Electrochemical Capacitances of Well-Defined Carbon Surfaces

Abstract

Reported is the capacitive behavior of homogeneous and well-defined surfaces of pristine carbon nanofibers (CNFs) and surface-modified CNFs. The capacitances of the well-defined CNFs were measured with cyclic voltammetry to correlate the surface structure with capacitance. Among the studied pristine CNFs, the edge surfaces of platelet CNFs (PCNF) and herringbone CNFs were more effective in capacitive charging than the basal plane surface of tubular CNF by a factor of 3-5. Graphitization of PCNF (GPCNF) changed the edge surface of PCNF into a domelike basal plane surface, and the corresponding capacitances decreased from 12.5 to 3.2 F/g. A chemical oxidation of the GPCNF, however, recovered a clear edge surface by removal of the curved basal planes to increase the capacitance to 5.6 F/g. The difference in the contribution of the edge surface and basal-plane surface to the capacitance of CNF was discussed in terms of the anisotropic conductivity of graphitic materials.

Influence of structural and textural parameters of carbon nanofibers on their capacitive behavior

“…Notably, considerably higher values were recorded for herringbone and platelet CNFs, with open graphitic edges on their surface, compared to the tubular type, for which the basal planes are exposed to electrolyte ions. The results obtained are in line with the finding of Kim et al [18] that the edge surfaces of CNFs promote charge storage. Kim et al synthesized also a series of CNFs with different graphitic layers alignment.…”

“…However, pure CNFs/CNTs as capacitor electrode materials can only supply relatively low capacitance values, i.e., from 5 to 30 F g -1 , due to their moderate surface area (up to 400 m 2 g -1 ) [18][19][20][21]. It has been reported that CNTs with structural defects exhibit the higher gravimetric capacitance than purified and defectfree ones [18,22].…”

“…However, pure CNFs/CNTs as capacitor electrode materials can only supply relatively low capacitance values, i.e., from 5 to 30 F g -1 , due to their moderate surface area (up to 400 m 2 g -1 ) [18][19][20][21]. It has been reported that CNTs with structural defects exhibit the higher gravimetric capacitance than purified and defectfree ones [18,22]. The capacitance of CNFs/CNTs can be enhanced through development of their surface area by chemical activation [23] and air treatment [24] or the introduction of oxygen and nitrogen functional groups into their surface to provide pseudocapacitance [25][26][27].…”

“…Kim et al [18] studied the capacitive behavior of welldefined CNF surfaces. They reported that the capacitance values for CNFs with exposed graphitic edges, such as herringbone and platelet, are several times higher than for tubular CNFs.…”

“…Unfortunately, the impact of the specific surface area on the capacitance of CNFs has been omitted. The diameter of CNFs may be another factor influencing the electrochemical performance [18].…”