Wiring a Rose to Store Energy

Roses are a common sign of love, or of an attentive gardener, not a common sign of cutting-edge scientific research. However, new work published in the Proceedings of the National Academy of Sciences shows roses in a whole new light—as beautiful energy storage devices. This work brings us one step closer to being able to harvest energy from plants.

Plants are clearly an important part of our ecosystem, and are essential to our survival. We rely on them for food, clothing, oxygen, heat, rain, and numerous other things. They put the seasons on display and bring warmth and color into our lives. In addition, say the Linköping University researchers who performed this new research, plants are an untapped resource when it comes to producing advanced materials, electronics, and energy technology.

If you fill a vase with colored water and place a freshly cut white flower in the vase, after a day or two the flower will take on the color of the water. This is because the stem absorbs the dye along with the water. The dye is then transported through the plant via the channels that distribute water and nutrients, eventually reaching the petals of the flower.

The Linköping University researchers have taken this activity to a whole new level. In 2015, they dissolved a special polymer in water and immersed a rose cutting in the solution. Like the dye, the mixture was absorbed and carried through the plant, although the polymer wasn’t able to reach the leaves and petals. Inside the plant, the polymer turned into a kind of electrically conducting gel that stretched along the transportation channels. In other words, it became a wire inside of the plant. The researchers went so far as to demonstrate that the rose stem could become a fully functional transistor.

Since then, the team has developed a new polymer solution. After immersing a rose cutting in the new solution for 24 hours, the researchers rinsed the rose and peeled off the outer layer of the stem to reveal dark, continuous lines. These lines—thin, conducting chains formed by the molecules in the solution—ran through the stem and into the leaves and petals forming long, thin electrical wires.

The researchers ran several tests to measure the properties of the wires and explore their structure and development. These wires are even more conducting than the ones produced with the previous method. The biggest advantage to this method, however, is that the solution can pass into the leaves and petals. This means that the entire structure of a plant can be considered in the design of electronic devices and circuits, not just the stem.

As a next step in exploring the possibilities of plant-based electronic devices, the researchers successfully stored electrical energy in the rose. Using two parallel wires in the plant and a couple of metal probes, they were able to create a supercapacitor—an electrical component that stores energy so that it can be released when needed. The anatomy of a plant is actually very conducive to this, and the researchers were able to charge and discharge the supercapacitor hundreds of times without significant performance loss.

Although electronic plant technology is still young, these experiments have generated a lot of interest in what might someday be possible. Will we be able to design systems inside living plants that can optimize their growth and function, providing an alternative to genetic engineering? Will we be able to harvest energy from photosynthesis in a cost-efficient, environmentally-friendly manner? Time will tell, but this research has certainly moved us further down that rose-lined path. As Sherlock Holmes said in Arthur Conan Doyle’s The Naval Treaty, “we have much to hope from the flowers.”

—Kendra Redmond