Ultrafine Ni(OH)2 nanoneedles on N-doped 3D rivet graphene film for high-performance asymmetric supercapacitor

Integrating nanometer-sized active materials into free-standing conductive porous substrates is a highly desirable route to obtain high-performance energy storage devices. Herein, we designed and fabricated a free-standing N-doped 3D rivet graphene (N-3DRG) film with lightweight and bicontinuous 3D porous structures using chemical vapor deposition (CVD). Then, dense lawn-like ultrafine Ni(OH)₂ nanoneedles were deposited onto the outer and inner surfaces of N-3DRG via a hydrothermal process. The N-3DRG film shows excellent conductivity and high specific surface area, which can facilitate the rapid transfer of electrons and provide more surface area for the deposition of active materials. The ultrafine nanometer-sized morphology of the Ni(OH)₂ nanoneedles exposes more active sites to the electrolyte, which significantly accelerates mass transfer and improves the reaction kinetics. Owing to the distinct structural advantages, the Ni(OH)₂/N-3DRG electrode exhibits a high specific capacity of 256.1 mAh g⁻¹ (based on the total mass of the electrode). Furthermore, the as-fabricated Ni(OH)₂/N-3DRG-based asymmetric supercapacitor achieves a rather high energy density of 50.8 Wh kg⁻¹ at an average power density of 452 W kg⁻¹ and excellent cycle stability.