Graphene–MnO2 nanocomposite for high-performance asymmetrical electrochemical capacitor

• MnO2–graphene nanocomposites are prepared by a simple redox reaction using graphene as a supporting substrate to grow MnO2.
• Ultrathin MnO2 nanoflakes prevent the agglomeration of graphene nanosheets.
• GR–MnO2 (1.45) electrode exhibits a high specific capacitance of 274 F g−1.
• The asymmetrical supercapacitor can cycle reversibly in a voltage of 0–1.8 V and gives a high energy density of 23.9 Wh kg−1.
• 96% of specific capacitance remains after 1000 cycles at a scan rate of 2 A g−1.

Graphene–MnO2 (GR–MnO2) nanocomposites with different MnO2 amounts have been synthesized by a simple redox reaction between GR and KMnO4 at 70 °C, in which GR as a supporting substrate to grow MnO2. Ultrathin MnO2 nanoflakes with a layered structure are dispersed on the surface of GR nanosheets, and the incorporation of MnO2 nanoflakes onto GR prevents the agglomeration of GR nanosheets. GR nanosheet suspension reacted with a KMnO4 solution of 1.45 mmol L−1, the obtained nanocomposite (GR–MnO2 (1.45)) electrode shows a specific capacitance of 274 F g−1 at a scan rate of 10 mV s−1. An asymmetrical electrochemical capacitor is assembled by using GR–MnO2 (1.45) nanocomposite as positive electrode and GR as negative electrode. It can cycle reversibly in a cell potential of 0–1.8 V and gives a high energy density of 23.9 Wh kg−1 and a good cycling performance of about 96% of the initial capacitance after 1000 cycles.

GR–MnO2 nanocomposites were prepared by a simple redox reaction using GR as a supporting substrate to grow MnO2, the incorporation of MnO2 nanoflakes onto GR prevented the agglomeration of GR nanosheets. An asymmetrical electrochemical capacitor based on the GR–MnO2 (1.45) nanomaterial and GR was assembled with a cell potential of 1.8 V, which gave an energy density of 23.9 Wh kg−1. Moreover, the asymmetrical electrochemical capacitor exhibited excellent cycle stability.Figure optionsDownload as PowerPoint slide