Breakthrough paves the way for devices powered by body heat

Forget hunting for a power socket; the heat from your wrist might soon be enough to keep your smartwatch running indefinitely. Once a concept confined to science fiction, the idea of "body-heat powered" electronics is moving closer to reality.

A team of Chinese scientists has developed a groundbreaking plastic film capable of converting body heat — or even the warmth from a car engine — into electricity with record-breaking performance.

The study, published on Friday in the journal Science, addresses a major hurdle for next-generation wearable technology: finding a sustainable way to power the devices worn every day. As the use of smartwatches, fitness trackers, and medical patches becomes more widespread, the need for daily charging is a growing inconvenience. To solve this, researchers are looking at thermoelectric materials, which can turn temperature differences into power.

These materials function through the Seebeck effect. Essentially, when one side of a material is hotter than the other, electrons naturally flow toward the cooler side. This movement of electrons creates an electric current.

Historically, the best materials for this were usually rigid, heavy, and often toxic. While flexible plastics (polymers) are lighter and easier to wear, they are usually not very efficient. The problem is a molecular-level contradiction: to work well, a material needs to block heat from moving across it (low thermal conductivity) while allowing electricity to flow through it easily (high electrical conductivity). Usually, if a material is good at one, it's good at both — which ruins the energy conversion.

Liu Liyao, an associate professor at the Chinese Academy of Sciences' Institute of Chemistry, said the team overcame this by creating a "hierarchical porous structure".

Think of it as a plastic sponge filled with holes of all different sizes, ranging from nanometers to micrometers. This chaotic, hole-filled structure acts like a rugged mountain range for heat, making it difficult for heat waves to pass through. Meanwhile, the narrow "bridges" between these holes force the polymer molecules to line up in neat, orderly rows.

These rows act like high-speed highways for electrons, allowing electricity to zip through with minimal resistance. This dual-action design reduced heat leakage by 72 percent while increasing electrical flow by 52 percent.

The new film also set a record for flexible materials. It achieved a "thermoelectric figure-of-merit" — a score used to measure how efficiently a material converts heat to power — of 1.64 at about 70 C. This shatters the previous record of 1.4 for similar flexible materials.

In a laboratory test, a piece of the film measuring 10 centimeters by 8 cm was attached to a person's body and successfully generated 9 millivolts of electricity.

While that is a small amount, the researchers estimate that scaling the material up to larger surfaces could power wireless sensors and other ultra-low-power electronics.

Because the material is a type of plastic, it is compatible with industrial printing techniques. This means it could eventually be "printed" in large rolls, similar to how newspapers are produced.

Liu said that with further work to lower costs and stabilize performance, the "power-generating plastic" could be used for everything from medical sensors to green energy systems on Earth and even power generation in space.

limenghan@chinadaily.com.cn