Scalable sonochemical synthesis of petal-like MnO₂/graphene hierarchical composites for high-performance supercapacitors

The past decade has witnessed substantial achievements on electrochemical energy storage in employing graphene-based composites; however, of which have been usually produced on a laboratory scale with a limited compatibility with future industrialization. Herein a facile, cheap, and scalable sonochemical method was developed to prepare MnO₂/graphene composite electrodes for supercapacitors. Petal-like MnO₂ arrays were densely grown on the surface of graphene oxide followed by annealing at 220 °C under an air atmosphere. The as-fabricated MnO₂/graphene hierarchical composite electrodes deliver 292.9 and 156.1 F/g at 5 and 100 mV/s, respectively, showing higher specific capacitance and better rate capability compared to the MnO₂ electrode. An excellent cyclability with a capacitance retention as high as 91.5% was also achieved for the composite electrodes after running 1000 cycles. Such excellent electrochemical performances are ascribed to the robust composite structure and synergetic contribution from petal-like MnO₂ arrays and conductive graphene sheets.