Toward High Conversion Efficiency of Thermoelectric Modules through Synergistical Optimization of Layered Materials

Making High Thermoelectric and Superior Mechanical Performance Nb0.88Hf0.12FeSb Half-Heusler via Additive Manufacturing

Thermoelectric generators held great promise through energy harvesting from waste heat. Their practical application, however, is greatly constrained by poor raw material utilization and tedious processing in fabricating desired shapes. Herein, a state-of-the-art process is reported for 3D printing the half-Heusler (Nb0.88Hf0.12FeSb) thermoelectric material using laser powder bed fusion (LPBF). The multi-dimensional intra- and inter-granular defects created by this process greatly suppress thermal conductivity by providing numerous phonon scattering centers. The resulting LPBF-fabricated half-Heusler exhibits a high figure of merit ≈1.2 at 923 K and a single-leg maximum efficiency of ≈3.3% at a temperature difference (ΔT) of 371 K. Hafnium oxide nanoparticles generated during LPBF effectively prevent crack propagation, ensuring competent mechanical performance and reliable thermoelectric output. The findings highlight the significant potential of LPBF in driving the next industrial revolution of highly efficient and customizable thermoelectric materials.

High-Performance AgSbTe2 Thermoelectrics: Advances, Challenges, and Perspectives

Environmental-friendless and high-performance thermoelectrics play a significant role in exploring sustainable clean energy. Among them, AgSbTe2 thermoelectrics, benefiting from the disorder in the cation sublattice and interface scattering from secondary phases of Ag2Te and Sb2Te3, exhibit low thermal conductivity and a maximum figure-of-merit ZT of 2.6 at 573 K via optimizing electrical properties and addressing phase transition issues. Therefore, AgSbTe2 shows considerable potential as a promising medium-temperature thermoelectric material. Additionally, with the increasing demands for device integration and portability in the information age, the research on flexible and wearable AgSbTe2 thermoelectrics aligns with contemporary development needs, leading to a growing number of research findings. This work provides a detailed and timely review of AgSbTe2-based thermoelectrics from materials to devices. Principles and performance optimization strategies are highlighted for the thermoelectric performance enhancement in AgSbTe2. The current challenges and future research directions of AgSbTe2-based thermoelectrics are pointed out. This review will guide the development of high-performance AgSbTe2-based thermoelectrics for practical applications.

Bi2Te3-Based Thermoelectric Modules for Efficient and Reliable Low-Grade Heat Recovery

Bismuth-telluride-based alloy has long been considered as the most promising candidate for low-grade waste heat power generation. However, optimizing the thermoelectric performance of n-type Bi2Te3 is more challenging than that of p-type counterparts due to its greater sensitivity to texture, and thus limits the advancement of thermoelectric modules. Herein, the thermoelectric performance of n-type Bi2Te3 is enhanced by incorporating a small amount of CuGaTe2, resulting in a peak ZT of 1.25 and a distinguished average ZT of 1.02 (300-500 K). The decomposed Cu+ strengthens interlayer interaction, while Ga+ optimizes carrier concentration within an appropriate range. Simultaneously, the emerged numerous defects, such as small-angle grain boundaries, twin boundaries, and dislocations, significantly suppresses the lattice thermal conductivity. Based on the size optimization by finite element modelling, the constructed thermoelectric module yields a high conversion efficiency of 6.9% and output power density of 0.31 W cm-2 under a temperature gradient of 200 K. Even more crucially, the efficiency and output power little loss after subjecting the module to 40 thermal cycles lasting for 6 days. This study demonstrates the efficient and reliable Bi2Te3-based thermoelectric modules for broad applications in low-grade heat harvest.

