Supercapacitors have attracted considerable attention as a novel class of energy storage devices. Recently, carbon-based materials, in view of their high specific surface area and electrical conductivity, are the most widely used electrodes for supercapacitors. Among carbon materials, onion-like carbons (OLCs) and carbon nanotubes (CNTs)are utilized to achieve high performance of supercapacitors, since their surfaces are much easier to access for electrolyte ions, compared with other materials (e.g., porous carbons). We investigated the structure and capacitance of electrical double layers (EDLs) formed exohedrally near the electrodes made of OLCs and CNTs, by performing molecular dynamics simulations of supercapacitors composed of OLCs and CNTs immersed in room-temperature ionic liquids. We found that the curvature of different sized OLCs/CNTs plays a dominate role of the formation of EDLs and the capacitive performance of supercapacitors. First, the surface charge density of OLC-/CNT-based electrodes increases nearly linearly with the potential applied on EDLs, resulting in an almost flat shape of the differential capacitance versus the potential. This observation is qualitatively different from that near planar electrodes. Second, the EDL capacitance increases with the electrode curvature or as the radius of an OLC or CNT decreases, in line with theoretical predictions. Third, the investigation of temperature influence on the capacitive behavior shows that, the capacitance of EDLs near OLCs increases with increasing temperature while, in contrast, CNT-based supercapacitors exhibit the capacitance almost independent on temperature.

Exohedral supercapacitors with electrodes of carbon nanotubes and onions

245th National Meeting (2013)

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