Linköping University researchers managed to make bean plants' roots electrically conductive. (Image Credit: Thor Balkhed/ Linköping University)
Linköping University researchers demonstrated that bean plants' roots become conductive and store energy when fed with a conjugated oligomers solution. This isn't the first time that plants can provide electrical capabilities, however. In 2015, Dr. Elena Stevrinidou revealed that circuits could form in a rose's vascular tissue. In that case, the plant's vascular system absorbed PEDOT, a conducting polymer, and formed electrical conductors that were utilized to produce transistors. In 2017, she showed that a conjugated oligomer, ETE-S, polymerized the plant, producing energy-storage conductors.
"We have previously worked with plant cuttings, which were able to take up and organize conducting polymers or oligomers. However, the plant cuttings can survive for only a few days, and the plant is not growing anymore. In this new study, we use intact plants, a common bean plant grown from seed, and we show that the plants become electrically conducting when they are watered with a solution that contains oligomers," says Eleni Stavrinidou.
For this study, the team used an ETE-S trimer, which becomes polymerized through the bean plants' natural process. In turn, a polymer conducting film forms on the plants' roots, causing the root system to operate as a network of conductors. With a conductivity of 10.8/cm, the roots stay conductive for at least four weeks. The team looked into whether the roots could have energy-storage capabilities. They developed a root-based supercapacitor that allowed the roots to function like electrodes during the charging and discharging process.
"Supercapacitors based on conducting polymers and cellulose are an eco-friendly alternative for energy storage that is both cheap and scalable," says Stavrinidou.
The electronic root system can store up to 100 times more energy than other plants in previous experiments. (Image Credit: Thor Balkhed/ Linköping University)
The root-based supercapacitor stored up to 100 times more energy than initial studies. Even more, the device could be used for longer periods due to the bean plants' longevity and growth. "The plant develops a more complex root system but is otherwise not affected: it continues to grow and produce beans," Stavrinidou says.
The results could lead to further sustainable energy storage developments and new biohybrid systems, such as functional materials and composites. Also, the electronic roots could progress toward developing communication between electrons and biological systems.
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