Tribovoltaic Effect: Origin, Interface, Characteristic, Mechanism & Application

Tribovoltaic effect is a phenomenon of the generation of direct voltage and current by the mechanical friction on semiconductor interface, which exhibits a brand-new energy conversion mechanism by the coupling of semiconductor and triboelectrification. Here, the origin, interfaces, characteristics, mechanism, coupling effect and application of the tribovoltaic effect is summarized and reviewed. The tribovoltaic effect is first proposed in 2019, which has developed in various forms tribovoltaic nanogenerator (TVNG) including metal-semiconductor, metal-insulator-semiconductor, semiconductor-semiconductor, liquid-solid and flexible interfaces. Compared with triboelectric nanogenerator, the TVNG has the characteristics of direct-current, high current density (mA-A cm-2) and low impedance (Ω-kΩ). The two mainstream views on the tribovoltaic generation mechanism, one dominated by built-in electric fields and the other dominated by interface electric fields, have been elaborated and summarized in detail. The tribo-photovoltaic effect and tribo-thermoelectric effect are also discovered and introduced because they can easily interact with other multi-physical field effects. The TVNGs are suitable for making energy harvesting and self-powered sensing devices for micro-nano energy applications. This paper not only revisit the development of the tribovoltaic effect, but also makes prospects for mechanism research, device fabrication and integrated application, which can accelerate the evolution of smart wearable electronics and intelligent industrial components.

Sustainable thermal energy harvest for generating electricity

Electricity is the lifeblood of modern society. However, the predominant source of electricity generation still relies on non-renewable fossil fuels, whose combustion releases greenhouse gases contributing to global warming. The increasing demand for energy and escalating environmental concerns necessitate proactive measures to develop innovative green energy technologies capable of both cooling the Earth and generating electricity. Here, we look forward to an interdisciplinary power system integrating solar absorbers, radiative coolers, and thermoelectric generators. This system can simultaneously harvest thermal energy from the sun and from cold space, thereby transforming the challenges posed by global warming into opportunities for the production of clean electricity. We underscore recent advancements in this field and address key challenges while also exploring forward-looking opportunities in the foreseeable future. The proposed integrated energy technology achieves uninterrupted power supply through the unrestricted capture of thermal energy, offering a robust alternative pathway for next-generation sustainable energy technologies.

Performance boost for bismuth telluride thermoelectric generator via barrier layer based on low Young's modulus and particle sliding

The lack of desirable diffusion barrier layers currently prohibits the long-term stable service of bismuth telluride thermoelectric devices in low-grade waste heat recovery. Here we propose a new design principle of barrier layers beyond the thermal expansion matching criterion. A titanium barrier layer with loose structure is optimized, in which the low Young's modulus and particle sliding synergistically alleviates interfacial stress, while the TiTe2 reactant enables metallurgical bonding and ohmic contact between the barrier layer and the thermoelectric material, leading to a desirable interface characterized by high-thermostability, high-strength, and low-resistivity. Highly competitive conversion efficiency of 6.2% and power density of 0.51 W cm-2 are achieved for a module with leg length of 2 mm at the hot-side temperature of 523 K, and no degradation is observed following operation for 360 h, a record for stable service at this temperature, paving the way for its application in low-grade waste heat recovery.

Selective Scatterings of Phonons and Electrons in Defective Half-Heusler Nb1- δ CoSb for the Figure of Merit zT > 1

The recently developed defective 19-electron half-Heusler (HH) compounds, represented by Nb1- δ CoSb, possess massive intrinsic vacancies at the cation site and thus intrinsically low lattice thermal conductivity that is desirable for thermoelectric (TE) applications. Yet the TE performance of defective HHs with a maximum figure of merit (zT) <1.0 is still inferior to that of the conventional 18-electron ones. Here, a peak zT exceeding unity is obtained at 1123 K for both Nb0.7 Ta0.13 CoSb and Nb0.6 Ta0.23 CoSb, a benchmark value for defective 19-electron HHs. The improved zT results from the achievement of selective scatterings of phonons and electrons in defective Nb0.83 CoSb, using lanthanide contraction as a design factor to select alloying elements that can strongly impede the phonon propagation but weakly disturb the periodic potential. Despite the massive vacancies induced strong point defect scattering of phonons in Nb0.83 CoSb, Ta alloying is still found effective in suppressing lattice thermal conductivity while maintaining the carrier mobility almost unchanged. In comparison, V alloying significantly deteriorates the carrier transport and thus the TE performance. These results enlarge the category of high-performance HH TE materials beyond the conventional 18-electron ones and highlight the effectiveness of selective scatterings of phonons and electrons in developing TE materials even with massive vacancies.