The idea of using wood to generate energy is usually associated with directly combusting wood to produce heat. But a University of Maryland-led team of researchers has created a heat-to-electricity device that runs on ions and which could someday harness the body’s heat to provide energy.
A team comprising Liangbing Hu, Robert Briber and Tian Li, all of the University of Maryland’s department of materials science, and Siddhartha Das of the department of mechanical engineering, transformed a piece of wood into a flexible membrane that generates energy from the same type of electric current (ions) that the human body runs on. This energy is generated using charged channel walls and other unique properties of the wood’s natural nanostructures. The wood-based technology relies on using a small temperature differential to efficiently generate ionic voltage, as demonstrated in a paper published March 25 in the journal Nature Materials.
Generating a charge for a small temperature differential is considered more challenging than for a wide temperature differential. But the research team says they have successfully tackled this challenge using the nanoionic behavior of processed wood nanostructures to harvest low-grade heat.
The researchers used basswood, which is a fast-growing tree with low environmental impact. They treated the wood and removed two components—lignin, that 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. It regulates the ion flow inside the tiny channels and generates 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,” saysTian Li, first author of the paper. .
“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,” says Li.