Role of surface fluorine in improving the electrochemical properties of Fe/MWCNT electrodes

In this study, we investigated the role of the surface fluorine in carbon electrode materials in the energy storage of the corresponding electric double-layer capacitors (EDLCs). And in order to reach this goal, the highly graphitic material multi-walled carbon nanotubes (MWCNTs) were fluorinated to minimize the changes in the textural properties after fluorination and the textural, surface chemical, and electrochemical properties of the resulting MWCNTs were evaluated. The fluorination of the MWCNTs did not change their textural properties because of their highly graphitic properties. The surface fluorine contents of the fluorinated MWCNTs varied depending on the fluorination conditions. The electrochemical properties of the fluorinated MWCNT-based electrodes improved by 31.4–37.7% compared to those of the pristine MWCNTs, depending on the current-density load (0.2–1.5 A/g). The increase in the retained capacitance is due to the surface fluorination of the MWCNTs. The role of the surface fluorine on the MWCNTs for the improved electrochemical properties of the fluorinated MWCNT-based electrodes is explained using a simple computational study. The surface fluorine induces charge transfer on the surface of the MWCNTs, resulting in a more nucleophilic surface that improves the interaction between the surface of the fluorinated MWCNTs and H3O+.