The probing of local charge with sulfur encapsulated in single-walled carbon nanotubes

Abstract

In this study, we demonstrated the remarkable sensitivity to electrochemical local charge of sulfur chains encapsulated in small-diameter single-walled carbon nanotubes (S@SWCNTs). To perform micro- and macro-spectroscopic probing, a transparent electrochemical cell was designed in which the charging electrode is formed based on S@SWCNTs. During a short-term electrochemical charging, significant reversible changes were observed in-situ in both Raman and UV–vis-Nir spectra of S@SWCNTs. The optical response was found to depend on the magnitude and sign of the charge, as well as on the duration of the electrochemical charging process at a given potential. The enhanced Raman modes of sulfur chains exhibited a notable linear shift (up to 10 cm-1) accompanied by a redistribution of their intensities. A correlation is identified of the chronoamperometry curve (charging current versus time) and transformations of the Raman spectrum of single-atom sulfur chains. Atomistic simulations allowed to attribute these changes in the Raman spectrum to the softening of the sulfur bonds upon charging. Our findings revealed that the nanotube inhibits the chemical interactions between encapsulated sulfur and local charge sources, thus rendering S@SWCNTs suitable for repeated utilization in local charge analysis.