Résumé
Multi-walled carbon nanotubes (MWCNTs) were prepared through microwave-assisted pyrolysis of ethanol to enhance the electron transfer of expanded graphite (EG). Three kinds of Fe-containing catalyst precursors (ferric nitrate, citric acid-enhanced ferric nitrate and ferrocene) were designated in the present work to investigate the influences of catalyst states on the formation of MWCNT. The cyclic voltammograms and electrochemical impedance of the prepared specimens were characterized. Furthermore, the microstructures of catalyst-loaded EG before and after microwave treatment were investigated by means of SEM and TEM. The results show that the growth of MWCNT under microwave treatment is determined by the state of catalyst and only nanoscaled Fe-containing catalysts favor the formation of MWCNT. The ferric nitrate tends to grow up into submicron Fe2O3 particles, which impedes the growth of MWCNT. In comparison, citric acid enhances the dispersion of ferric nitrate, allowing the growth of MWCNT. Ferrocene possesses dual functions, namely it assures well distribution of nanoscaled catalysts and is also responsible for the growth of first generation of MWCNT. With the growth of MWCNT on EG, the anodic peak current densities and charge transfer resistance of the MWCNT modified EG outperform those of pure EG remarkably.