Halloysite nanotube@N-doped graphene heterostructure enabled advanced potassium ion hybrid capacitor anode

Graphene is considered one of the most promising candidates for potassium ion hybrid capacitor (PIHC) anode due to its excellent electrical conductivity and short ion diffusion pathway. However, the relatively weak adsorption ability for potassium ion (K+) and poor K-storage ability of graphene hinder further large-scale application. Herein, a three-dimension electronic modulation strategy is proposed to introduce the electron deficient in graphene by fabricating a stable heterostructure with wrapping nitrogen-doped graphene (NG) on halloysite nanotube (HNTs) noted as HNTs@NG. The electronic structure of graphene is modulated in two-dimension (2D) plane direction through doping N atoms and perpendicular to 2D plane through forming covalent bonds between carbon atoms and oxygen atoms. The graphene with fine-regulated electronic structure delivers a high rate capability (387.1 mA h g−1 at 0.05 A g−1) and good capacity retention (105.8 mA h g−1 at 1.0 A g−1 over 2000 cycles) of HNTs@NG, and further insures energy density and cycle stability of as-developed PIHC. This finding offers an effective way to modulate electron structure of graphene to achieve the development advanced PIHC.