Planar thin film supercapacitor based on cluster-assembled nanostructured carbon and ionic liquid electrolyte

The fabrication of a planar supercapacitor based on cluster-assembled nanostructured carbon (ns-C) thin films deposited by supersonic cluster beam deposition and ionic liquid as electrolyte has been demonstrated. Cluster-assembled carbon has a density of about 0.5 g/cm3 and a highly disordered structure with predominant sp2 hybridization, high surface roughness and granular nanoscale morphology. The electric double layer capacity of ns-C films (thickness variable in the range of 140–500 nm) was investigated by electrochemical impedance spectroscopy and cyclic voltammetry employing four different hydrophobic room-temperature ionic liquids featuring the same anion and with different cations as electrolyte. Evidence of good impregnation of the ns-C nanoporous matrix by the different ionic liquids was found. The highest EDL capacity, 75 F/g, was obtained by using [Bmim][NTf2], the ionic liquid with the shortest alkyl chain. Using [Bmim][NTf2] a supercapacitor with single electrode area of 0.2 cm2 and specific capacity of ∼80 μF/cm2 was obtained.