▎ 摘　　要

Three-dimensional graphene foam (3D GF) is one of the promising candidates due to its fascinating characteristics. In the paper, we reported a simple hydrothermal method to fabricate hierarchical alpha-MnO2 nanotube@delta-MnO2 nanoflake on GF (GF@MNT@MNF) as a lightweight and free-standing electrode of supercapacitor. The 3D GF could serve as an ideal supporter to grow MnO2 active material, and MnO2 mass percentage affects significantly on the electrochemical properties of the composite electrode. When the mass percentage of MnO2 is 60%, a maximum specific capacitance of 202 F.g(-1) with respect to the entire electrode and 336 F.g(-1) relative to active material is achieved. The GF@MNT@MNF electrode presents a remarkable cyclic stability (maintaining about 97% of original capacitance over 5000 cycles). The excellent electrochemical performance of the GF@MNT@MNF electrode is resulted from the combination of the lightweight, flexible, conductive GFs and MnO2 hierarchical structure with large contacting interface and proper space distribution. Furthermore, an asymmetric supercapacitor based on GF@MNT@MNF composites was assembled, which showed a great energy density of 23.2 Wh.kg(-1) under a power density of 119.9 W.kg(-1) in wide potential range of 0-1.8 V. The research may provide a method for lightweight, freestanding and high-performance electrode material for efficient and convenient energy storage device. (C) 2021 Elsevier B.V. All rights reserved.