In a First, Scientists See How Water Stores Extra Protons

In a First, Scientists See How Water Stores Extra Protons

To make efficient hydrogen energy technology a reality, from generating hydrocarbons through electrolysis up to next-generation chemical fuel cell technology, scientists need to understand how hydrogen atoms move through water.

A neutral molecule of water contains two hydrogen atoms that are bonded to one oxygen atom. The entire structure bends to give the molecule a partially-positive and partially-negative side, much like a magnet. Zooming in on a glass water would reveal trillions of these molecules, as well as some individual hydrogen atoms that have lost electrons (or just protons). For 200 years researchers have theorized that these protons hop from one water molecule to another by attaching to the nearest molecule and kicking off one of the protons already bonded there. The proton then bonds to the next neighbor. A team of scientists from Beijing has now taken images of such particles under a microscope, helping to illuminate how these jumps happen.

Models predicted this process would occur in two ways. One, a proton bonds directly with a single water molecular, turning it into a positive Ion. The proton is stabilized by three surrounding neutral water molecules. The other option is to place the extra proton between two neutral water molecules’ negative ends so that each takes on the burden of the positive charge.

Researchers were capable of verifying these orientations using atomic-force microscopescopy, a technique that generates images through the tracing of the nanoscopic points of a specialized needle across bumps on a surface. Jing Guo, a Beijing Normal University chemist, and her colleagues used this instrumentation to image a molecule-deep network made of water and a slip of steel. They also revealed how additional protons affected that network. Their work was published in Science.

It was necessary to take extremely sensitive measurements to distinguish between the two water configurations. “The position of protons along the hydrogen bond differed only by about 20 picometers,” Guo says–less than half the length of a hydrogen atom itself. After long struggles , we are excited to find the underlying images.

The team discovered that these two configurations occur at different frequencies and ratios depending upon the metal to which the water was frozen. They also used electricity to make water flip-flop between the two configurations. “It’s amazing that they can [directly] see these things,” Thomas Kuhn, a theoretical chemicalist at Paderborn University in Germany who was not involved with this work, said. He says, “It opens up the door to study [hydrogen generation] mechanisms.” “And maybe out of that, good stuff comes.”

This article was originally published with the title “Water Network” in Scientific American 327, 5, 26 (November 2022)

doi: 10. 1038/scientificamerican1122-26a

ABOUT THE AUTHOR(S)

    Lars Fischer is a chemist and works as a journalist and editor at Spektrum der Wissenschaft.

      Fionna M. D. Samuels was a 2022 AAAS Mass Media Fellow at Scientific American. She is currently pursuing a Ph.D. degree in chemistry at Colorado State University. Follow her on Twitter @Fairy__Hedgehog

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