Highly conductive three-dimensional MnO₂-carbon nanotube-graphene-Ni hybrid foam as a binder-free supercapacitor electrode

Carbon nanotube (CNT)-graphene hybrids grown on porous Ni foam are used as substrates to immobilize MnO₂ nanoflakes, thus forming three-dimensional (3D) MnO₂-CNT-graphene-Ni hybrid foam. The as-prepared hybrid materials could be used as supercapacitor electrodes directly without any binder and conductive additives, and fully maintain the high conductivity and high surface-to-volume ratio of CNTs, large pseudocapacitance of MnO₂ nanoflakes and high porosity provided by the framework of Ni foam. The conductivity of the 3D MnO₂-CNT-graphene-Ni foam is as high as 117 S cm^-1 due to the seamless integration of MnO₂ nanoflakes, CNTs, graphene and Ni foam among the 3D frameworks, which guarantee its low internal resistance (1.25 ohm) when compacted into supercapacitor devices. In aqueous electrolytes, the 3D MnO₂-CNT-graphene-Ni based prototype supercapacitors show specific capacitances of ∼251 F g ^-1 with good cycling stability at a current density of 1.0 A g ^-1. In addition, these 3D hybrids also demonstrate their potential in all-solid-state flexible supercapacitors.