Synthesis of morphology controlled NiCo-LDH microflowers derived from ZIF-67 using binary additives and their excellent asymmetric supercapacitor properties

Dodecahedral imidazolium framework-67 (ZIF-67) is synthesized in aqueous solution and used as a sacrificial template for the synthesis of uniform three-dimensional (3-D) hierarchical hexagonal flower-like nickel-cobalt layered double hydroxides (NiCo-LDH) by facile hydrothermal treatment. TEM and SEM results reveal that each microflower is composed of abundant two-dimensional (2D) ultrathin wrinkled nanosheets. The induction of 2,3,5,6-terafluroterephthalic acid (H2tfbdc) and hexamethylenetetramine (HMT) as an additive along with nickel nitrate hexahydrate plays a vital role to tune uniform hierarchical morphology and augmented electrochemical performance. The supercapacitor performance results show that (NiCo-LDH)SHH electrode has the best supercapacitor performance when it is used as a pseudo-capacitor. The maximum specific capacitance is 1765 F g(-1) at the current density of 1 A g(-1) with stable cycling performance. An asymmetric supercapacitor device assembled using (NiCo-LDH)SHH as the positive and activated carbon (AC) as the negative electrode attains a high energy density of 53.31 Wh kg(-1) at a power density of 749.7 W kg(-1) with 84.3% capacitance retention after 6000 cycles. This work provides a novel route for the design and synthesis of two-component hydrotalcite with 2D nanosheets having a large interlayer spacing of 9.3 d(angstrom) and its potential application in electrochemical energy storage.