Comparison of Cluster Formation, Film Structure, Microwave Conductivity, and Photoelectrochemical Properties of Composites Consisting of Single-Walled Carbon Nanotubes with C_(60), C_(70), and C_(84)

摘要

The cluster formation, electrophoretically deposited film structures, microwave conductivity, and photoelectrochemical properties of the composites consisting of single-walled carbon nanotube (SWNT) with C_(60), C_(70), or C_(84) have been systematically compared for the first time. In an ortho-dichlorobenzene (ODCB)-acetonitrile mixture, the higher fullerenes (i.e., C_(70) and C_(84)) were found to form single composite clusters exclusively with highly soluble SWNT bearing bulky swallow-tailed substituents (f-SWNT). These are in marked contrast with the unselective formation of three different clusters in the C_(60)-f-SWNT composites. Electrophoretic deposition of the composite clusters yielded the corresponding films on nanostructured SnO2 electrodes. The microwave conductivity measurements revealed the occurrence of electron transfer from C_(70) to f-SWNT, followed by electron transportation through f-SWNT, in addition to electron hopping through C_(70) molecule arrays due to the alignment of C_(70) on the sidewalls of f-SWNT in the C_(70)-f-SWNT film. The C_(70)-f SWNT photoelectrochemical device exhibited higher incident photon-to-current efficiency (IPCE) value (26% at 400 nm) than the C_(60)-f-SWNT device (18%). The higher IPCE value results from selective formation of the single composite film, in which the SWNT network is covered with C_(70) molecules, and the high electron mobility (2.4 cm~2 V~(-1) s~(-1)) through the C_(70)-SWNT network. In contrast, the C_(84)-f-SWNT photoelectrochemical device revealed poor photocurrent generation (4.8%) owing to the inefficient electron injection from C_(84) radical anion (C_(84)/C_(84)~(·-) ≈ 0.0 V vs NHE) to the SnO2 electrode (E_(CB) = 0 V vs NHE) directly or indirectly despite the exclusive formation of the single composite clusters. Thus, the results obtained here will provide valuable information on the design of molecular devices based on carbon nanotubes and fullerenes.