Ubiquitous trisulfur radical anion: fundamentals and applications in materials science, electrochemistry, analytical chemistry and geochemistry

Abstract

The trisulfur radical anion [S3]˙(-) is well-known from inorganic chemistry textbooks as the blue chromophore in ultramarine blues in which this highly reactive species is trapped in a zeolitic framework. Recent findings have revealed that [S3]˙(-) has a multi-faceted role in a variety of media, including alkali metal-sulfur batteries, aqueous solutions at high temperatures and pressures, and ionic liquids; it has also been used to detect trace amounts of water in organic solvents. This tutorial review illustrates how various physical techniques are used to identify a reactive species in solution and shows how elucidation of electronic structures can be used to explain spectroscopic and structural properties. Examples of the function of [S3]˙(-) in materials science, electrochemistry, analytical chemistry and geochemistry are used to illustrate the widespread influence of this fundamentally important triatomic sulfur species.

Surface-enhanced redox chemistry of polysulphides on a metallic and polar host for lithium-sulphur batteries

“…This can be explained by the fact that where little or no interaction of LiPSs with support is present-as in the case of VC and graphite-the polysulphide species exist in rapid equilibria in solution. Disproportionation of intermediate-length LiPSs such as S 4 2 À to sulphur with lower and higher oxidation states is known to occur under these conditions 38,39 . Shifting of the equilibrium towards elemental sulphur formation is driven both by its insolubility and strong interaction with the carbon surface, thus accounting for the C-S 0 contribution.…”

“…Initial reduction is thought to give S 8 2 À that disproportionates in solution to elemental sulphur and S 6 2 À (refs 31,38,39). The soluble S 6 2 À can either undergo cleavage to form soluble, reducible S 3 À ; or further reduce to S 4 2 À and ultimately precipitate Li 2 S; and/or reduce and disproportionate to form a higher order polysulphide and Li 2 S. These solution-mediated reactions are highly complex 38,39 . Nonetheless, data clearly show the high concentration or supersaturation of LiPS before the end of discharge (Fig.…”

X-ray spectroscopy as a probe for lithium polysulfide radicals

“…We will pay particular attention to the ''ubiquitous'' 34 trisulfur molecule, as this species is most often postulated as being present in large quantities in working Li-S electrochemical cells. The objective here is to start with the smallest polysulfide molecule, disulfur (S 2 ), in various charge states, and demonstrate how one would expect the XAS peak positions and intensities to change, based on a simple molecular orbital (MO) analysis.…”

Transport Properties of Polysulfide Species in Lithium–Sulfur Battery Electrolytes: Coupling of Experiment and Theory

“…This gives rise to the characteristic deep blue color of such solutions. 22,23 However, cleavage in DOL/DME is not favored at room temperature, and hence the concentration of the trisulfide radical is neglible. 24,25 Despite these many experimental studies to elucidate polysulfide speciation, very limited modeling work on Li–S batteries has been conducted that could provide an understanding of polysulfide transport properties, and hence their behavior in the cell.…”