We’re not far off from plugging in our plants. The boundary between organic, leafy greens and metallic electronics is becoming increasingly blurred, although the end result won’t exactly look like a LED grass or an electrified salad (sadly). Still, there’s an impressive range in where plants and electronics are overlapping, starting with some well-roasted leaves that are may soon be recycled into capacitors.
Using leaves to manipulate a current
Appropriate to their names, Chinese phoenix trees are being reborn in fire as highly conductive carbon microspheres. Thankfully, the whole tree doesn’t need to be destroyed in this process, as the carbon is obtained from dead leaves that pile up in autumn. That convenience aside, you probably aren’t going to start getting capacitors out of your yard waste any time soon, as these leaves are dried, powered, heated for 12 hours at 428° Fahrenheit, mixed with potassium hydroxide, then heated again in rapidly changing temperatures up to 1,472°.
It’s a lot of work, but the payoff is a renewable source of highly porous carbon spheres that may pave the way for a variety of plant-based electronic components. The pores create a very high surface area for the tiny pellets, which may even qualify as supercapacitors transferring three times more power than graphene supercapacitors. The phoenix tree leaves work especially well, but researchers are already looking into other plants like potato skins, corn straw, pine wood and rice straw as other sources of conductive carbon.
Measuring the current in leaves
On the flip-side, if you’re looking to produce more foliage instead of electricity, there’s still a reason to wire up a plant’s leaves. Lightweight electrical sensors are being clipped onto leafy crops to measure how well they conduct electricity in differing soil conditions. Once baselines are established, these tiny variances may help measure exactly when a plant is dried out enough to need a drink, reducing a farm’s water usage.
To make these measurements, a small sensor was clipped to leave on different plants for 11 days. As the plants absorbed more or less water, their leaves would swell or shrink at the same time. That tiny change in thickness would then alter the flow of electricity through the leaf enough to be detected, and could then inform a farmer, or automated irrigation system, when plants were really ready for more water, even if the normal watering schedule didn’t sync up. These measurements were compared against a separate sensor in the soil to verify that they were on the right track. The measurements are complicated by the fact that photosynthesis can also change the flow of electricity through a leaf, but researchers are still confident this system will allow farms to be much more sensitive to their stressed plants.
Source: High-Tech Electronics Made From Autumn Leaves, Scienmag