Electron storage in single wall carbon nanotubes. Fermi level equilibration in semiconductor-SWCNT suspensions

The use of single wall carbon nanotubes (SWCNTs) as conduits for transporting electrons in a photoelectrochemical solar cell and electronic devices requires better understanding of their electron-accepting properties. When in contact with photoirradiated TiO2 nanoparticles, SWCNTs accept and store electrons. The Fermi level equilibration with photoirradiated TiO2 particles indicates storage of up to 1 electron per 32 carbon atoms in the SWCNT. The stored electrons are readily discharged on demand upon addition of electron acceptors such as thiazine and oxazine dyes (reduction potential less negative than that of the SWCNT conduction band) to the TO,SWCNT suspension. The stepwise electron transfer from photoirradiated TiO2 nanciparticles -> SWCNT -> redox couple has enabled us to probe the electron equilibration process and determine the apparent Fermi level of the TiO2-SWCNT system. A positive shift in apparent Fermi level (20-30 mV) indicates the ability of SWCNTs to undergo charge equilibration with photoirradiated TiO2 particles. The dependence of discharge capacity on the reduction potential of the dye redox couple is compared for TiO2 and TiO2-SWCNT systems under equilibration conditions.