Decoration of ultrathin porous zeolitic imidazolate frameworks on zinc-cobalt layered double hydroxide nanosheet arrays for ultrahigh-performance supercapacitors

In this work, ultra-thin zeolitic imidazolate frameworks (ZIFs) layers are coated on Zn-Co layered double hydroxide (LDH) nanosheet electrodes by chemical vapor deposition. The ZIF-coated Zn-Co LDH nanosheets are revealed to present excellent electrochemical performances (specific capacitance of 2068 F g(-1) at scan rate of 1 A g(-1), and retention ratio of 92.6% after 10,000 cycles), which are much higher than those of the untreated ones (specific capacitance of 1444 F g(-1) at 1 A g(-1), and retention ratio of 63.6% after 10,000 cycles). The enhanced electrochemical performance may be attributed to the cavity confinement effect and more active sites exposed by the rough Zn-Co LDH nanosheets coated with ZIFs. Meanwhile, the ZIFs with porous structure and ultra-high specific surface area could promote the redox reaction on the surface of the Zn-Co LDH nanosheets by electrolyte ions storing and adsorbing during the electrochemical process. The surface-coated ZIFs can effectively avoid unnecessary electrochemical reaction between the electrolyte and the electrode material during electrochemical cycling, avoiding irreversible dissolution during cycling. Furthermore, the Zn-Co-130-ZIFs-10h//NC-950 device delivers a higher energy density of 42.5 Wh kg(-1) at a power density of 424 W kg(-1).