Flexible, non-toxic energy converters could power portable devices – sciencedaily

A wide variety of portable and portable electronic devices have become a large part of our daily lives, so a group of researchers at Stanford University wondered if these could be powered by harvesting electricity from of the waste heat that exists all around us.

Another inspiration came from a desire to ultimately fabricate energy conversion devices from the same materials as the active devices themselves, so that they can blend together as an integral part of the total system. . Today, many power supplies for nanomedical devices come from several types of batteries which must be separated from the active part of the systems, which is not ideal.

In Letters of Applied Physics, AIP Publishing, the researchers report the design and manufacture of single-wall carbon nanotube thermoelectric devices on flexible polyimide substrates as the basis for portable energy converters.

“Carbon nanotubes are one-dimensional materials, known for their good thermoelectric properties, which means developing a voltage between them in a temperature gradient,” said Eric Pop, professor of electrical engineering and materials science. “The challenge is that carbon nanotubes also have high thermal conductivity, which means it’s difficult to maintain a thermal gradient across them, and they have been difficult to assemble into low-cost thermoelectric generators.”

The group uses arrays of printed carbon nanotubes to meet these two challenges.

“For example, carbon nanotube spaghetti arrays have much lower thermal conductivity than carbon nanotubes taken alone, due to the presence of junctions in the arrays, which block heat flow,” Pop said. “In addition, direct printing of such arrays of carbon nanotubes can dramatically reduce their cost when scaled up.”

Thermoelectric devices generate electrical energy locally “by reusing waste heat from personal devices, appliances, vehicles, business and industrial processes, computer servers, time-varying solar lighting and even the body. human, “said Hye Ryoung Lee, senior author and research scientist.

“To remove the barriers to the large-scale application of thermoelectric materials – toxicity, scarcity of materials, mechanical brittleness – carbon nanotubes offer an excellent alternative to other commonly used materials,” said Lee.

The group’s approach shows a path towards the use of carbon nanotubes with printable electrodes on flexible polymer substrates in a process believed to be economical for high volume manufacturing. It is also “greener” than other processes because water is used as a solvent and additional dopants are avoided.

Flexible and portable energy collectors can be incorporated into fabrics or clothing or placed on unusual shapes and form factors.

“In contrast, traditional thermoelectrics that rely on bismuth telluride are brittle and rigid, with limited applications,” Pop said. “Carbon-based thermoelectrics are also more environmentally friendly than those made from rare or toxic materials like bismuth and tellurium.”

The most important concept in the group’s work is to ‘recycle energy as much as possible, converting the uneven heat distribution into electrical energy for use for the next cycle of operation, which we have demonstrated using one generation non-toxic nanotube-based thermoelectric, ”said Yoshio Nishi, professor of electrical engineering. “This concept is in perfect harmony with the global goal of reducing our total energy consumption.”

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