Rafiq Mulla

Thermoelectric materials enable the direct conversion of heat into electricity and offer attractive solutions for energy harvesting and waste-heat recovery. Their performance is evaluated by the dimensionless figure of merit, ZT = S ² σT / κ , where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. Traditionally, high ZT values have been achieved at elevated temperatures in materials such as PbTe, SiGe, half-Heusler compounds, skutterudites, and metal oxides. However, for emerging applications including consumer electronics, wearable devices, Internet-of-Things systems, and biomedical devices/sensors, achieving high ZT at/near room temperature is essential. In recent years, significant progress has been made towards this goal through strategies such as nanostructuring, band-structure engineering, defect/interface engineering, and also by the discovery of novel thermoelectric compounds. These advances have enabled several material systems to reach ZT values of more than 1 under ambient conditions. This review provides a comprehensive overview of recent developments in room-temperature thermoelectric materials, with a particular focus on high-ZT reports.

In this study, a novel approach is presented in which bismuth is coated onto cotton wool fibers using sputter deposition, followed by mechanical pressing to form compact pellets. Despite the inherently low density and porous nature of the material, the resulting composite pellets exhibit Seebeck coefficients comparable to that of bulk bismuth. An enhanced thermal gradient is observed across the pellet, attributed to reduced thermal transport arising from the fibrous and porous structure. Although a reduction in electrical conductivity is noted, the present strategy suggests promising potential for lightweight and flexible thermoelectric applications. This work highlights the feasibility of using low-cost, biodegradable substrates for improving thermal gradients in waste heat recovery systems.

In this paper, a simple floating thermoelectric generator is presented that can utilize environmental heat and solar energy to generate electric power. A novel boat-like floating thermoelectric generator has been designed and fabricated using bismuth thin films. Electric potential is generated by directing solar radiation onto the top side of the generator, while the bottom of the thermoelectric boat is cooled by the surrounding water or heated by hot water on which it floats. Experimental observations demonstrate that the proposed generator, with 18 pairs of thermoelectric films, is capable of producing a voltage of 19.1 mV and a power output of 21.5 nW at a heating temperature of 50 °C.

PEDOT:PSS is one of the most researched polymers for thermoelectrics due to its solution-processability, flexibility, and high electrical conductivity. This highlight discusses recent strategies reported on PEDOT:PSS based thermoelectric materials.

Transparent thermoelectric materials are a special kind of material that converts thermal energy into electrical power and possess unique properties for transparent electronics and future energy applications. These materials are being studied for specific applications such as windowpanes, photovoltaic panels, sensor displays, smart electronic devices, and more. For such applications, it is desirable that the thermoelectric materials be in the form of thin films or coatings, be optically transparent, and exhibit excellent thermoelectric performance. Understanding the electrical, thermal, and optical properties of materials is crucial for the development of transparent thermoelectric devices. This paper discusses the current progress in the development of transparent thermoelectric materials.

The inherent low thermal conductivity, low cost, and flexibility of polymeric materials make them potential candidates for thermoelectric applications. Their eco-friendliness and mechanical flexibility are useful for the design of portable and flexible self-powered electronics. However, the heat-to-electrical power conversion efficiency, also known as the figure-of-merit (ZT), of polymer TE materials is low. Research efforts are in progress to enhance the thermoelectric performance of polymers and to find new kinds of polymer composites. Recent research innovations, such as chemical doping of polymers, development of nanocomposites and hybrid composites, and nanostructuring have significantly changed the thermoelectric properties of the polymeric materials. In this article, we summarize the recent developments and achievements in polymer materials for thermoelectric applications.

A simple do-it-yourself (DIY) apparatus is designed and built for the measurement of the electrical resistivity of materials. The tool is portable and easy to operate, and students/new researchers can build their own apparatus with a minimum amount of time and raw materials. The apparatus’ spring-loaded four-point probes help provide a good electrical contact between the sample surface and the probes. It has been checked for its reliability by comparing the resistivity data with literature values and the measurements match well with the previous data. The apparatus is suitable for measurements from room temperature to ∼100 °C.

Electrically highly conducting CuS particles were encapsulated within a compound with a high Seebeck coefficient, i.e. CuI, to form core–shell type composites. As a result, an improved zT of 0.46 at room temperature has been achieved.

This article highlights new and interesting research ideas that explored graphene's potential for thermoelectrics.