Thermal and kinetic studies of sulfur-rich molybdenum and tungsten polysulfides

• Published in: Journal of alloys and compounds 2021-01, Vol.851, p.156705, Article 156705
• Main Authors: Poltarak, Anastasiia A., Logvinenko, Vladimir A., Enyashin, Andrey N., Artemkina, Sofya B., Poltarak, Pavel A., Ivanova, Mariia N., Grayfer, Ekaterina D., Fedorov, Vladimir E.
• Format: Article
• Language: English
• Subjects: Amorphous materials; Chemical properties; Decomposition; Depolymerization; DFT calculations; Diffusion rate; Heating rate; Inert atmospheres; Inorganic materials; Kinetics; Molybdenum; Morphology; Nucleation; Polysulfides; Stability; Sulfur; Thermal analysis; Thermal decomposition; Thermogravimetric analysis; Transition metal chalcogenides; Transition metals; Tungsten
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.156705

Sulfur-rich transition metal polysulfides with multiple disulfide bonds (S–S) are a family of inorganic materials with unusual chemical properties and potential in catalysis and energy-related applications. In the current work, we present a kinetic study of the thermal decomposition of amorphous pentasulfides MoS5 and WS5 based on thermogravimetric analysis (TGA) in an inert atmosphere at various heating rates (10, 20, 30 °C/min). Thermal decomposition of both pentasulfides proceeds via a two-step, consecutive process. First, starting from ∼190 °C (M = Mo) or ∼240 °C (M = W) MS5 transform into intermediate products MS3, which then convert into MS2 at ∼380 °C (M = Mo) or 300 °C (M = W) (at the heating rate of 30 °C/min). The main kinetic parameters (activation energy, pre-exponential factor and reaction type) were calculated. Both steps are well described by the Avrami–Erofeev model, comprising random nucleation and subsequent nucleate growth. The rate-controlling step is diffusion, as spherical particle morphology of MoS5 and WS5 may slow down the elimination of sulfur produced during decomposition. The final decomposition products are weakly crystalline disulfides (MoS2, WS2), which inherit the spherical morphology of MoS5 (WS5). Theoretical calculations suggest that the very first step of the MS5 decomposition process is the depolymerization of MS5 chains into cluster fragments, rather than direct desulfurization. [Display omitted] •Amorphous sulfur-rich spherical particles of MoS5 and WS5 are prepared by a wet method.•MoS5 and WS5 thermally decompose to MoS2 (WS2) via a two-step, consecutive process.•Activation energy, pre-exponential factor and the reaction model were calculated.•Thermal decomposition follows the Avrami–Erofeev reaction mechanism.•DFT modeling reveals that the decomposition begins with the MoS5 (WS5) chain depolymerization.