Tomato skin and graphene to generate electricity with body heat | Technology

In mid-1945, when World War II advanced towards its end, Russian Red Army troops used a chimney to communicate by radio. It was relatively straightforward using two lead plates joined by copper wires. They left one outdoors and the other in the fire. The temperature difference generated an electron flow, that is, electric current. It is known as the Seebeck effect, which is now used by researchers in Malaga so that any textile garment can produce small amounts of energy, as they have shown in a work published in the magazine Advanced Functional Materials. Of course, they do it with biodegradable, sustainable and much lighter materials: tomato skin and graphene nanoparticles, which spread on cotton fabrics like a shirt. When dressing it, the contrast between body heat and room temperature does the rest.

In a small laboratory of the Faculty of Sciences of the University of Malaga, Susana Guzmán and Alejandro Heredia show a glass jar where they keep what they look like breakfast cereals. They are not. These are small pieces of cutin, the skin of tomato. An efficient vegetable polymer as a container - in nature it protects the fruit from rain, heat, bacteria or water losses - that they break down into monomers (small molecules). These are introduced into a solution of water and ethanol along with the carbon nanoparticles that make up graphene. When applying heat, the mixture can be expanded on any fabric - they have chosen cotton because it is biodegradable - by means of a spray. The biotint impregnates graphene with textile fibers, which clings to them thanks to tomato skin, which acts as a glue. The heat also causes the curtain to polymerize again until it becomes solid. The end result is a black substance that covers the garment and can generate electricity. When the researchers put some led lights on it, they turn on.

"We have achieved a flexible, lightweight, sustainable and relatively inexpensive material that generates electricity," says Manuel Heredia, researcher Ramón y Cajal of the Department of Plant Improvement and Biotechnology of the Institute of Subtropical and Mediterranean Horticulture (IHSM), mixed center of the Higher Center of Scientific Research (CSIC) and the University of Malaga (UMA). The first application has been a shirt that, impregnated in this solution, generates electricity thanks to the difference between the 36 degrees of body temperature and the outside. The power is still very small. "The important thing is that the step is taken: now it's time to do better, optimize it and increase the amount of energy generated," adds Heredia. What least worries him is obtaining tomato skin. In Spain about 60,000 tons are discarded a year and the industry is delighted to give it away to science because eliminating it is expensive. "And it is a much more sustainable and cheaper substance than tellurium, lead or germanium, materials commonly used to make thermoelectric devices," says the scientist.

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A detail of the investigation.

enlarge photo

A detail of the investigation.

Heredia works with Susana Guzmán, a postdoctoral researcher in the Department of Molecular Biology and Biochemistry of the UMA, in developing new possibilities. As the option to make garments that serve mountaineers, military or who may be in extreme situations and without the possibility of finding a plug. They could also energize sensors dedicated to health - such as controlling heart rate - or measuring the levels of contamination around us and even that the shirt can recharge the mobile phone or other electronic devices.

“Reduce thermal conduction of materials [la capacidad de transmitir el calor] it will allow us to increase the power we can generate, ”says Pietro Cataldi, from the National Graphene Institute of the University of Manchester and co-author of the published work. The researcher believes that the next generation of biocomposites in which Malaga researchers already work will be superior because, among other things, it will improve their stability during tissue washes. That was the first problem: when Cataldi used polymers derived from petroleum to achieve the Seebeck effect, the materials disappeared after passing a few times through the washing machine. Now the biopolymer made from tomato skin works as an adhesive and graphene remains.

The project has been developed during the last year halfway between the University of Malaga and the Italian Materials Institute of Genoa, where Heredia and Guzmán have worked for seven years. Both returned last spring to the IHSM and the UMA. And Cataldi, who was then researching there, had asked them for collaboration to incorporate electronics into textile materials. They had already worked together to create a wifi antenna made with tomato skin - as a support - and graphene - as a driver - that worked. So when Cataldi asked for help again, they continued investigating with the cutin, which they break down with chemical procedures in monomers to then build a polymer in the laboratory with the size, shape and properties they need. It's like a Lego: they disassemble the pieces of the curtain and, with them, they rebuild another figure. "This is not sewing skins," said Manuel Heredia, director of the research group and Professor in Biochemistry, whose knowledge has also been a fundamental piece of research. He began to synthesize in the laboratory polymers with properties similar to tomato skin at the beginning of the 21st century. A work in which he works since then with Jesús Benítez, of the Institute of Material Sciences of Seville, in search of new applications.


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