Ionic liquid-functionalized partially exfoliated multiwalled carbon nanotubes for high-performance supercapacitors

Abstract

Partially exfoliated multiwalled carbon nanotubes (PEMWNTs) have great potential to play a major role in electrochemistry, because they have a combination of unique properties of multiwalled carbon nanotubes (MWNTs) and graphene such as high electrical conductivity, high surface area and porosity. In the present study, we have synthesized partially oxidized MWNTs by Hummers method with modest modification and exfoliated to unravel few of the outer layers. Furthermore, the surface of PEMWNTs was functionalized with an ionic liquid (PEMWNTs/IL). The specific capacitance of supercapacitor, fabricated with PEMWNTs/IL, was found to be 242 F g⁻¹ at 2 A g⁻¹ current density, which is 85% higher than that of PEMWNTs-based supercapacitors. The PEMWNTs/IL supercapacitor gains almost 2-fold improvement in energy density along with good cyclic stability. Nyquist plot clearly suggested that charge transfer resistance is significantly reduced by ionic liquid functionalization, but the electron transfer among PEMWNTs is not affected. The low frequency region of the Nyquist plot suggests the charge storage in the wrinkles and folds of unraveled graphene layers.