One-step synthesis of mesoporous MnO2/carbon sphere composites for asymmetric electrochemical capacitors

Abstract

Whisker-like MnO₂/carbon sphere (MnO₂/C) composites with a mesoporous structure are synthesized through an easy one-step hydrothermal method using glucose as the carbon source without any catalyst or template. Highly porous interconnected MnO₂ nanowhiskers are uniformly coated on the surface of the carbon spheres to construct a mesoporous architecture. A high-voltage asymmetric electrochemical capacitor (EC) is assembled with active carbon as the negative electrode and MnO₂/C spheres as the positive electrode in a neutral aqueous 5 M LiNO₃ solution as an electrolyte. This aqueous electrolyte-based asymmetric EC is reversibly cycled within a wide voltage region of 0–2.0 V. Moreover, a high specific capacitance of 307.6 F g⁻¹, a superior long-term cyclic stability and a nearly 96.6% capacitance retention after 1000 cycles are observed.