MnO2/onion-like carbon nanocomposites for pseudocapacitors

Abstract

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.