• Energy Research

Heusler compounds with semiconducting properties represent an important class of functional materials. Usually, research on these systems is guided by simple electron-counting rules, such as the Slater-Pauling principle. Here, we report on the discovery of Heusler-type semiconductors, significantly deviating from the Slater-Pauling rule. We theoretically predict the occurrence of nonmagnetic semiconducting ground states in various highly off-stoichiometric full-Heusler alloys, where self-substitution leads to a band-gap opening. This unexpected trend is confirmed experimentally by thermoelectric transport measurements on a multitude of Fe2−2xV1−xAl1+3x samples with up to 20% substitution of Fe and V atoms. The band-gap opening leads to an exceptionally large Seebeck coefficient in p-type Fe2VAl thermoelectrics, previously limited by bipolar conduction and low-density-of-states effective mass. Consequently, our work presents a paradigm to tune the band gap of Heusler compounds by self-substitution and introduces a hitherto unexplored class of semiconductors with exceptional thermoelectric properties, offering significant potential for advancements in energy science and sustainable-energy technologies. Published by the American Physical Society 2024

AbstractThe pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy‐efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, “soft chemistry” techniques such as solution‐based, solvothermal, microwave‐assisted, and mechanochemical (ball‐milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so‐produced and the prospects of developing such techniques further.

Magnesium ferrite MgFe2O4 was synthesized with two different methods, spark plasma sintering (SPS) and conventional solid-state reaction sintering (SSRS), and thermoelectric properties were investigated. SPS processing was found to yield two attractive features: SPS at 900 °C enabled retaining the submicron particle size of 0.3–0.5 µm from ball-milling, leading to lower thermal conductivity, 3 W/mK@300 K. 1200 °C SPS sintering led to the same sample grain size of 1.0–3.0 µm as SSRS, but still exhibited significantly lower thermal conductivity of 4.3 W/mK@300 K compared to the SSRS sample with 14 W/mK@300 K, which exhibited neck formation between particles. Furthermore, while the finer microstructuring led to a reduction in the thermal conductivity, the resistivity of SPS MgFe2O4 showed little dependence on the particle size at expected thermoelectric working temperatures above 523 K, which indicates success to some degree of phonon selective scattering due to differences in mean-free-paths of electrons and phonons. As a process, SPS samples are found to exhibit four- to sevenfold enhancement of ZT compared to the conventional SSRS sample. While the maximum ZT in the present samples is relatively low, taking a value of 0.07 for the SPS 1200 °C sintered sample, the processing insights may be utilized for similar systems.

AbstractAmbient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere.

Abstract The present work demonstrates a totally radical change in conduction nature from typical p-type to n-type through ionic transport in FeCl3 doped free-standing poly(3-hexylthiophene) (P3HT) films. The thermodiffusion of Cl− ions generated a giant negative Seebeck coefficient (∼2.7 mV/K) and a moderately high electrical conductivity (∼1 S/cm); an unprecedented level in polymers. A thermoelectric power generator fabricated using these P3HT films delivered an output electrical power of 25 μW with open circuit voltage of 128 mV for a ΔT of 46 °C. Though continuous operation reduced the output power due to inability of the ions to pass through the interface between doped P3HT and metallic contact, yet the generated voltage was found to be quite stable over a period of 1 h under load. With such a high n-type Seebeck coefficient, free-standing P3HT films show a great potential for energy harvesting from intermittent heat sources as well as in supercapacitor charging for futuristic energy storage devices.

An effective thermoelectricity–freshwater cogenerator using solar energy and scavenging energy has been proposed as a promising solution to water scarcity and electricity shortage.