Two-step approach of fabrication of three-dimensional MnO₂-graphene-carbon nanotube hybrid as a binder-free supercapacitor electrode

This paper describes the fabrication and characterization of a three-dimensional (3D) MnO₂-graphene (GR)-CNT hybrid obtained by combining electrochemical deposition (ELD)-electrophoretic deposition (EPD) and chemical vapor deposition (CVD). Firstly, 3D MnO₂-graphene oxide (GO) is fabricated via ELD-EPD. Secondly, the catalyst and xylene are mixed with solution of certain concentration. Thirdly, catalyst is loaded on the surface of MnO₂-GO when the solution is sprayed into the furnace. Forth, MnO₂-GO is restored to MnO₂-GR at high temperature, meanwhile, MnO₂-GR is served as a substrate to grow CNT, which is beneficial to provide high speed channel for carrier and obtain pseudocapacitance of MnO₂. The as-prepared hybrid is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray Diffraction (XRD) and Raman spectroscopy (Raman), and their supercapacitor properties are also investigated. The results show that a high specific capacitance of 330.75 F g^-1 and high energy density of 36.68 Wh kg^-1 while maintaining high power density of 8000 W kg^-1 at a scan rate of 200 mV s^-1. Furthermore, the hybrid displays a high specific capacitance of 187.53 F g^-1 at ultrahigh scan rate of 400 mV s^-1. These attractive results demonstrate that the hybrid is a promising electrode material for high performance supercapacitors.