Researchers have transformed a piece of wood into a flexible membrane that generates energy from the same type of electric current (ions) on which the human body runs. This energy is generated using charged channel walls and other unique properties of the wood’s natural nanostructures. With this new wood-based technology, a small temperature differential can be used to efficiently generate ionic voltage.
Trees grow channels that move water between the roots and the leaves. These are made up of fractally smaller channels — at the level of a single cell, channels just nanometers or less across. These channels were harnessed to regulate ions.
Basswood, a fast-growing tree with low environmental impact, was used. The wood was treated and two components removed: lignin, which makes the wood brown and adds strength, and hemicellulose, which winds around the layers of cells, binding them together. This gives the remaining cellulose its signature flexibility. This process also converts the structure of the cellulose from type I to type II, which is a key to enhancing ion conductivity.
A membrane made of a thin slice of wood was bordered by platinum electrodes, with sodium-based electrolyte infiltrated into the cellulose. They regulate the ion flow inside the tiny channels and generate electrical signal. The charged channel walls can establish an electrical field that appears on the nanofibers and helps effectively regulate ion movement under a thermal gradient. The sodium ions in the electrolyte insert into the aligned channels, which is made possible by the crystal structure conversion of cellulose and by dissociation of the surface functional groups.
This type of membrane, with its expansive arrays of aligned cellulose, can be used as a high-performance, ion-selective membrane by nanofluidics and molecular streaming and greatly extends the applications of sustainable cellulose into nanoionics.