Spectroelectrochemistry of Carbon Nanostructures

Abstract

This review is focused on charge-transfer reactions at carbon nanotubes and fullerenes. The spectroelectrochemistry of fullerenes deals with the spin states of fullerenes, the role of mono-anions and the reactivity of higher charged states in C60. The optical (Vis-NIR) spectroelectrochemistry of single-walled carbon nanotubes (SWNTs) follows changes in the allowed optical transitions among the Van Hove singularities. The Raman spectroelectrochemistry of SWNT benefits from strong resonance enhancement of the Raman scattering. Here, both semiconducting and metallic SWNTs are analyzed using the radial breathing mode (RBM) and G-modes as well as the second order (D, G') and intermediate frequency modes. Raman spectroelectrochemistry of SWNT allows the addressing of index-identified tubes and even single isolated nanotubes. Optical and Raman spectroelectrochemistry of fullerene peapods, C60@SWNT and C70@SWNT indicates effective shielding of the intratubular fullerene (peas). The most striking effect in the spectroelectrochemistry of peapods is the so-called "anodic Raman enhancement" of intratubular C60. Double-walled carbon nanotubes (DWNTs) give a specific spectroscopic response in Vis-NIR spectroelectrochemistry for the inner and the outer tube. They are better distinguishable by Raman spectroelectrochemistry which allows a precise tracing of the specific doping response of outer/inner tubes.

Spectroelectrochemistry at free-standing carbon nanotubes electrodes

“…A characteristic Raman spectrum of the SWCNTs (Fig. 3, red line) shows mainly four bands: the radial breathing mode (RBM), the disorder induced mode (D), the tangential displacement mode (G) and the high frequency two phonon mode (G') [47][48][49][50][51][52]. These bands are completely similar before and after preparation of the film.…”

“…Spectroscopic characterization was performed by Raman spectroscopy, due to the valuable information on the vibrational properties of nanotubes that this technique provides [47][48][49][50][51]. It allows us to verify that the integrity of the SWCNTs is not affected during the electrode fabrication.…”

Perspectives on Electrochemical Insertion of Lithium in Carbon Nanotubes

“…6,7 These pioneering investigations have unambiguously demonstrated that SWNTs give rise to reversible capacities outperforming those theoretically predicted for graphite, that is, 460 versus 372 mAh/g, which is equivalent to a Li 1.23 C 6 stoichiometry. A setback is that initially a large irreversible capacity of 1200 mAh/g evolved.…”

High Levels of Electrochemical Doping of Carbon Nanotubes: Evidence for a Transition from Double-Layer Charging to Intercalation and Functionalization

“…11 On the other hand, a finer tuning of the added charge in the SWNTs can be accomplished electrochemically by varying the potential at their contact interface with an electrolyte solution. 3,12,13 In this case, the electrolyte ions do not readily penetrate the SWNT ropes. Instead, during the initial stages of electrochemical doping in potentiostatic mode, they form a charged double layer only with the external surface of the ropes.…”

“…Instead, during the initial stages of electrochemical doping in potentiostatic mode, they form a charged double layer only with the external surface of the ropes. 3,[12][13][14][15] This is of key importance for SWNT applications as actuators, because SWNT expansion or contraction can be related to the transferred charge, which in the double-layer model can be calculated from the applied voltage. 12,13 On the other hand, intercalation can also be performed electrochemically when galvanostatic mode is applied.…”