Molecular Wiring of Olivine LiFePO₄ by Ruthenium(II)-Bipyridine Complexes and by Their Assemblies with Single-Walled Carbon Nanotubes

The undoped and carbon-free olivine, LiFePO4 was bonded with 5% PVDF, and deposited on F-doped SnO2 support (FTO). The electrodes were modified by a monolayer of three different complexes: NaRu(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine)(NCS)2, coded as Z-907Na, Ru-bis(4,4′-diethoxycarbonyl-2,2′-bipyridine)(4,4′-dicarboxylic acid-2,2′-bipyridine), coded Z-974, and Ru-bis(4,4′-dicarboxylic acid-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine), coded Z-975. These complexes have redox potentials from 3.5 to 4.45 V versus Li/Li+ and are active for molecular wiring of LiFePO4. The Ru-complexes contacting FTO are reversibly oxidized, which allows the holes to be transported via the adsorbed monolayer across the olivine surface, where a subsequent chemical delithiation occurs toward FePO4. The supramolecular assembly of Z-907Na with single-walled carbon nanotubes (SWNT) is more active for molecular wiring than pure Z-907Na. In this case, the LiFePO4/FePO4 system can be charged/discharged by currents larger by 1 order of magnitude, and the performance of the assembly depends on the type of SWNT. This study improved our understanding of molecular wiring in general, and the enhancement of wiring activity by SWNT in particular.