Fast Response, Carbon-Black-Coated, Vertically-Oriented Graphene Electric Double Layer Capacitors

Abstract

Development of electrical double layer capacitors using vertically oriented graphene nanosheets with fast response continues. The inherent open morphology of the nanosheets allows efficient access to charge storage surfaces, making them suitable for AC line filtering. However, since the overall surface area is only about a factor of ∼310x over the geometric area, the specific capacitance available remains limited. This work presents utilization of the conventional growth of vertically oriented graphene nanosheets on Ni substrates as the underlying architecture for coating with high surface area carbon black to substantially increase the specific capacitance while retaining the open morphology to allow good frequency response at 120 Hz. The carbon black coating was deposited on ∼1.2 μm and ∼2.5 μm high nanosheets using an aerosol spray method. Deposition times from 0–8 s, in 1 s intervals, provided coatings which translated into a specific capacitance of 2.3 mF/cm2 at 120 Hz (8 s coating) and a volumetric capacitance of 4.6 F/cc (energy storage elements). Improvements in the uniformity of the carbon black coatings suggest that much higher specific capacitances are possible. COMSOL models of high density VOGN grown to 10 μm high and covered uniformly with 100 nm of carbon black coating suggest a capacitance of ∼42 mF/cm2 with acceptable frequency response at 120 Hz can be achieved.