MnO ₂/onion-like carbon nanocomposites for pseudocapacitors

Manganese oxide (MnO 2)/onion-like carbon (OLC) nanocomposites have been synthesized by a hydrothermal method for application as the electrode material of pseudocapacitors. An asymmetric pseudocapacitor was composed of MnO 2/OLC nanocomposites as the working electrode and nickel foam as the counter electrode immersed in an aqueous Na 2SO 4 solution as the electrolyte is assembled. With the presence of OLC, the corresponding specific capacitance is improved from 27.5 to 177.5 F g -1 at 2 A g -1 current charge-discharge rate when compared to that of using pure MnO 2 as the working electrode. Furthermore, only 6.3% decrease of the specific capacitance is observed when the discharge rate is increased from 0.2 to 2 A g -1. Our MnO 2/OLC pseudocapacitors also exhibit a superior cycling stability of 99-101% retention of specific capacitance after 1000 cycles. The results exhibit great potential in developing quick-charge/slow-discharge supercapacitors for practical applications.