thermoelectric generators

INVITED REVIEW: Micro and Nano-Engineering Enabled New Generation of Thermoelectric Generator Devices and Applications

As we are advancing our world to smart living, a critical challenge is increasingly pressing - increased energy demand. While we need mega power supplies for running data centers and other emerging applications, we also need instant small-scale power supply for trillions of electronics that we are using and will use in the age of Internet of Things (IoT) and Internet of Everything (IoE). Such power supplies must meet some parallel demands: sufficient energy supply in reliable, safe and affordable manner. In that regard, thermoelectric generators emerge as important renewable energy source with great potential to take advantage of the widely-abundant and normally-wasted thermal energy. Thanks to the advancements of nano-engineered materials, thermoelectric generators’ (TEG) performance and feasibility are gradually improving. However, still innovative engineering solutions are scarce to sufficiently take the TEG performance and functionalities beyond the status-quo. Opportunities exist to integrate them with emerging fields and technologies such as wearable electronics, bio-integrated systems, cybernetics and others. This review will mainly focus on unorthodox but effective engineering solutions to notch up the overall performance of TEGs and broadening their application base. First, nanotechnology's influence in TEGs’ development will be introduced, followed by a discussion on how the introduction of mechanically reconfigurable devices can shape up the emerging spectrum of novel TEG technologies.

J. P. Rojas, D. Singh, S. Inayat, G. A. Torres Sevilla, H. M. Fahad, M. M. Hussain

J. Solid State Sci. Technol.2017 volume 6, issue 3, N3036-N3044

doi: 10.1149/2.0081703jssECS

Stress enabled transformation of ultra-thin 2D thermoelectric materials into 3D tubular thermoelectric generators

Thermoelectric generators (TEGs) are interesting energy harvesters from otherwise wasted heat. Here we show, a polymer assisted generic process and its mechanics to obtain sputtered thermoelectric (TE) telluride materials based 3D tubular structures with unprecedented length (up to seamless 4 cm and further expandable). This length allows for large temperature differences between the hot and cold ends, a critical but untapped enabler for high power generation. Compared to flat slab, better area efficiency has observed for rolled tube and compared to a solid rod architecture, a rolled tube uses less material (thus making it lightweight and cost effective) and has competitive performance advantage due to lesser contact area. We also show tubular architecture thermopile based TEG is able to achieve a generated power up to 5 µW (8 pairs of p- and n-type thermopiles) through temperature difference of 60 ᴼC. Demonstrated process can play important role to transform 2D atomic crystal structure TE materials into 3D tubular thermopiles for effective TEG application which can maintain higher temperature difference by longer distance between hot and cold end.

D. Singh, A. T. Kutbee, M. T. Ghoneim, A. M. Hussain, M. M. Hussain, Adv. Mater. Technol. 2017, 1700192.

Paper-based origami flexible and foldable thermoelectric nanogenerator

Paper has been an essential material in our daily life since ancient times. Its affordability, accessibility, adaptability, workability and its easiness of usage makes it an attractive structural material to develop many kind of technologies such as flexible electronics, and energy storage and harvesting devices. Additionally, the scientific community has increased its interest on waste heat as an environmentally friendly energy source to support the increasing energy demand. Therefore, in this paper we described two affordable and flexible thermoelectric nanogenerators (TEGs) developed on paper substrates by the usage of simple micromachining and microfabrication techniques. Moreover, they exhibit mechanical stability and adaptability (through folding and cutting techniques) for a diverse set of scenarios where vertical or horizontal schemes can be conveniently used depending on the final application. The first TEG device, implemented on standard paper, generated a power of 0.5 nW (ΔT=50 K). By changing the substrate to a tearless and extra-smooth polyester paper, the TEG performance was optimized achieving less internal resistance and a greater power of ~80 nW (ΔT=75 K), at the cost of more rigidity in the substrate. This power represented over three times higher power production than the standard paper–based TEG with same dimensions, number of thermoelectric pairs and temperature difference. Another interesting aspect of paper based TEG is due to its foldability, one can control the temperature difference by unfolding (larger separation between hot and cold ends) and folding (smaller separation). Finally, one of the underlying objectives of this work is to spread the availability of essential technologies to the broad population by inclusion of everyday materials and simple processes.

J. P. Rojas, D. Conchouso, A. Arevalo, D. Singh, I. G. Foulds, M. M. Hussain

Nano Energy Vol. 31, Jan 2017, Pages 296-301

Stretchable helical architecture inorganic-organic hetero thermoelectric generator

