Great efforts have been made on

A proposed mechanism for the effects of the thermal fluorination on the EDLC by MWCNTs 8-Aminoadenine shown in Fig. 9. The fluorine atoms conjugated with the basal or edge planes of the MWCNTs to form semi-covalent or covalent CF bonds. CF functional groups were reported to improve the EDLC performance via enhanced surface polarization [25] and [42]. The presence of heteroatoms (N, O, or F) was hypothesized to make the carbon surface more polar [43]. In the carbon–fluorine bonding, fluorine (4.1) is more electronegative than carbon (2.5), resulting in a negatively charged (δ−) surface. The electronegativity difference of the carbon–hydrogen bonding is 0.4, while the electronegativity difference of the carbon–fluorine bond is 1.6. The electronegativity difference reflects the polarity [43]. The magnitude of the carbon–fluorine bond dipole (δ+–δ−) is larger than the magnitude of the carbon–hydrogen bonding dipole (δ−–δ+). Because electrons move partially from carbon atoms to fluorine atoms to form a negatively charged (δ−) surface, the δ− surface is directly exposed to the electrolyte solution (H2SO4). It was reported dystrophin the H3O+ ions in the H2SO4 electrolyte more easily approach a thermally fluorinated MWCNT surface than an untreated MWCNT surface. As the thermal–fluorination temperature increased, more fluorine functional groups were introduced on the basal planes of the MWCNTs. Moreover, some defects were also produced due to the introduction of fluorine functional groups on the basal planes of the MWCNTs. It was expected that the fluorine functional groups and defects were the electrochemically active sites. These results indicate that thermal fluorination can enhance the specific capacitance and electrochemical properties of MWCNTs.