Researchers at Oregon State University have found that a chemical mechanism first described more than two centuries ago holds the potential to revolutionize energy storage for high-power applications like vehicles or electrical grids.
The research team led by Xiulei (David) Ji, associate professor in the Department of Chemistry, along with collaborators at the Argonne National Laboratory, the University of California Riverside, and the Oak Ridge National Laboratory, are the first to demonstrate that diffusion may not be necessary to transport ionic charges inside a hydrated solid-state structure of a battery electrode.
“This discovery potentially will shift the whole paradigm of high-power electrochemical energy storage with new design principles for electrodes,” said Xianyong Wu, a postdoctoral scholar at OSU and the first author of the article.
Findings were published today in Nature Energy.
“Coming up with Faradaic electrodes that afford battery’s energy density and capacitor’s power with excellent cycle life has been a big challenge,” said Ji, associate professor of chemistry. “So far, most of the attention has been devoted to metal ions – starting with lithium and looking down the periodic table.”
Grotthuss mechanism
The collaborative team, however, looked up – to the single proton of hydrogen – and they also looked back in time, to Theodor von Grotthuss, a German-born Lithuanian chemist who in 1806 penned the theory on charge transport in electrolytes.
Von Grotthuss was just 20, and living in a region beset with political upheaval, when he published “Memoir on the decomposition of water and of the bodies that it holds in solution by means of galvanic electricity” in a French scientific journal.
“In the turmoil of his time and place, he managed to make this big discovery,” Ji said. “He was the earliest to figure out how electrolyte works, and he described what’s now known as the Grotthuss mechanism: proton transferred by cooperative cleavage and formation of hydrogen bonds and O-H covalent bonds within the hydrogen-bonding network of water molecules.”
Here’s how it works: Electrical charge is conducted when a hydrogen atom bridging two water molecules “switches its allegiance” from one molecule to the other, Wu explains.
“The switch kicks disjointed one of the hydrogen atoms that was covalently bonded in the second molecule, triggering a chain of similar displacements throughout the hydrogen-bonding network,” he said. “The motion is like a Newton’s cradle: Correlated local displacements lead to the long-range transport of protons, which is very different from metal-ion conduction in liquid electrolytes, where solvated ions diffuse long distances individually in the vehicular manner.”
Added Ji: “The cooperative vibrations of hydrogen bonding and hydrogen-oxygen covalent bonds virtually hand off a proton from one end of a chain of water molecules to the other end with no mass transfer inside the water chain.”
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