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‘Flat water’ provides a battery boost

Atomically thin liquid layers could help 2-D materials improve energy-storage devices

by Matt Davenport
May 15, 2017 | A version of this story appeared in Volume 95, Issue 20

An electron micrograph shows alternating layers of water and tungsten oxide in an electrode material. The crystal structure of tungsten oxide spaced by single layers of water is shown in an attached illustration.
Credit: Chem. Mater.
Alternating layers of water sheets and tungsten oxide crystals—shown in purple in the illustration—appear as stripes in the electron micrograph of electrode material shown on the right.

A popular approach for developing better batteries and other energy-storage devices is incorporating atoms-thick sheets of solid-state materials. This strategy may hold for liquids, too. Researchers have found that test devices using tungsten oxide electrodes have improved energy-storage kinetics when thin layers of water are confined between crystalline WO3 sheets (Chem. Mater. 2017, DOI: 10.1021/acs.chemmater.6b05485). Hydrated electrodes charge and discharge faster than their anhydrous counterparts, reports a team led by Veronica Augustyn of North Carolina State University. Further, the hydrated ­material better maintains its charge capacity and energy efficiency at these faster time­scales. The intercalated water layers likely lower the energetic barrier encountered by ions moving from liquid electrolytes to solid electrodes, although the team is investigating this hypothesis. Tungsten oxide provides a good model system for these types of fundamental studies, though the material is too heavy for commercial applications, Augustyn says. Still, she’s not alone in thinking this work can help further develop other, more attractive materials, including two-dimensional carbides and nitrides known as MXenes (pronounced max-enes). “I’m confident this concept can be applied to many other 2-D and layered materials, helping us to develop high-power and high-energy-storage devices,” comments MXene pioneer and innovator Yury Gogotsi of Drexel University.


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