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Author: search.filters.author.Obata, MichikoSubject: search.filters.subject.asymmetric supercapacitor

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    Hydrothermal Synthesis of MnO2 and Hemp-Derived Activated Carbon Composites for Tailored Electrochemical Performance
    (2026-07-22)
    Klangvijit, Kanisorn
    ;
    Bowornthommatadsana, Khemjiranee
    ;
    Reilly, Mayuree Phonyiem
    ;
    Obata, Michiko
    ;
    Fujishige, Masatsugu
    This study investigates hydrothermal synthesis of manganese dioxide composited with hemp-derived activated carbon (MnO<inf>2</inf>/AC) as electrodes for supercapacitors. The effects of key hydrothermal parameters, including carbon ratio, reaction temperature, and reaction time were systematically examined. Phase-pure α-MnO<inf>2</inf> was uniformly anchored on carbon framework. Morphology of MnO<inf>2</inf> evolved from nanowalls to well-defined nanorods with increasing reaction temperature and time. Meanwhile, the specific surface area of MnO<inf>2</inf>/AC decreased from 1712 to 1538 m<sup>2</sup> g<sup>−1</sup> due to partial pore blocking, while a predominantly mesoporous structure was retained. Electrochemical measurements in 1 M Na<inf>2</inf>SO<inf>4</inf> demonstrate that the optimized MnO<inf>2</inf>/AC composites achieve a specific capacitance of 216.8 F g<sup>−1</sup> at 1 A g<sup>−1</sup>. Charge-storage mechanism analysis reveals a balanced contribution between surface-controlled capacitive processes and diffusion-controlled pseudocapacitance, which is directly correlated with preserved mesoporosity and moderate MnO<inf>2</inf> coverage. When the MnO<inf>2</inf>/AC composites were assembled into an asymmetric supercapacitor using AC as the negative electrode, the device operates stably up to 2.4 V and delivers outstanding cycling stability over 95% after 22,000 charge–discharge cycles at 5 A g<sup>−1</sup>. These results demonstrate that controlled growth of MnO<inf>2</inf>, rather than maximum oxide loading, is essential for optimizing charge-storage mechanisms and achieving high-performance biomass-derived supercapacitor electrodes.