(335f) Marcus Type Electron Transfer between Molecular Dopants and Pristine (n,m) Single-Walled Carbon Nanotubes at the Solid-Liquid Interface

The concept of
electrical energy generation based on asymmetric chemical doping of
single-walled carbon nanotube (SWNT) papers is presented. We explore 27 small,
organic, electron-acceptor molecules that are shown to tune the output
open-circuit voltage (V_OC) across three types of pristine
SWNT papers with varying (n,m)
chirality distributions. A considerable enhancement in the observed V_OC,
from 80 to 440 mV, is observed for SWNT/molecule acceptor pairs that have
molecular volume below 120 ų and lowest unoccupied molecular
orbital (LUMO) energies centered around −0.8 eV. The electron transfer
(ET) rate constants driving the V_OC generation are shown
to vary with the chirality-associated Marcus theory, suggesting that the energy
gaps between SWNT and the LUMO of acceptor molecules dictate the ET process.
When the ET rate constants and the maximum V_OC are
plotted versus the LUMO energy of the acceptor organic molecule, volcano-shaped
dependencies, characteristic of the Marcus inverted region, are apparent for
three distinct sources of SWNT papers with modes in diameter distributions of
0.95, 0.83, and 0.75 nm. This observation, where the ET driving force exceeds
reorganization energies, allows for an estimation of the outer-sphere
reorganization energies with values as low as 100 meV
for the (8,7) SWNT, consistent with a proposed image-charge modified Born
energy model. These results expand the fundamental understanding of ET transfer
processes in SWNT and allow for an accurate calculation of energy generation
through asymmetric doping for device applications.

References:

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