MOF-derived ZnCo2O4@NiCo2S4@PPy core-shell nanosheets on Ni foam for high-performance supercapacitors.

The ZnCo2O4@NiCo2S4@PPy core-shell nanosheets material is prepared by directly growing leaf-like ZnCo2O4 nanosheets derived from the metal-organic framework (MOF) on Ni foam (NiF) via chemical bath deposition and annealing methods and then combining with NiCo2S4 and PPy via electrodeposition methods. The special core-shell structure formed by MOF-derived ZnCo2O4, NiCo2S4 and PPy creates a bi-interface, which could significantly promote the contact between electrode and electrolyte, provide more active sites and accelerate electron/ion transfer. And the combination of these three materials also produces a strong synergistic effect, which could further improve the capacitive performance of the electrode. Therefore, the ZnCo2O4@NiCo2S4@PPy/NiF electrode exhibits the maximum areal capacitance (3.75 F cm-2) and specific capacitance (2507.0 F g-1) at 1 mA cm-2 and 0.5 A g-1, respectively. Moreover, its capacitance retention rate is still 83.2% after 5000 cycles. In addition, a coin-type hybrid supercapacitor is assembled and displays a high energy density of 44.15 Wh kg-1 and good cycling performance.