Enhanced interfacial electron transfer by constructing NiCo-LDH hollow nanocages decorated N-doped graphene quantum dots heterojunction for high-performance supercapacitors

Nickel–cobalt layered double hydroxides (NiCo-LDHs) are highly promising materials for energy storage electrodes. However, the poor conductivity and easy agglomeration limit their practical application. Herein, the novel hollow nanocage architecture of NiCo-LDH nanosheets (H-NiCo-LDH) decorated N-doped graphene quantum dots (N-GQDs) is constructed using zeolitic imidazolate framework-67 (ZIF-67) as self-sacrificed template. The hollow nanocage structure suppresses the agglomeration of nanosheets and enlarges the electrochemical interface, while the decoration of N-GQDs effectively improves electrical conductivity and provides more abundant active sites. More importantly, HRTEM characterization shows the construction of heterojunctions between H-NiCo-LDH and N-GQDs, and the interfacial charge redistribution through p-n heterojunction promotes interfacial electron transfer and enhances redox activity. Consequently, the N-GQD/H-NiCo-LDH electrode delivers a high specific capacitance of 2347 F g−1 (326 mA h g−1) at 1 A g−1 with excellent rate performance (82% capacitance retention at 10 A g−1). The assembled asymmetric supercapacitor by N-GQD/H-NiCo-LDH and active carbon exhibits an energy density of 52.1 W h kg−1 at a power density of 770 W kg−1 with remarkable cycling stability (80.5% capacitance retention after 5000 cycles). The hollow nanocage structure and enhanced electrical conductivity of N-GQDs make the N-GQD/H-NiCo-LDH a highly promising material for electrochemical energy storage applications.