Rational Design of a Hierarchical Candied-Haws-like NiCo₂O₄@Ni,Co-(HCO₃)₂ Heterostructure for the Electrochemical Performance Enhancement of Supercapacitors

Designing core–shell heterostructures with multicomponents, more electroactive sites, hierarchical structures, and stable geometrical configurations is an effective approach to enhance the electrochemical properties of supercapacitors. Herein, we report the fabrication of a hierarchical candied-haws-like NiCo 2 O 4 @NiCo-hydrocarbonate heterostructure on Ni foam (NiCo 2 O 4 @NiCo-HCs), which consists of NiCo 2 O 4 nanowires acting as “rebars” that are tightly strung with NiCo-HC nanoparticles. The strong interfacial reaction between the NiCo 2 O 4 “core” and the NiCo-HC “shell” accelerates the charge transfer within the heterostructure, while the hierarchical structure containing quantities of paths and pores provides fast ion diffusion throughout the whole electrode, hence remarkably boosting the electrochemical performance of a NiCo 2 O 4 @NiCo-HC electrode. As expected, the NiCo 2 O 4 @NiCo-HC electrode shows a high specific capacitance of 3216.4 F g –1 at a current density of 1 A g –1 and 2259.9 F g –1 even at 20 A g –1 (1.6-fold that of the NiCo 2 O 4 electrode and 5.5-fold that of NiCo-HCs). In addition, an assembled asymmetric supercapacitor NiCo 2 O 4 @NiCo-HCs//AC delivers a high energy density of 47.46 Wh kg –1 at a power density of 708.94 W kg –1, together with 96.2% capacitance retention after 6000 cycles, surpassing most of the reported analogues. These results suggest that our hierarchical candied-haws-like heterostructure design is potential for the performance enhancement of supercapacitors.