3D Graphene-Nickel Hydroxide Hydrogel Electrode for High-Performance Supercapacitor

3D graphene-based frameworks with interpenetrating macroporous structures have attracted great interests recently since they can serve as robust matrix for accommodating guest nanoparticles for use in a wide range of applications. Here, an adsorption-hydrothermal strategy is adopted for the in-situ growth of Ni(OH)₂ nanoplates using three dimensional (3D) nitrogen-containing graphene hydrogel (NG) as the substrate. The NG/Ni(OH)₂ nanocomposite hydrogel thus obtained is explored as the monolithic free-standing supercapacitor electrode without adding any other binders or conductive additives. The 3D hierarchical structure of the NG/Ni(OH)₂ nanocomposite can not only provide a large accessible surface area, but also facilitate ion diffusion and charge transport for much improved supercapacitive performance. The gel with Ni(OH)₂ loading of ∼40% achieves a high specific capacitance of 782 F g^-1 at the current density of 0.2 A g^-1, which equals to a specific capacitance of 1748 F g^-1 based on the mass of Ni(OH)₂ alone. Excellent cycling stability of only 10% capacitance loss after 10000 cycles is also achieved due to the robust adhesion between the metal hydroxide and nitrogen containing graphene. Furthermore, high capacitance retention of ∼80% can be achieved when the current density is increased 100 fold from 0.2 to 20 A g^-1.