Three-dimensional nanocomposite of graphene/MWCNT hydrogel grafted with Ni–Co hydroxide nanorods as high-performance electrode for asymmetric supercapacitor

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Graphene hydrogels with a three-dimensional (3D) structure have attracted attention as electrode materials for energy storage devices due to their macroscopic architecture and freestanding characteristics. In this work, 3D graphene/MWCNT hydrogel (GCH) with a tunable internal structure was self-assembled through chemical reduction and used as an electrode material for supercapacitor. The added MWCNTs prevent aggregation of graphene sheets and increase available active sites. Furthermore, the high conductivity and strength of MWCNTs greatly tuned the structural and physical properties of the hydrogel. Nickel-cobalt hydroxide nanorods were further grafted on GCH scaffold by a hydrothermal method. Due to its good electrolyte accessibility and fast charge transfer, the resulting GCH-NC shows high specific capacity and outstanding rate performance when it is used as electrode material for supercapacitor. For practical applications, asymmetric supercapacitor is fabricated using GCH and GCH-NC as negative and positive electrode materials, respectively. The fabricated asymmetric supercapacitor exhibits excellent performance with an energy density of 0.36 mWh/cm2 and a high power density of 22.6 mW/cm2 (loading mass: 10.6 mg/cm2). Also, this device possesses outstanding cycle stability with capacity retention of 92% after 25,000 cycles at a current density 10 A/cm2. Therefore, the GCH-NC is expected to be a promising electrode material for high-performance supercapacitor.