Porous CoSe₂ nanosheet arrays derived from zeolitic imidazolate frameworks on Ni foam for asymmetric supercapacitors

Porous CoSe₂ nanosheets are prepared on nickel foam by the hydrothermal method using Se powder as the selenium source and a zeolitic imidazolate framework (ZIF-67) as the template. The impact of hydrothermal temperature on the morphological structure and electrochemical performance of the CoSe₂ materials is investigated by characterization with HRTEM, SEM, XRD, and so on, and CV and GCD electrochemical tests. The results show that the CoSe₂-180 electrode material exhibits excellent electrochemical performance, and its unique nanosheet array structure can provide a highly active surface, large superficial area and fast ion transport channels. This is mainly attributed to the fact that the reaction at different hydrothermal temperatures can provide different nanosheet structures. An ordered array structure is most clearly observed at a hydrothermal temperature of 180 °C. In addition, the incorporated ZIF-67 backbone provides a pathway for rapid electron transfer and accommodates the volume expansion of the selenide during charge-discharge processes. Due to the distinct porous structure, the CoSe₂-180 electrode shows a high specific capacity of 269.4 mA h g^-1 at 1 A g^-1 and a distinguished retention rate of 83.7% at 20 A g^-1. After 5000 cycles, the specific capacity can be maintained at 83.4% of the initial value. Moreover, the asymmetric supercapacitor (ASC) device is assembled with CoSe₂-180 as the positive electrode. It displays favorable electrochemical performance with the maximum specific energy of 45.6 W h kg^-1 at a specific power of 800.8 W kg^-1 and an original capacitance retention rate of 81.5% after 5000 cycles.