F g −1, and retained 130% of its initial capacitance after 10,000 cycles owing to electrochemical activation. These results demonstrate that Joule-heating kinetics provide an effective route for tuning the MnO x phase and morphology for high-performance supercapacitor electrodes.