Thermoelectric generators (TEGs) are devices that can convert temperature gradients into electricity. Such devices are extremely useful for generating electricity for remote sensors that cannot be connected to the mains power grid. A typical TEG consists of one side (top or bottom) that radiates heat for cooling and the other side that absorbs heat from the sun or the environment.

This creates an out-of-plane temperature gradient that is converted into electricity. However, such requirements often require cumbersome, complex and inefficient structures. This makes it difficult to integrate TEGs with other components or systems, limiting their application in renewable energy systems.

Fortunately, researchers in Korea may now have a way to overcome these challenges. In a new study, researchers led by Professor Yang Min-song from the Gwangju Institute of Science and Technology (GIST) report a new flexible, lightweight and biodegradable TEG that takes its inspiration from an unexpected place: zebra skin. Essentially, the design uses a pattern that resembles the black and white stripes of a zebra to create a high in-plane temperature gradient to generate electricity. Breakthrough released Science Advances.

“Traditional TEG designs are large and cumbersome because they rely on natural convection, which results in an out-of-plane temperature gradient. This requires rigid insulators, limiting the use of TEG in flexible and portable devices. We have now moved beyond this paradigm in our development to create a flexible biodegradable onboard device. This increases its applicability while reducing its environmental impact, making it scalable, integrated and sustainable,” explains Professor Song.

The researchers used poly(L-lactide-co-ε-caprolactone) (PLCL), a white, flexible and biodegradable material, to make TRH. PLCL reflects sunlight and emits infrared (IR) radiation, cooling the space underneath. The researchers coated this material with black-to-eye black poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) or (PEDOT:PSS), producing stripes similar to PLCL versus zebra skin stripes.

The reason PEDOT:PSS appears black is because it absorbs sunlight hitting it and reflects IR radiation from below (emitted by the PLCL). This, in turn, increases the temperature of the area under the black bars, creating alternating hot and cold areas, a temperature gradient that can then be converted into electricity.

The researchers achieved this transformation by using an array of silicon nanomembranes in their design. The new design was able to create a maximum temperature difference of 22°C and a maximum energy density of 6 µW/m². In addition, the device became fully biodegradable with no residual by-products in just 35 days.

With these outstanding features, the new TEG design is sure to open the door to scalable, environmentally friendly energy systems.

“The pandemic has led to the proliferation of disposable masks and protective equipment, which is having a huge impact on the environment. This highlights the need for sustainable and environmentally friendly solutions such as TEGs that can be incorporated into such portable devices to perform specific functions such as power generation. and emotions,” says Professor Song. “Our design can fill this gap due to its lightweight and biodegradable nature. It can also be easily integrated into a variety of energy and smart grid technologies, further enhancing their functionality and impact.”