Turning heat into electricity: the challenge of designing an efficient and sustainable device

_{In the front row, from left to right: Marc Salleras, Joaquín Santander, and Marc Aceituno. In the second row: Alex Rodriguez Iglesias, Llibertat Abad, Luis Fonseca, and Iñigo Martin.}

Thermoelectric generators are capable of converting temperature differences into electrical energy. While they are a useful alternative for power generation in low-power devices, their manufacture relies on critical raw materials that are considered unsustainable. That is why a team at the CSIC’s Institute of Microelectronics of Barcelona (IMB-CNM-CSIC) is exploring new materials for manufacturing generators that are sustainable at every stage of the process.

Harnessing waste heat from the environment is useful for avoiding the use of batteries to power low-power sensors, such as those in the Internet of Things (IoT). They are also currently used in places where waste heat is abundant but changing batteries is difficult —in hard-to-reach or harsh environments, such as industrial reactors, power plants, engines, volcanoes, or even space missions.

Thermoelectric microgenerators are manufactured using micro and nanotechnologies, primarily with semiconductors. The main component of the device is the thermoelectric material, in which heat is converted into electricity; to do so, it must possess suitable thermal and electrical properties. However, the thermoelectric materials commonly used in their manufacture (based on bismuth and tellurium) are scarce, toxic, and difficult to integrate into miniaturized systems.

Now, a study published in Science and Technology of Advanced Materials presents a prototype thermoelectric microgenerator based on a sustainable material.

“We address two challenges: sustainability and performance. On the one hand, we propose replacing conventional thermoelectric materials with more sustainable alternatives. On the other hand, we demonstrate that optimizing heat management at the device architecture level is just as important as improving the material itself,” explains Marc Salleras, a researcher at IMB-CNM-CSIC and the study’s lead author.

An active material to conduct heat

The new microgenerator was developed in the Micro and Nanofabrication Clean Room at the IMB-CNM-CSIC, a Unique Science and Technology Infrastructure (ICTS) that is the one of a kind in Spain for the creation of silicon-based chips and systems. As with all devices of this type, the process involves layering materials “one layer at a time.” In this case, silicon, silicon oxide, silicon nitride, and metals (titanium and tungsten)—which are standard in the microelectronics industry—were used; the novelty lies in the "active material."

"In collaboration with the Danish DTU, we have integrated thin layers of a thermoelectric oxide, niobium-doped strontium titanate (Nb:STO), which is abundant, sustainable, and low in toxicity," says Joaquín Santander, a researcher at IMB-CNM-CSIC and the study’s first author. Furthermore, "we have implemented an innovative thermal management system using microadapters and heat sinks that significantly improves the useful thermal gradient (by a factor of 100)," he adds.

But how is this new material integrated? “Through silicon micromachining," adds Santander. “This allows us to create a membrane in the center of the silicon chip that remains suspended, and the thermoelectric material is placed on top of it," he explains.

This design forms the core of the device, allowing a temperature difference to develop between the hotter outer edge of the membrane and its cooler center when the platform is placed on a hot surface, such as at 175 °C (the highest temperature to which the device was subjected in this study).

“Heat flows from one side to the other through the thermoelectric material, converting it into electricity. In addition, a heat sink is attached to the center of the membrane, which allows for a much greater thermal gradient, drastically multiplying the energy extracted,” explains researcher Llibertat Abad, also an author of the publication.

The research continues: next steps

The developed system is highly versatile and can serve as a “test platform” for evaluating almost any thermoelectric material under real-world conditions. “It allows us to measure the material’s thermoelectric properties and, in turn, study its performance when integrated into a device—both under test conditions, by imposing a known temperature difference, and under operating conditions using a heat source,” says Marc Aceituno, a predoctoral researcher at the IMB-CNM. In the medium term, this “will accelerate the development of autonomous and sustainable power sources for IoT electronics.”

The current limitation is that the active material is polycrystalline in nature, so its electrical conductivity is lower than expected, which limits the power output. At the same time, although the heat sink has made it possible to overcome thermal barriers in this type of architecture—which previously limited the utilization of the ambient temperature gradient to only a small fraction of its potential—“its design and integration must be improved to eliminate the parasitic heat losses detected,” he concludes.

The team is already working on improving the device’s performance. In the case of niobium-doped strontium titanate, it has been found that improving its crystalline quality increases its electrical conductivity. In addition, collaborations have been initiated with other research groups to integrate new materials with potential into thermoelectric platforms.

The publication is authored by the aforementioned Salleras, Santander, Abad, and Aceituno; along with IMB-CNM researchers Iñigo Martin-Fernandez, Carlos Carbonell (currently at Glaucus Technology, United States), Alex Rodríguez-Iglesias, Laura Fuentes-Rodríguez (currently a research lecturer at the Universitat Rovira i Virgili), Marta Fernández-Regúlez, and Luis Fonseca. Also included are Aitor F. Lopeandia, from the Autonomous University of Barcelona (UAB) and the Catalan Institute of Nanoscience and Nanotechnology (ICN2); and Arindom Chatterjee and Nini Pryds, from the  Technical University of Denmark (DTU Energy).

_{Reference article: Santander, J., Martin-Fernandez, I., Carbonell, C., Rodríguez-Iglesias, A., Fuentes-Rodríguez, L., Fernández-Regúlez, M., … Salleras, M. (2026). A novel approach to micro-fabricated thermoelectric generators with SrTiO3. Science and Technology of Advanced Materials, 27(1). https://doi.org/10.1080/14686996.2026.2665920}