"We are the first to show that 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."Tian Li, University of Maryland
A University of Maryland (UMD)-led team of researchers has created a wood-based heat-to-electricity device that runs on ions and could someday harness the body's heat to provide energy.
Led by UMD researchers Liangbing Hu, Robert Briber and Tian Li of the Department of Materials Science, and Siddhartha Das of the Department of Mechanical Engineering, the team transformed a piece of wood into a flexible membrane that generates energy from ions. This energy is generated by the charged channel walls and other unique properties of wood's natural nanostructures. With this new wood-based technology, the researchers can use a small temperature differential to efficiently generate ionic voltage, as demonstrated in a paper published in Nature Materials.
If you've ever been outside during a lightning storm, you've seen that generating charge between two very different temperatures is easy. But for small temperature differences, it is more difficult. The researchers now claim to have successfully tackled this challenge. According to Hu, they have "demonstrated their proof-of-concept device, to harvest low-grade heat using nanoionic behavior of processed wood nanostructures".
Trees grow wood with channels that move water between the roots and the leaves. These channels cover a wide range of sizes; at the level of a single cell, they are just nanometers or less across. The team has harnessed these channels to regulate ions.
The researchers used basswood, which is a fast-growing tree with low environmental impact. They treated the wood and removed two components – lignin, which makes the wood brown and adds strength, and hemicellulose, which winds around the layers of cells binding them together. This just left the cellulose, which gives wood its signature flexibility. The treatment process also converted the structure of the cellulose from type I to type II, which is key to enhancing ion conductivity.
The researchers sandwiched a membrane made of a thin slice of this treated wood between platinum electrodes and then soaked it with a sodium-based electrolyte to regulate the ion flow inside the tiny channels and generate an electrical signal. "The charged channel walls can establish an electrical field that appears on the nanofibers and thus help effectively regulate ion movement under a thermal gradient," said Tian Li, first author of the paper.
Li – who was named as one of Forbes ‘30 Under 30’ in Energy in 2018 – explained that the sodium ions in the electrolyte make their way into the aligned channels. This is made possible by the crystal structure conversion of the cellulose and by dissociation of the surface functional groups.
"We are the first to show that 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," Li said.
This story is adapted from material from the University of Maryland, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.