Electrochemical activation of CoP/ZIF-67 hybrid nanostructures for boosting electrochemical performance

CoP/ZIF-67 hybrid nanostructures are synthesized on NF framework through growing polyhedral ZIF-67 blocks on the surface of CoP nanoneedles. The electrochemical activation feature of NF/CoP/ZIF-67 composite is investigated in KOH electrolyte. Under a repeated CV scanning, CoP nanoneedles change into rod structures stacked by thin nanosheets, accompanied with the formation of hexagonal Co(OH)2 nanosheets. The size and thickness of hexagonal nanosheets change with an increasing cycle. Meanwhile, polyhedral ZIF-67 blocks disappear rapidly and generate organic carbon layers on the sample surface, which prevents the recombination and agglomeration of surface nanostructures. A small amount of Ni element can be observed in activated product, which are derived from activated NF substrate. When subjected to 1200 CV cycles, the activated product presents a maximum capacitance of 2890 F g- 1 at 1 A g- 1, greatly higher than the initial capacitance. The improved performance of the activated product is attributed to the microstructure and composition transition of CoP/ZIF-67, the formation of organic carbon layer, and the introduction of active Ni. In addition, asymmetric supercapacitor device is fabricated by using NF/CoP/ZIF-67 electrode and NF/active carbon negative electrode. The device delivers a superior electrochemical performance, including an outstanding cycling stability and a high energy density.