Design of ZIF-67 nanoflake derived NiCo-LDH/rGO hybrid nanostructures for aqueous symmetric supercapattery application under alkaline condition

Abstract

Well-defined polyhedral ZIF-67 metal-organic frameworks (MOFs) are usually synthesized using methanol as solvent. In this work, methanol is replaced with deionized water as a solvent to synthesize ZIF-67 MOFs with unique nanoflake morphology. The ZIF-67 nanoflakes are synthesized directly by in situ method on reduced graphene oxide (rGO) to obtain ZIF-67/rGO-x precursors which are further transformed into NiCo-layered double hydroxide nanocomposites (NiCo-LDH/rGO-x, x = 10, 30, 50 and 90 mg of rGO). The NiCo-LDH/rGO-x nanostructured composites are found to be excellent materials for battery type supercapacitor (supercapattery) applications. Among these samples, the NiCo-LDH/rGO-30 composite gives maximum specific capacity of 829 C g−1 (1658 F g−1) at a current density of 1 A g−1 and high rate capability. The as fabricated 2-electrode symmetric Swagelok device delivered a high energy density of 49.2 Wh kg−1 and a power density of 4511 W kg−1, and enabled us to glow red, blue and white LED bulbs using three coin cells. The device can show good capacity retention even after 3000 continuous charge–discharge cycles. The NiCo-LDH/rGO-30 composite, in situ derived from ZIF-67 MOF in combination with optimal amount of rGO, is an excellent material to deliver both high energy density and high power density in supercapattery devices.