An in situ and ex situ TEM study into the oxidation of titanium (IV) sulphide

Abstract

Titanium (IV) sulphide (TiS 2 ) is a layered transition metal dichalcogenide, which we exfoliate using liquid phase exfoliation. TiS 2 is a candidate for being part of a range of future technologies. These applications are varied, and include supercapacitor and battery energy storage devices, catalytic substrates and the splitting of water. The driving force behind our interest was as a material for energy storage devices. Here we investigate a potential failure mechanism for such devices, namely oxidation and subsequent loss of sulphur. This degradation is important to understand, since these applications are highly property-dependent, and changes to the chemistry will result in changes in desired properties. Two approaches to study oxidisation were taken: ex situ oxidation by water and oxygen at room temperature and in situ oxidation by a 5% O 2 /Ar gas at elevated temperatures. Both sources of oxygen resulted in oxidation of the starting TiS 2 flakes, with differing morphologies. Water produced amorphous oxide slowly growing in from the edge of the flakes. Oxygen gas at ≥375°C produced crystalline oxide, with a range of structures due to oxidation initiating from various regions of the observed flakes. npj 2D Materials and Applications (2017) 1:22 ; doi:10.1038/s41699-017-0024-4 INTRODUCTION Titanium (IV) sulphide, TiS 2 , is a candidate for applications in a range of future technologies, including catalytic substrates and the splitting of water, supercapacitors and energy storage devices. TiS 2 is a layered transition metal dichalcogenide (TMD) with hexagonal crystal symmetry and takes the 1T phase and is relatively under explored in two-dimensional form. Each layer consists of three sheets of atoms: the two outer planes are sulphur, coordinated to three titanium atoms with a trigonal pyramidal geometry; the middle plane is titanium and each atom takes octahedral coordination to six sulphur atoms. These atomic sheets are stacked ABC (Supplemental Information Fig. 1), while the layers themselves stack AA in the 1T phase.The excellent capacitive properties of bulk TiS 2 (high energydensity and power-density 1, 2 and excellent electronic conductivity 3 ) have attracted interest since the 1970s, with bulk TiS 2 used as a cathode material in lithium-metal/alloy anode batteries, where lithium metal ions were intercalated, transferring charge to reduce titanium 3d orbitals and causing reduction from Ti 4+ to Ti 3+ (refs. 4, 5). High rates of charging and discharging were demonstrated with near-perfect reversibility. In addition, the material forms a single phase with lithium (Li x TiS 2 ) over the entirety of the range 0 ≤ x ≤ 1, avoiding the need for phase changes upon (de-) lithiation which removes much of the strain induced in cycling, prolonging battery life. However, TMD/Lithium-metal batteries were withdrawn from consumers due to accidents in 1989 where the metallic lithium caught fire as a consequence of shortcircuiting due to lithium-dendrite growth.

In Situ Characterization of Transformations in Nanoscale Layered Metal Chalcogenide Materials: A Review

“…MCs can exhibit multiple polymorphs ( e. g ., the 2H, 1T, and 3R phases of MoS 2 ) [76] and stoichiometric variants ( e. g ., PtSe 2 and PtSe), [77] and transformations between these phases can occur under various conditions. Furthermore, MCs can contain defects (vacancies, dislocations, and grain boundaries), [78] and they may readily react with environmental species to form oxides [79] or oxychalcogenides [30] . In situ experimental techniques are critical for measuring changes in material structure and chemistry under exposure to different chemical or thermal conditions.…”

An Innovative Process for Production of Ti Metal Powder via TiSx from TiN

“…Oxygen contamination might come from insufficient drying process due to the strong hygroscopic properties of CaCl2. [22,39] The residual oxygen may be reduced in a longer electrolysis time because of the slow diffusion of oxygen in solid. Besides, Noguchi et al [22] also investigated the effect of dehydration on the residual oxygen contents of the samples, and they showed that Ti powder with 0.42 mass% O could be obtained from CaTiO3 at Q/Q0 = 600%.…”

Gentle transfer method for water- and acid/alkali-sensitive 2D materials for (S)TEM study

“…22 However, bulk TiS 2 is also well-known to be unstable in ambient conditions, not to mention its monolayer form, which would be quickly oxidized presumably due to the oxygen and water vapor in the air. 7,23 In order to fully develop the potential use of TiS 2 for any single-layer device, transferring the intact quality of 2D crystal and direct observing its pristine lattice structure without oxidation are prerequisite.…”