Solution-Based Synthesis and Processing of Metal Chalcogenides for Thermoelectric Applications

Metal chalcogenide materials are current mainstream thermoelectric materials with high conversion efficiency. This review provides an overview of the scalable solution-based methods for controllable synthesis of various nanostructured and thin-film metal chalcogenides, as well as their properties for thermoelectric applications. Furthermore, the state-of-art ink-based processing method for fabrication of thermoelectric generators based on metal chalcogenides is briefly introduced. Finally, the perspective on this field with regard to material production and device development is also commented upon.

Molecular Dynamics Simulation of Bismuth Telluride Exfoliation Mechanisms in Different Ionic Liquid Solvents

Bismuth telluride (Bi₂Te₃) is a well-known thermoelectric material with potential applications in several different emerging technologies. The bulk structure is composed of stacks of quintuple sheets (with weak interactions between neighboring sheets), and the performance of the material can be significantly enhanced if exfoliated into two-dimensional nanosheets. In this study, eight different imidazolium-based ionic liquids are evaluated as solvents for the exfoliation and dispersion of Bi₂Te₃ at temperatures ranging from 350 to 550 K. Three distinct exfoliation mechanisms are evaluated (pulling, shearing, and peeling) using steered molecular dynamics simulations, and we predict that the peeling mechanism is thermodynamically the most favorable route. Furthermore, the [Tf₂N^-]-based ionic liquids are particularly effective at enhancing the exfoliation, and this performance can be correlated to the unique molecular-level solvation structures developed at the Bi₂Te₃ surfaces. This information helps provide insight into the molecular origins of exfoliation and solvation involving Bi₂Te₃ (and possibly other layered chalcogenide materials) and ionic liquid solvents.

Mechanism of bismuth telluride exfoliation in an ionic liquid solvent

Bismuth telluride (Bi2Te3) is a well-known thermoelectric material that has a layered crystal structure. Exfoliating Bi2Te3 to produce two-dimensional (2D) nanosheets is extremely important because the exfoliated nanosheets possess unique properties, which can potentially revolutionize several material technologies such as thermoelectrics, heterogeneous catalysts, and infrared detectors. In this work, ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) is used to exfoliate Bi2Te3 nanoplatelets. In both experiments and in molecular dynamics (MD) simulations, the Bi2Te3 nanoplatelets yield a stable dispersion of 2D nanosheets in the IL solvent, and our MD simulations provide molecular-level insight into the kinetics and thermodynamics of the exfoliation process. An analysis of the dynamics of Bi2Te3 during exfoliation indicates that the relative translation (sliding apart) of adjacent layers caused by IL-induced forces plays an important role in the process. Moreover, an evaluation of the MD trajectories and electrostatic interactions indicates that the [C4mim](+) cation is primarily responsible for initiating Bi2Te3 layer sliding and separation, while the Cl(-) anion is less active. Overall, our combined experimental and computational investigation highlights the effectiveness of IL-assisted exfoliation, and the underlying molecular-level insights should accelerate the development of future exfoliation techniques for producing 2D chalcogenide materials.