Comparison of Cluster Formation, Film Structure, Microwave Conductivity, and Photoelectrochemical Properties of Composites Consisting of Single-Walled Carbon Nanotubes with C60, C70, and C84

Abstract

The cluster formation, electrophoretically deposited film structures, microwave conductivity, and photoelectrochemical properties of the composites consisting of single-walled carbon nanotube (SWNT) with C60, C70, or C84 have been systematically compared for the first time. In an ortho-dichlorobenzene (ODCB)−acetonitrile mixture, the higher fullerenes (i.e., C70 and C84) 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 C60−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 C70 to f-SWNT, followed by electron transportation through f-SWNT, in addition to electron hopping through C70 molecule arrays due to the alignment of C70 on the sidewalls of f-SWNT in the C70−f-SWNT film. The C70−f-SWNT photoelectrochemical device exhibited higher incident photon-to-current efficiency (IPCE) value (26% at 400 nm) than the C60−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 C70 molecules, and the high electron mobility (2.4 cm2 V−1 s−1) through the C70−SWNT network. In contrast, the C84−f-SWNT photoelectrochemical device revealed poor photocurrent generation (4.8%) owing to the inefficient electron injection from C84 radical anion (C84/C84•− ≈ 0.0 V vs NHE) to the SnO2 electrode (ECB = 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.