MnO2/onion-like carbon nanocomposites for pseudocapacitors

Manganese oxide (MnO2)/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 MnO2/OLC nanocomposites as the working electrode and nickel foam as the counter electrode immersed in an aqueous Na2SO4 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 MnO2 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 MnO2/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.