Chinese scientists have created the world’s first rubber band that converts body heat into electricity, potentially paving the way for smartwatches and other wearable devices that will charge automatically, according to South China Morning Post.The research team said the material combined elasticity with efficient thermoelectric conversion.
“Until now, all reported high-performance thermoelectric materials have realised only flexibility, rather than elasticity,” they wrote in a paper published in the peer-reviewed journal Nature last month.
Wearable devices currently need bulky batteries or frequent charging but the research raises the prospect of a ready and constant power supply that removes the need for charging.
This is achieved based on thermoelectric laws, whereby temperature differences can generate power – in the same way that the Watt steam engine converted the heat of boiling water into energy, paving the way for the first locomotives.
Since the human body temperature is usually around 37 degrees Celsius (98.6 Fahrenheit) and ambient temperatures typically range from 20 to 30 degrees, the Chinese team tried to harness the temperature difference and convert it into electrical energy.
Thermoelectric materials have been in use for years. For example, deep space probes rely on a radioactive isotope thermoelectric generator to power them when solar energy is unavailable.
We are the first in the world to propose the concept of thermoelectric rubber, said Lei Ting, materials scientist, Peking University.
But these are either inorganic materials that are “hard like stones” or organic materials that, although softer, perform poorly when stretched, according to Lei Ting, a materials scientist at Peking University’s School of Materials Science and Engineering and the corresponding author of the study.
“We are the first in the world to propose the concept of thermoelectric rubber,” he added.
Lei said that his team had been working to create a material that could bend, stretch and cling to the skin. “Such thermal devices are comfortable to wear and efficiently convert the body’s heat energy into electrical energy with less heat loss,” he said.
He added that, in theory, if the material did not break down or suffer additional damage, it would continue to supply power indefinitely.
The key innovation lies in the hybrid structure that blends and cross-links semiconducting polymers with elastic rubber. By engineering a nanofibre network within the material, the researchers said they had achieved an unprecedented level of stretchability while maintaining high electrical conductivity.
After this treatment, the material stretched to more than 850 per cent of its original length, the paper said. After being stretched to 150 per cent, it was able to recover more than 90 per cent of its original shape, a level comparable with natural rubber.
Special dopants, or doping agents – a small amount of a substance added to a material to alter its physical properties – further boosted performance, resulting in room-temperature thermoelectric properties that rival conventional inorganic materials of this type.
“This isn’t just about charging wearables,” Lei said, pointing to a much wider range of potential applications.
For example, it could be possible to power communications equipment in remote and isolated areas simply by lighting a fire.
The group is also planning to incorporate the material into clothing, which could both charge a mobile phone in the pocket and regulate body temperature by using its semiconductor wires to transfer body heat to the exterior of the clothing.
The innovation could also have applications in the medical field. For example, cardiovascular examinations currently require patients to wear an electronic device for a week to collect sufficient data.
This needs a relatively large battery and circuitry components, but the new material could allow medical sensors to be worn close to the body without the need for additional batteries.