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Hydrothermal Synthesis of MnO2 and Hemp-Derived Activated Carbon Composites for Tailored Electrochemical Performance
Author(s)
Klangvijit, Kanisorn
Bowornthommatadsana, Khemjiranee
Obata, Michiko
Fujishige, Masatsugu
Takeuchi, Kenji
Endo, Morinobu
Date Issued
July 22, 2026
Type
Article
Abstract
This study investigates hydrothermal synthesis of manganese dioxide composited with hemp-derived activated carbon (MnO2/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-MnO2 was uniformly anchored on carbon framework. Morphology of MnO2 evolved from nanowalls to well-defined nanorods with increasing reaction temperature and time. Meanwhile, the specific surface area of MnO2/AC decreased from 1712 to 1538 m2 g−1 due to partial pore blocking, while a predominantly mesoporous structure was retained. Electrochemical measurements in 1 M Na2SO4 demonstrate that the optimized MnO2/AC composites achieve a specific capacitance of 216.8 F g−1 at 1 A g−1. 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 MnO2 coverage. When the MnO2/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−1. These results demonstrate that controlled growth of MnO2, rather than maximum oxide loading, is essential for optimizing charge-storage mechanisms and achieving high-performance biomass-derived supercapacitor electrodes.
Citation
Advanced Engineering Materials, 28(14), 2026