Fluorination effect of activated carbon electrodes on the electrochemical performance of electric double layer capacitors

The surface of phenol-based activated carbon (AC) was fluorinated at room temperature with different F2:N2 gas mixtures for use as an electrode material in an electric double-layer capacitor (EDLC). The effect of surface fluorination on EDLC electrochemical performance was investigated. The specific capacitance of the fluorinated AC-based EDLC was measured in a 1 M H2SO4 electrolyte, in which it was observed that the specific capacitances increased from 375 and 145 F g−1 to 491 and 212 F g−1 with the scan rates of 2 and 50 mV s−1, respectively, in comparison to those of an unfluorinated AC-based EDLC when the fluorination process was optimized via 0.2 bar partial F2 gas pressure. This enhancement in capacitance can be attributed to the synergistic effect of increased polarization on the AC surface, specific surface area, and micro and mesopore volumes, all of which were induced by the fluorination process. The observed increase in polarization was derived from a highly electronegative fluorine functional group that emerged due to the fluorination process. The increased surface area and pore volume of the AC was derived from the physical function of the fluorine functional group.

Graphical abstractThe specific capacitance increased significantly after fluorination with a F2:N2 (2:8) gas mixture. This capacitance enhancement was derived from a synergistic effect of the increased polarity that was induced by the formation of the fluorine functional groups and the increase in the specific AC surface area and micro and mesopore volume after fluorination.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights• The unique surface modification method, fluorination, was introduced. • Electrochemically active C–F war introduced by fluorination. • Pore structure was changed by fluorination. • Improved EDLC capacitance was achieved, due to the abovementioned synergistic effect.