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

TL;DR

This study investigates the oxidation processes of liquid-dispersed titanium (IV) sulphide (TiS₂) using in-situ and ex-situ TEM techniques, revealing how water and oxygen gas cause different oxidation behaviors relevant for energy storage applications.

Contribution

It provides detailed microscopic and spectroscopic insights into TiS₂ oxidation mechanisms under different conditions, combining experimental observations with thermodynamic calculations.

Findings

Water causes slow edge oxidation forming amorphous oxide.

Oxygen gas rapidly oxidizes entire flakes to polycrystalline oxide at high temperatures.

Oxidisation by water and oxygen is thermodynamically favorable according to DFT calculations.

Abstract

The degradation of liquid dispersed titanium (IV) sulphide (TiS$_2$) is studied from the point of view of oxidisation. TiS$_2$ is a layered two-dimensional nanomaterial, with potential for energy storage applications. However, flakes in dispersion were observed to degrade. We examined two oxidisation routes: deionised water at room temperature and oxygen gas within the temperature range 150-350{\deg}C. Water was seen to slowly oxidise flakes inwards from the edge, forming an amorphous oxide, a result comparable to the state of flakes which degraded within the original dispersion. Oxygen gas was seen to rapidly oxidise entire flakes to a polycrystalline oxide, when heated 275 {\deg}C and above. Degradation was studied with scanning transmission electron microscopy (STEM), energy dispersed x-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS). Density Functional Theory calculations have shown oxidisation by both water and gas molecules to be thermodynamically favourable.