Atomic force microscopy has revealed that structural water in tungsten oxide results in smaller deformation rates from ion intercalation. Image: Veronica Augustyn, NC State University.Researchers already knew that a novel material with atomically thin layers of water held promise for energy storage applications, but they have now discovered that the water is performing a different role than anyone anticipated. This finding was made possible by a new atomic force microscopy (AFM) method that measures the sub-nanoscale deformation rate in a material in response to changes caused by energy storage.
The researchers studied crystalline tungsten oxide dihydrate, which consists of crystalline tungsten oxide layers separated by atomically thin layers of water. This material is of interest because it holds promise for helping to store and release energy quickly and efficiently. Up to now, however, it has not been clear what role the water plays in this process.
To address this question, researchers from North Carolina (NC) State University, the Oak Ridge National Laboratory and Texas A&M University employed a new AFM method. This relies on using AFM to track the expansion and contraction of the material at the atomic scale and in real time as an electronic instrument called a potentiostat moves charge in and out of the material. This technique allowed the team to detect even minor deformations in the material as charge moved through it.
"We tested both crystalline tungsten oxide dihydrate and crystalline tungsten oxide, which lacks the water layers," says Veronica Augustyn, an assistant professor of materials science and engineering at NC State and corresponding author of a paper on this work in ACS Nano. "And we found that the water layers appear to play a significant role in how the material responds mechanically to energy storage."
"Specifically, we found that the water layers do two things," explains Ruocun ‘John’ Wang, a PhD student in Augustyn's lab and lead author of the paper. "One, the water layers minimize deformation, meaning that the material expands and contracts less as ions move in and out of the material when there are water layers. Two, the water layers make the deformation more reversible, meaning that the material returns to its original dimensions more easily."
"In practical terms, this means that the material with water layers is more efficient at storing charge, losing less energy," Augustyn says.
This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.