Electrochemical Performance of MnO2/Graphene Flower-like Microspheres Prepared by Thermally-Exfoliated Graphite

To enhance the electrochemical performance of MnO2/graphene composite, herein, thermally-exfoliated graphite (TE-G) is adopted as a raw material, and a hydrothermal reaction is conducted to achieve the exfoliation of TE-G and the loading of MnO2 nanosheets. Through optimizing the TE-G/KMnO4 ratio in the redox reaction between carbon and KMnO4, flower-like MnO2/G microspheres (MnO2/G-10) are obtained with 83.2% MnO2 and 16.8% residual graphene. Meanwhile, corresponding MnO2/rGO composites are prepared by using rGO as raw materials. Serving as a working electrode in a three-electrode system, MnO2/G-10 composite displays a specific capacitance of 500 F g(-1) at 1 A g(-1), outstanding rate performance, and capacitance retention of 85.3% for 5,000 cycles. The performance is much better than that of optimized MnO2/rGO composite. We ascribe this to the high carbon fraction in TE-G resulting in a high fraction of MnO2 in composite, and the oxygen-containing groups in rGO reduce the resulting MnO2 fraction in the composite. The superior electrochemical performance of MnO2/G-10 is dependent on the hierarchical porous structure constructed by MnO2 nanosheet arrays and the residual graphene layer in the composite. In addition, a supercapacitor assembled by TE-G negative electrode and MnO2/G positive electrode also exhibits superior performance. In consideration of the low cost of raw materials, the MnO2/G composite exhibits great application potential in the field of supercapacitors.