Synthesis and electrochemistry of multiwalled carbon nanotube films directly attached on silica substrate

Abstract

Vertically aligned multiwalled carbon nanotubes (MWCNT) on silica substrate were selectively produced by the procedure of chemical vapor deposition (CVD). For the synthesis of the MWCNT films, either acetonitrile (ACN) or benzene (BZ) was used as carbon sources while ferrocene (FeCp2) was adopted as catalyst. The packing organization of the aligned carbon nanotubes on the silica substrate, and thus the degree of disorder of the produced MWCNT films, was found to be different. Namely, the MWCNT2 film, produced upon decay of BZ, seems to be more disordered compared to MWCNT1, produced upon decomposition of ACN. In order to examine their prospective application as electrodes for the detection of electroactive compounds in organic solvent media, the techniques of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed. FeCp2 was selected as the suitable standard electroactive substance for probing the fabricated MWCNT electrodes, in view of the fact that FeCp2 undergoes a fast one-electron oxidation process forming the ferrocenium cation (FeCp2+), which is rather stable during the time scale of the experiments. All electrochemical experiments were performed in ACN as solvent medium including n-tetrabutylammonium hexafluorophosphate as supporting electrolyte at room temperature. The extracted CV and EIS results were compared with those obtained using glassy carbon electrode. The findings demonstrate the successful detection of FeCp2 in ACN at both MWCNT films. However, among the films investigated, the electrode produced upon decay of BZ seems to be better capacitor, most probably due to its higher surface area as well as to its small film thickness. Evidently, the high degree of disorder, which has been observed for MWCNT2, plays an important role for the increase of its effective surface area and thus, its capacitance. It is, however, very interesting that the more disorder MWCNT2 film provides, the greater charge transfer resistance.