Vertical graphene nanosheets as interface current-collector for enhanced charge-storage kinetics of bimetallic MOF nano-rods and asymmetric solid-state supercapacitors

Vertical graphene nanosheets (VGN), also known as vertical-oriented graphene or carbon nanowalls emerge recently for different energy storage devices by virtue of their interesting properties that enable them to bring out as excellent current-collector and templates for the growth of different nanostructures. In the current research, we design the facile synthesis of nano-sized bimetallic NiCo MOF on VGN (NiCo MOF/VGN) to achieve improved storage performance. The enhanced capacitive contribution, wetting nature, and charge-transfer kinetics of NiCo MOF/VGN facilitate an increase in the energy-storage performance in the case of an in-situ (solvothermal) method than the drop-cast method. Further, the comparison also confirms that VGN acts as an excellent current collector for NiCo MOF than carbon paper. Due to the unique morphology of VGN and nano rod-like NiCo MOF structure, the NiCo MOF/VGN composite delivers a specific capacity of 132 mA h g-1 (475 C g-1) and a specific capacitance of 950 F g-1 at 1 A g-1 with a high rate capability of 93.2 % at 10 A g-1. Moreover, the assembled asymmetric solid-state supercapacitor device (NiCo MOF/VGN//PVA + KOH//activated carbon) exhibited a high energy density of 58.1 Wh kg-1 at a power density of 1170 W kg-1 and a high power density of 7 kW kg-1 at an energy density of 36.5 Wh kg-1 with a cycle stability of 88.5 % after 10,000 cycles of charge-discharge.