 Active carbon (AC) composited with multiwall carbon nanotubes (CNTs) is synthesized through a high-temperature process for application as a negative electrode material of capacitors. Highly porous interconnected CNTs are uniformly coated onto the surface of AC sheet with a large area that reversibly absorbed hydrogen, resulting in a supercapacitor with larger working voltage and higher pseudocapacitance. A MnO2 nanotubes//AC–CNTs asymmetric electrochemical capacitor is assembled within a wide voltage region of 0–2.4 V in 2.0 M Li2SO4 aqueous electrolyte. Moreover, high energy density and power density, as well as superior cycling stability with >92 % capacitance retention over 6000 cycles, are observed. The reversible hydrogen absorption of the negative electrode may have practical applications in supercapacitors with high energy density and power density.