The composite electrode materials of α-MnO₂/activated carbon (α-MnO₂/AC) were prepared by in-situ hydrothermal deposition using ammonium persulfate as oxidants, manganese sulfate as precursors, ammonium sulfate as templates and self-made activated carbon as supports. X-ray diffraction, scanning electron microscopy and nitrogen adsorption-desorption at 77 K were used to investigate the crystal structure, morphology, specific surface area and porosity of the composites, respectively. Their electrochemical properties were evaluated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The results showed that crystalline α-MnO₂ was well deposited on the AC to produce thin layer crystal α-MnO₂/AC composite material at the optimal MnSO₄ concentration of 0.075 mol• L^－1 in the synthetic process. The specific capacitance of the composite could be as high as 374.5 F•g^－1, 48.2% higher than that of pure AC electrode. The α-MnO₂/AC composite electrode had high stability and the capacity retention was of 95% after a 1000-cycle charge-discharge.

Key words: in-situ hydrothermal deposition, activated carbon, α-MnO₂, electrode material, electrochemical capacitors