Grotthuss mechanism could revolutionise energy storage for high-power applications, study suggests

Proton-hopping is a promising basis for ultrafast charging/discharging - but more work needed

The Grotthuss mechanism, which was first discovered about 200 years ago, could revolutionise energy storage for high-power applications like electric vehicles or electricity grids, according to a new study led by the Oregon State University (OSU) researchers.

The study - which involved researchers from OSU's College of Science, Oak Ridge National Laboratory, the University of California Riverside, and the Argonne National Laboratory - demonstrated for the first time that diffusion may not be necessary for transportation of 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 study paper.

In the current study, the researchers built on work by Theodor von Grotthuss, a German-Lithuanian chemist who in early 19^th century discovered the process of proton hopping in water.

In the Grotthuss mechanism, an 'excess' proton (H+ ion) (or proton defect) in water quickly binds to an intact water molecule to form a hydronium ion (H3O+). Because water molecules are loosely joined together with hydrogen bonds, protons can 'hop' quickly from one to another. The result is the rapid diffusion of H+ ions in water. The mechanism is also observed in other hydrogen-bonded liquids.

"That's the beauty of it," said Xiulei (David) Ji, associate professor of chemistry, and the lead researchers of the study.

"If this mechanism is installed in battery electrodes, the proton doesn't have to squeeze through narrow orifices in crystal structures. If we design materials with the purpose of facilitating this kind of conduction, this conduit is so ready—we have this magic proton highway built in as part of the lattice."

The research team was able to demonstrate promising results using a hydrated electrode of Turnbull's blue dye.

However, they caution it will take more time to attain ultrafast charging and discharging in batteries that are practical for high-power applications like vehicles or grid energy storage.

The researchers say they have theoretically demonstrated sub-second charging and discharging of battery chemistry, but it will be a long journey to make electrodes suitable for consumer devices.

"Right now the battery community focuses on lithium, sodium, and other metal ions, but protons are probably the most intriguing charge carriers with vast unknown potentials to realise," said Ji.

The findings of the study are published in journal Nature Energy.