To achieve higher power output from a thermoelectric generator (TEG), one needs to maintain a larger temperature difference between hot and cold end. In that regard, a stretchable TEG can be interesting to adaptively control the temperature difference. Here we show, the development of simple yet versatile and highly stretchable thermoelectric generators (TEGs), by combining well-known inorganic thermoelectric materials Bismuth Telluride and Antimony Telluride (Bi2Te3 and Sb2Te3) with organic substrates (Off-Stoichiometry Thiol-Enes polymer platform – OSTE, polyimide or paper) and novel helical architecture (double-arm spiral/helix) to achieve over 100% stretchability. First, an OSTE-based TEG design demonstrates higher open circuit voltage generation at 100% strain than at rest, although it exhibits high internal resistance and a relatively complex fabrication process. The second, simpler TEG design, achieves a significant resistance reduction and two different structural substrates (PI and paper) are compared. The paper-based TEG generates 17 nW (ΔT=75 °C) at 60% strain, which represents more than twice the power generation while at rest (zero strain). On the other hand, polyimide produces more conductive TE films and higher power (~35 nW at ΔT=75 °C) but due to its higher thermal conductivity, power does not increase at stretch. In conclusion, highly stretchable TEGs can lead to higher temperature gradients (thus higher power generation), given that thermal conductivity of the structural material is low enough. Furthermore, either horizontal or vertical displacement can be achieved with double-arm helical architecture, hence allowing to extend the device to any nearby and mobile heat sink for continuous, effectively higher power generation.

J. P. Rojas, D. Singh, D. Conchouso, A. Arevalo, I. G. Foulds, M. M. Hussain

Nano Energy Vol. 30, Pages 691-699, Dec 2016

CMOS technology enabled flexible silicon based thermoelectric generators with improved performance

Flexible and semi-transparent high performance thermoelectric energy harvesters are fabricated on low cost bulk mono-crystalline silicon (100) wafers. The released silicon is only 3.6% as thick as bulk silicon reducing the thermal loss significantly and generating nearly 30% more output power than unpeeled harvesters. This generic batch processing is a pragmatic way of transforming traditional silicon circuitry for extremely deformable high-performance integrated electronics.

Sevilla, G. A. T., Inayat, S. B., Rojas, J. P., Hussain, A. M. and Hussain, M. M. (2013), Flexible and Semi-Transparent Thermoelectric Energy Harvesters from Low Cost Bulk Silicon (100). Small, 9: 3916–3921. doi:10.1002/smll.201301025

Power generation from thermoelectric system-embedded Plexiglas for green building technology

Thermoelectric materials embedded through or inside exterior glass windows can act as a viable source of supplemental power in geographic locations where hot weather dominates. This thermoelectricity is generated because of the thermal difference between the high temperature outside and the relatively cold temperature inside. Using physical vapor deposition process, we experimentally verify this concept by embedding bismuth telluride and antimony telluride through the 5 mm Plexiglas to demonstrate 10 nW of thermopower generation with a temperature gradient of 21 °C. Albeit tiny at this point with non-optimized design and development, this concept can be extended for relatively large-scale power generation as an additional power supply for green building technology.

Inayat, S.B. & Hussain, M.M. Appl Nanosci (2013) 3: 335.

Thermoelectricity from wasted heat of integrated circuits

We demonstrate that waste heat from integrated circuits especially computer microprocessors can be recycled as valuable electricity to power up a portion of the circuitry or other important accessories such as on-chip cooling modules, etc. This gives a positive spin to a negative effect of ever increasing heat dissipation associated with increased power consumption aligned with shrinking down trend of transistor dimension. This concept can also be used as an important vehicle for self-powered systems-on-chip. We provide theoretical analysis supported by simulation data followed by experimental verification of on-chip thermoelectricity generation from dissipated (otherwise wasted) heat of a microprocessor.

Fahad, H., Hasan, M., Li, G. et al. Appl Nanosci (2013) 3: 175.

Nano-materials Enabled Thermoelectricity from Window Glasses

With a projection of nearly doubling up the world population by 2050, we need wide variety of renewable and clean energy sources to meet the increased energy demand. Solar energy is considered as the leading promising alternate energy source with the pertinent challenge of off sunshine period and uneven worldwide distribution of usable sun light. Although thermoelectricity is considered as a reasonable renewable energy from wasted heat, its mass scale usage is yet to be developed. Here we show, large scale integration of nano-manufactured pellets of thermoelectric nano-materials, embedded into window glasses to generate thermoelectricity using the temperature difference between hot outside and cool inside. For the first time, this work offers an opportunity to potentially generate 304 watts of usable power from 9 m^2 window at a 20°C temperature gradient. If a natural temperature gradient exists, this can serve as a sustainable energy source for green building technology.

S. B. Inayat, K. R. Rader, M. M. Hussain

Scientific Reports 2, Article number: 841 (2012) doi:10.1038/srep00841

Acetic acid-confined synthesis of uniform three-dimensional (3D) bismuth telluride nanocrystalsconsisting of few-quintuple-layer nanoplatelets

High-selectivity, uniform three-dimensional (3D) flower-like bismuth telluride nanocrystals consisting of few-quintuple-layer nanoplatelets with a thickness down to 4.5 nm were synthesized for the first time by a facile, one-pot polyol method with acetic acid as the structure-director. Micrometre-sized 2D films and honeycomb-like spheres can be obtained using the uniform 3D bismuth telluride nanocrystals as building blocks.

Q. Yuan, K. Rader, M. M. Hussain

DOI: 10.1039/C1CC14556H (Communication) Chem. Commun., 2011, 47, 12131-12133