• Energy Research

AbstractThermoelectric materials are highly promising for waste heat harvesting. Although thermoelectric materials research has expanded over the years, bismuth telluride‐based alloys are still the best for near‐room‐temperature applications. In this work, a ≈38% enhancement of the average ZT (300−473 K) to 1.21 is achieved by mixing Bi0.4Sb1.6Te3 with an emerging thermoelectric material Sb2Si2Te6, which is significantly higher than that of most BiySb2−yTe3‐based composites. This enhancement is facilitated by the unique interface region between the Bi0.4Sb1.6Te3 matrix and Sb2Si2Te6‐based precipitates with an orderly atomic arrangement, which promotes the transport of charge carriers with minimal scattering, overcoming a common factor that is limiting ZT enhancement in such composites. At the same time, high‐density dislocations in the same region can effectively scatter the phonons, decoupling the electron‐phonon transport. This results in a ≈56% enhancement of the thermoelectric quality factor at 373 K, from 0.41 for the pristine sample to 0.64 for the composite sample. A single‐leg device is fabricated with a high efficiency of 5.4% at ΔT = 164 K further demonstrating the efficacy of the Sb2Si2Te6 compositing strategy and the importance of the precipitate‐matrix interface microstructure in improving the performance of materials for relatively low‐temperature applications.

The recent advances and new insights resulting thereof in applying defect engineering to improving the thermoelectric performance and mechanical properties of inorganic materials are reviewed.

Segmented cells enable real time visualization of the flow distribution in vanadium redox flow batteries by local current or voltage mapping. The lateral flow of current within thick porous electrodes, however, impairs the local resolution of the detected signals. In this study, the open circuit voltage immediately after the cessation of charge/discharge is used for the mapping of reactant conversion. This quantity is not hampered by lateral flow of current and can be conveniently transformed to the corresponding state of charge. The difference between theoretically calculated and experimentally determined conversion (change in the state of charge) across the electrode is used to determine local variations in conversion efficiency. The method is validated by systematic experiments using electrodes with different modifications, varying current densities and flow configurations. The procedure and the interpretation are simple and scalable to any size of flow cell.

Abstract Graphite felts are the most commonly used electrode materials in vanadium redox flow batteries. In the conventional cell design, flat sheets of graphite bipolar plates and porous graphite felts are stacked without any bonding, which requires a certain degree of compression to minimize the contact resistance. Excessive compression of the electrode, however, leads to non-uniform flow distribution and potential occurrence of zones with the retarded flow of electrolyte. This study investigates a wide range of electrode compressions and their effect on the cell performance. The results show that a compression of 25% is the optimal trade-off between contact resistance, homogeneity of flow distribution and pumping losses. Moreover, spatially resolved measurements using a segmented cell are employed to visualize the flow distribution across the electrode in real time. The open circuit voltage after the termination of the cell charge/discharge is converted to the corresponding state of charge (SOC) of the electrolyte, and the difference between the theoretical and experimental state of charge of electrolyte is used to quantify the flow distribution across the electrode. The results show that the optimum conversion of the reactant can be achieved during a single pass at 25% electrode compression. This method of segmentation is simple and scalable to any size of the battery.

The off-centered Ge leads to the ultralow lattice thermal conductivity and record high average ZT for n-type PbSe.

We improve n-type lead chalcogenides by adding GaSb to reduce lattice thermal conductivity and achieve conduction band convergence. This significantly enhances the thermoelectric performance of n-type PbS, making it comparable to its p-type counterpart.

Thermoelectric materials can be potentially employed in solid-state devices that harvest waste heat and convert it to electrical power, thereby improving the efficiency of fuel utilization. The spectacular increases in the efficiencies of these materials achieved over the past decade have raised expectations regarding the use of thermoelectric generators in various energy saving and energy management applications, especially at mid to high temperature (400-900 °C). However, several important issues that prevent successful thermoelectric generator commercialization remain unresolved, in good part because of the lack of a research roadmap.

Decades of studies on thermoelectric materials have enabled the design of high‐performance materials based on basic materials properties, such as bandgap engineering. In general, bandgap energies correspond to the temperature at which the peak thermoelectric performance occurs. For instance, CuGaTe2 with a relatively wide bandgap of 1.2 eV has its peak zT > 1 at > 900 K. On the other hand, the zT is usually very low (<0.1) for this material at room temperature. This severely limits its average zT and hence overall performance. In this study, a phase diagram‐guided Sb alloying strategy to improve the low‐temperature zT of CuGaTe2 is used, by leveraging on the solubility limits to control the formation of the microstructural defects. The addition of Sb simultaneously improves the electrical conductivity and decreases the lattice thermal conductivity. For a low‐temperature range of 300–623 K, this Sb‐alloying strategy enables the achievement of a record high average zT of 0.33. The strategy developed in this study targets the improvement of the low‐temperature range of CuGaTe2, which is rarely focused on for wide‐bandgap ABX2 compounds, opening up more opportunities for holistic performance improvements, potentially enabling ultrahigh‐performance thermoelectrics over a wide temperature range.