Gill Inspired Hierarchical Wrinkles Of Reduced Graphene Oxide Encapsulated Carbon Nanotubes With Significantly Boosted Supercapacitor Performance

It has long been pursued in the energy storage community that 3D carbon materials can be constructed with 1D carbon nanotubes and 2D graphene in a proper manner that fully develops their appealing synergistic effects of high conductivity and large surface area. However, the present hybrid nanostructures suffer from either weak bonding strength or heavy dependence on high cost processing techniques. Here we report a gill-inspired hierarchical structure created by a simple annealing strategy, where carbon nanotubes are encapsulated in the wrinkles made of reduced graphene oxide, in resemblance to the vessels embedded in the wrinkle-like gill lamellae. The wrinkled structure enables enriched micropore structures and improved specific surface area, while the embedded carbon nanotubes guarantee the enhanced electrical conductivity. Thus, rGO@CNTs@AC (1000) achieved a 75% increase in the specific capacity @ 1 A g-1 (200 F g-1 vs. 120 F g-1) when compared to a commericial AC in 1 M Et4NBF4/PC. In addition, the encapsulation strategy improved the supercapacitor stability by preventing the electrode materials from falling apart during the cycling. After 1000 cycles @ 1 A g-1, the capacity retention rate of rGO@CNTs@AC (1000) remained above 90% while that of AC only maintained around 60%. More importantly, the proposed strategy should be applicable to general electrode materials for further improvement as supercapacitors. This work offers a novel bio-inspired strategy to effectively improve the supercapacitor performance by rationally designed hierarchical nanostructures.