We present a study on the pseudocapacitive properties of birnessite-type MnO
2
grafted on highly graphitized onion-like carbon (OLC/MnO
2
). In a three-electrode setup, we evaluated two different substrates, namely a platinum disc and nickel foam. The OLC/MnO
2
nanohybrid exhibited a large specific capacitance (C
sp
) of 295 and 323 F g
-1
(at 1 A g
-1
) for the Pt disc and Ni foam, respectively. In addition, the Ni foam substrate exhibited much higher rate capability (power density) than the Pt disc. A symmetrical two-electrode device, fabricated with the Ni foam, showed a large C
sp
of 254 F g
-1
, a specific energy density of 5.6 W h kg
-1
, and a high power density of 74.8 kW kg
-1
. These values have been the highest for onion-based electrodes so far. The device showed excellent capacity retention when subjected to voltage-holding (floating) experiments for 50 h. In addition, the device showed a very short time constant ([small tau] = 40 ms). This high rate handling ability of the OLC/MnO
2
nanohybrid, compared to literature reports, promises new opportunities for the development of aqueous-based pseudocapacitors.