thermal treatments and consolidation of cdse&#45;snse particles to produce nanocomposites

Production of CdSe&amp;#45;SnSe Nanocomposites from Consolidated SnSe Particles

Thermoelectric (TE) materials, which convert heat into electricity and vice versa, can play an important role in sustainable energy management1. However, the low conversion efficiencies combined with the relatively high production costs of these materials have limited their broad application for industrial and domestic use. To overcome present challenges, cost-effective synthetic methods and the use of abundant and non-toxic materials with significantly improved efficiency must be implemented.
The thermoelectric figure of merit zT= S2&#963;T/&#954;, where S is the Seebeck coefficient, &#963; the electrical conductivity, T the absolute temperature, and &#954; the thermal conductivity, determines the efficiency of these materials. Due to the strong coupling of these properties, maximizing zT is a challenge. It often entails tuning the electronic band structure and microstructural defects to control charge and phonon scattering mechanisms2,3,4,5.
In the last decade, tin selenide (SnSe) has been explored as a non-toxic thermoelectric material due to its outstanding performance in its single crystal form (zT: p-type ~2.6, n-type ~2.8)6,7. However, single crystals are expensive to produce, limiting their applicability to devices. Alternatively, polycrystalline SnSe is cheaper to produce and mechanically more stable. The problem is that attaining high performance presents difficulties due to partial loss of anisotropy, diminishing electrical conductivity, greater ease of oxidation, and imprecise control of the doping level8,9,10.
Polycrystalline inorganic TE materials are usually processed in two steps: preparation of the semiconductor in powder form followed by consolidation of the powder into a dense pellet. Powders can be prepared through high-temperature reactions and grinding or directly by ball-milling11,12,13,14,15,16. Alternatively, powders can be synthesized via solution methods (e.g., hydrothermal, solvothermal, aqueous synthesis), requiring less demanding conditions (i.e., lower reagent purity, lower temperatures, and shorter reaction times)17,18,19,20,21.
This paper describes a method to produce dense SnSe nanocomposites from surface-modified SnSe particles that are synthesized in water. The process commences from the aqueous synthesis of SnSe particles, where reducing agents and bases are used to solubilize the Se and Sn reagents, respectively. When the solutions are combined, SnSe particles immediately start precipitating. After purification, SnSe particles are then functionalized with CdSe molecular complexes. During the annealing process, the molecular complexes decompose; forming CdSe nanoparticles19. The presence of CdSe nanoparticles inhibits grain growth and promotes the formation of many defects at varying length scales. These scattering sources result in low thermal conductivity and a high thermoelectric figure of merit22.

Author Spotlight: Advancing Energy Solutions Using Nanocomposites as Processed Thermoelectric Materials

Solution&#45;Processed, Surface&#45;Engineered, Polycrystalline CdSe&#45;SnSe Exhibiting Low Thermal Conductivity

Our group focused on developing materials for energy-related applications, emphasizing energy storage and thermal electricity. We used nano crystals as building blocks, or precursors for constructing the microscopic materials. And we investigate the transformation the nano crystals undergo into whole solids, aiming to enhance performance, and by understanding and controlling the properties derived from the nanoscale features.In particular, for thermal electric materials, we focused on defect control. Developing thermoelectric materials via solution processing involves numerous challenges. One, mitigating oxidation due to the nanoparticles'high surface to volume ratio.Reproducibility, due to the complexity of the process. And three, dealing with volatile species to ensure stability. Addressing and understanding these challenges is crucial for enhancing thermal electric materials efficiency for practical applications.Our research advanced cost-effective solution-processed thermal electric materials, by fine-tuning nanoparticle properties and their organization. We are uncovering the chemistry involved in the whole process, from the nanoparticle synthesis to the final consolidation. And currently, we are focused on how surface species or affect materials microstructure, and hence their performance.We enhanced thermoelectric performance through the utilizing solution process surface engineered particles, significantly reducing the thermal conductivity by micro structural tuning and the introduction of defects. This approach also is advantageous, because it uses inexpensive precursors, low temperatures, and also, we use water as a solvent. We found that certain molecules absorb at the particle surface and restrict grain growth.Now, we are trying to rationalize how different surface species affect microstructure and hence transport properties, based on their composition, chemical instability, and bonding nature.

Thermal Treatments and Consolidation of CdSe&#45;SnSe Particles to Produce Nanocomposites

thermal-treatments-consolidation-cdsesnse-particles-to-produce

Research

JoVE Journal

Chemistry

366 Views.  Institute of Science and Technology Austria (ISTA). Thermal Treatments and Consolidation of CdSe-SnSe Particles to Produce Nanocomposites

Video: Thermal Treatments and Consolidation of CdSe-SnSe Particles to Produce Nanocomposites

In recent years, solution processes have gained considerable traction as a cost-effective and scalable method to produce high-performance thermoelectric materials. The process entails a series of critical steps: synthesis, purification, thermal treatments, and consolidation, each playing a pivotal role in determining performance, stability, and reproducibility. We have noticed a need for more comprehensive details for each of the described steps in most published works. Recognizing the significance of detailed synthetic protocols, we describe here the approach used to synthesize and characterize one of the highest-performing polycrystalline p-type SnSe. In particular, we report the synthesis of SnSe particles in water and the subsequent surface treatment with CdSe molecular complexes that yields CdSe-SnSe nanocomposites upon consolidation. Moreover, the surface treatment inhibits grain growth through Zenner pinning of secondary phase CdSe nanoparticles and enhances defect formation at different length scales. The enhanced complexity in the CdSe-SnSe nanocomposite microstructure with respect to SnSe promotes phonon scattering and thereby significantly reduces the thermal conductivity. Such surface engineering provides opportunities in solution processing for introducing and controlling defects, making it possible to optimize the transport properties and attain a high thermoelectric figure of merit.

CdSe-SnSe nanocomposites are produced by consolidating surface-engineered SnSe particles. A simple aqueous synthesis is employed to produce SnSe particles. Coating SnSe particles with CdSe molecular complexes allows for controlling grain size and increasing the number of defects present in the nanocomposite, thus lowering the thermal conductivity.

In recent years, solution processes have gained considerable traction as a cost-effective and scalable method to produce high-performance thermoelectric ...