What to do with fallen leaves? Other than decompose and give nutrition to the soil, they could also be used to store energy, becoming the raw material of batteries.
Since long time scientists were looking for alternative materials for the production of batteries, able to be easily accessible but above all sustainable. A team of researchers at the University of Maryland has found a new solution in fallen leaves, abundant raw material at no cost.
"Leaves are so abundant. All we had to do was pick one up off the ground here on campus" said Hongbian Li, professor in the Department of Materials Science and Engineering at UMD. Previous studies had shown that the skin of fruit such as melon and banana could be used as raw material to produce batteries, but leaves certainly require less processing and preparation.
On this basis, scientists in Maryland have considered using leaves and sodium instead of lithium, commonly used. Why sodium? In their opinion, sodium is able to hold a charge, although it can not handle many charge and discharge cycles as lithium does. One of the most challenging obstacles was to find a material for the anode that was compatible with the sodium. Graphene has been tested but times and production costs are very high. At that point, researchers simply tried to heat a maple leaf for one hour at 1,000 ºC to burn the carbon structure underneath.
The bottom side of the maple leaf is rich in pores for absorbing water. "The natural shape of a leaf already matches a battery’s needs: a low surface area, which decreases defects; a lot of small structures packed closely together, which maximizes space; and internal structures of the right size and shape to be used with sodium electrolyte" said Fei Shen, a visiting student in the Department of Materials Science and Engineering author of the study.
According to scientists, leaves have been designed by nature to store energy for later use, and using leaves in this way could allow humans to create batteries with a low environmental impact.
The next step now will be to study different types of leaves to find those characterized by a certain thickness, structure and flexibility to achieve the best electrical energy storage. The solution, once again, resides in the hands of Mother Nature.