Self-assembly of ultrathin MnO2/graphene with three-dimension hierarchical structure by ultrasonic-assisted co-precipitation method

•3D hierarchical ultrathin MnO2/graphene is first prepared by ultrasonic-assisted co-precipitation method.•Time-dependent experiments are carried out to investigate formation mechanism.•Hierarchical MnO2 is formed through self-assembly and Ostwald ripening process.•The composite delivers a capacitance of 216 F g−1 at 1 A g−1 with capacity retention of 89.3% after 2000 cycles.

Hierarchical ultrathin nanostructure MnO2 on graphene sheets are first prepared through ultrasonic-assisted co-precipitation method. The possible growth mechanism of the nanocomposite is discussed by monitoring the early growth stages. It is shown that the formation of the hierarchical structure MnO2 follows a typical self-assembly and Ostwald ripening process. The dispersion of nanoscale thin MnO2 flakes with thicknesses of about 5–10 nm on the graphene helped to increase the contact area of MnO2 with electrolyte, reduce the diffusion and migration length of the ions and increase the electrochemical utilization of MnO2. Electrochemical characterization demonstrate that the hierarchical MnO2/graphene are capable of delivering specific capacitance of 216 F g−1 at the current density of 1 A g−1. A capacity retention of 89.3% can be maintained after 2000 continuous charge–discharge cycles. The method provides a facile and straightforward approach to synthesize hierarchical of MnO2 onto the graphene and may be readily extended to the preparation of other classes of hybrids based on graphene sheets for technological applications.

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