Half-Heusler (HH) alloys have attracted considerable interest as promising thermoelectric (TE) materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties of HH alloys. Next, we review the details of HH nanocomposites as obtained by different techniques. Finally, the review closes by highlighting several promising strategies for further research directions in these very promising TE materials.

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Mixed ionic-electronic conducting (MIEC) membranes have gained growing interest recently for various promising environmental and energy applications, such as H 2 and O 2 production, CO 2 reduction, O 2 and H 2 separation, CO 2 separation, membrane reactors for production of chemicals, cathode development for solid oxide fuel cells, solar-driven evaporation and energy-saving regeneration as well as electrolyzer cells for powerto-X technologies. The purpose of this roadmap, written by international specialists in their fields, is to present a snapshot of the state-of-the-art, and provide opinions on the future challenges and opportunities in this complex multidisciplinary research field. As the fundamentals of using MIEC membranes for various applications become increasingly challenging tasks, particularly in view of the growing interdisciplinary nature of this field, a better understanding of the underlying physical and chemical processes is also crucial to enable the career advancement of the next generation of researchers. As an integrated and combined article, it is hoped that this roadmap, covering all these aspects, will be informative to support further progress in academics as well as in the industry-oriented research toward commercialization of MIEC membranes for different applications.

The air-stable phosphide, Ag6Ge10P12, was synthesized from its elements in gram amounts. As its structure is closely related to high-performance thermoelectric tetrahedrites (Ag6□Ge4Ge6P12 ≡ Cu6SSb4Cu6S12), we studied temperature dependent single-crystal X-ray diffraction experiments, quantum chemical calculations, and thermoelectric transport properties of spark plasma sintered and pristine, single crystalline samples, in order to give a comprehensive picture of its thermoelectric performance and its origin. The semiconducting character of this material is reflected in band structure calculations. Measurements of the thermal diffusivity exhibit a very low thermal conductivity, κ < 1 W m–1 K–1, which is close to a phonon glass-like behavior, and has its origin in a strong local bonding asymmetry, induced by strong bonding of the phosphorus–germanium (Ge4+) covalent framework and weak bonding of lone-pair electrons (Ge2+). This chemical bond hierarchy creates a pronounced anisotropic behavior of the silver atoms leading to low-frequency vibrations and thermal damping. Combining this with a moderate electrical resistivity (ρ ∼ 15 mΩ cm) and a high Seebeck coefficient (S ∼ 380 μV K–1) results in a remarkably high figure of merit (zT) of about 0.6 at 700 K. These results demonstrate that Ag6Ge10P12 is one of the best thermoelectric phosphides and a promising new platform for the future development of thermoelectrics.

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