Epitaxial growth of NixCo3-xS4 nanoflakes from co-based Prussian blue analog for high-performance pseudocapacitors

In this work, a NixCo3-xS4/PBA (Prussian blue analogue) heterostructure is obtained via a facile epitaxial growth method, forming a flower-like structure with NixCo3-xS4 nanoflakes standing independently on PBA. The 2D NixCo3-xS4 nanoflakes can provide sufficient reaction sites for charge storage, while the PBA core can facilitate quick ion transportation during charge/discharge process. Moreover, it has been shown that the growth of NixCo3-xS4 nanoflakes from PBA is a time-dependent reaction that could regulate the electronic state density of Co, Ni and S along the interface of NixCo3-xS4 and PBA. EELS and DFT calculations reveal that the formation of heterogeneous interface between NixCo3-xS4 nanoflakes and PBA results in an electron deficient region of NixCo3-xS4, which benefits the adsorption and reaction of OH– on NixCo3-xS4. With the structural and compositional merits, the NixCo3-xS4/PBA obtained with reacting for 7 h exhibits the superior specific capacitance and good rate capability with retaining 91.5 % of initial capacitance as well as quick charge response. The assembled NixCo3-xS4/PBA//AC asymmetric supercapacitor exhibit an energy density of 52.2 Wh kg−1, which could light 14 LED lamps with maintaining the brightness for 5 min. Therefore, the design of 3D NixCo3-xS4/PBA and the systematical investigation on the structural evolution as well as the concomitant electron configuration regulation may not only inspire the design of high-performance electrode materials for supercapacitors, but also be valuable for understanding the charge storage mechanism on heterostructures.