Electrochemical Properties of the Supramolecular Assembly of Ruthenium(II)-bipyridine Complex with Single-Walled Carbon Nanotubes

The supramolecular assembly of Ru-bipyridine complex, coded Z-907Na, with single-walled carbon nanotube (SWNT) exhibits unique redox behavior, which is applicable for the nanotube wiring of LiFePO4 (olivine). Cyclic voltammograms of thin films of Z-907Na/SWNT reveal two pairs of peaks labeled C-1 and C-2 with formal redox potentials of ca. 3.6 and 3.8 V vs Li/Li+, respectively, indicating two surface-confined redox couples. The same behavior was also found for the Z-907Na adsorbed on carbon black, but not for the Z-907Na adsorbed on Al2O3 or dissolved in the electrolyte solution. In these cases, a single diffusion-controlled voltammogram is observed, with one redox couple at ca. 3.6 V vs Li/Li+. The diffusion coefficients equal 7.8x10(-10) cm(2)/s (for Z-907Na adsorbed on Al2O3) or 1.5x10(-6) cm(2)/s (for Z-907Na in solution). An interpretation is suggested that the C-1 peak is for a hydrophilic interaction, that is anchoring of Z-907Na to the carbon surface via carboxylic groups, and the C-2 peak is for a hydrophobic anchoring, that is interaction with the carboxyl-free bipyridine ligand with the carbon surface. The existence of C-1/C-2 peaks provides further insight into the nanotube wiring of LiFePO4 (olivine) using various nanotubes.