Water conducts electricity – it’s a well-known fact and it’s what we were taught in primary school. But, the process by which individual molecules pass along the positive charge has kept us confounded for many years. Now, for the first time ever, a team of researchers from the University of Washington and Yale University have witnessed how water molecules pass along extra protons during the process of conductivity.

“This fundamental process in chemistry and biology has eluded a firm explanation,” said Anne McCoy, a professor of chemistry at the University of Washington. “And now we have the missing piece that gives us the bigger picture: how protons essentially ‘move’ through water.”

The process by which water conducts electricity is known as the Grotthuss mechanism. First proposed by Theodor Grotthuss in 1806, and is a process by which excess protons (after being introduced in water) pass quickly through the fluid, riding a transient, ever-shifting network of loose bonds connecting water molecules.

But, the passage of excess protons and the way they are relayed to neighboring molecules happens almost instantly that, in the study, it rendered the process useless in capturing the vibrations of water molecule using traditional spectroscopy.

Illustration of the Grotthuss mechanism - The process by which water conducts electricity.
Illustration of the Grotthuss mechanism: Water molecules pass along an extra proton. Oxygen atoms are in red, with hydrogen atoms in grey. [Credit: Matt K. Petersen]
“With spectroscopy, you hit objects with a beam of photons, see how those photons are scattered and use that scattering information to determine information about the object’s structure and arrangement of atoms,” explained McCoy. “And this is where Mark Johnson’s lab at Yale has really been a leader — in adapting spectroscopy to better capture this transfer of protons among water molecules.”

Mark Johnson, lead author of the study, made some progress by figuring out how to fast-freeze the proton relay to slow the chemical process. This gave the researchers enough time to visualize the Grotthuss mechanism using spectroscopy.

But again, these “spectroscopic snapshots” which used infrared scanning, were still too blurry due to vibrations in chemical bonds. So the team switched to heavy water – water made by replacing hydrogen atoms by a heavier isotope called deuterium, and decided to observe the proton exchange within it. And when the team chilled the molecules to almost absolute zero, they were able to see the transfer of protons.

“In essence, we uncovered a kind of Rosetta Stone that reveals the structural information encoded in color,” explained Johnson. “We were able to reveal a sequence of concerted deformations, like the frames of a movie.”

The team believes with this new insights into how water conducts electricity, it could lead to better understanding of chemical processes that occur at the surface of water, and help explain active debate among scientists regarding whether the surface of water is more or less acidic than the bulk of water.

The findings may not have immediate purpose for now, but in the near future, it could lead to the development of alternative energy technologies and pharmaceuticals.