Imagine it: you’ve gone out to the park for a run, you’ve been giving it your all for forty minutes, you’re about to finally complete your second kilometer and you stop, hot as a penguin in a sauna, to make a call on your mobile. But it has run out of battery. No problem! Because you can connect the phone to your paper bracelet, which converts the heat that your body gives off into electricity.
This scene, which, for now, is still science fiction – although there are already promising thermoelectric materials capable of transforming residual heat into small voltages – is a little closer to becoming a reality thanks to the work of a team of researchers from the Institute of Science of Materials of Barcelona (ICMAB-CSIC), who have created a new material: a thermoelectric paper.
“This device is composed of cellulose produced in the laboratory by bacteria, with small amounts of a conductive nanomaterial –carbon nanotubes– , so its production is sustainable and respectful of the environment,” says Mariano Campoy-Quiles, one of the authors of the research, published in the journal Energy & Environmental Science .
“In the near future, it could be used as a wearable device, in medical or sports applications, for example,” adds the researcher. And if the efficiency of the device were further optimized, this material could lead to intelligent thermal insulation . “
Another of the researchers, Anna Roig, explains that, “due to the high flexibility of cellulose and the scalability of the process, these devices could be used in applications where the residual heat source had irregular shapes or covered large areas , since they could completely cover with the material ”.
It is not manufactured, it is cultivated
In the production of this thermoelectric paper, no toxic elements are used and cellulose can be easily recycled, degrading it through an enzymatic process that converts it into glucose and that allows the carbon nanotubes, which are the most expensive element of the device, to be recover. “The intention is to get closer to the concept of circular economy – points out Roig -, using sustainable materials that are not toxic to the environment, that are used in small quantities and that can be recycled and reused.
“Instead of making a material for energy, we grow it,” says Campoy-Quiles. Bacteria, dispersed in an aqueous culture medium containing sugars and carbon nanotubes, produce nanocellulose fibers that end up forming the device, where the nanotubes are perfectly dispersed ”.
“Thanks to their nanometric diameter and a few microns long,” continues the scientist, “carbon nanotubes allow, with very little quantity, to achieve electrical percolation, that is, a continuous path where electrical charges can travel through the material, allowing cellulose to be conductive and, at the same time, thermal insulator ”.
Image: Thermoelectric paper produced by bacteria in the laboratory (ICMAB).
