New understanding of ionic interactions with graphene and water can improve water purification processes and electrical energy storage

A research team led by Northwestern engineers and researchers at the Argonne National Laboratory has found new discoveries in the role of ionic interaction. graphene and water. The approaches can provide batteries with the design of new high-energy-efficient electrodes or provide backbone ionic materials for neuromorphic computer applications.

They are known for their exceptional properties, from mechanical resistance to electronic conductivity and wet transparency. Graphene plays an important role in many environmental and energy applications, such as water desalination, electrochemical energy storage, and energy storage. Water-induced electrostatic interactions drive the chemical processes behind these technologies, as their ability to quantify the interactions between graphene, ions, and charged molecules is of paramount importance in designing more efficient and effective iterations.

“Every time you interact with ions in matter, the medium is very important. Water plays a vital role in mediating interactions between ions, molecules, and interfaces, which creates many natural and technological processes,” said Monica Olvera de La Cruz, head of research. Science and Engineering teachers. “However, we don’t understand much about how water interactions affect nanofinance at the nanoscale.”

Graphene-Water Interface

Illustration showing the interaction between ions at the graphene-water interface. Credit: Northwestern University

Using computer modeling simulations in Northwestern engineering and Argonn’s ray reflectivity experiments, the research team investigated the interaction between two oppositely charged ions in water in different positions bounded between two graphene surfaces. They saw that the strength of the interaction was not equivalent when the ion positions were exchanged. This symmetry rupture that researchers called non-reciprocal interactions is a phenomenon that electrostatic theory did not predict before.

The researchers also found that the interaction between oppositely charged ions became disgusting when one ion was introduced into the graphene layers, and the other was absorbed at the interface.

“From our work, it can be concluded that water structures alone cannot determine the effective electrostatic interactions between ions near interfaces,” said Felipe Jimenez-Angeles, principal investigator and researcher at the Northwestern Center for Materials Computing and Theory. “The lack of reciprocity we have seen means that the ion interactions at the interface do not meet the isotropic and translational symmetries of Coulomb’s law and can be present in both polarizable and polarizable models. This asymmetric polarization of water understands ion separation mechanisms such as ion selectivity and ion specificity “.

“These results show a different layer of how ions interact with interfaces,” said Paul Fenter, team leader and team leader at Argonne’s Chemical Science and Engineering Division, who led the radiographic measurements of the research using Argonne’s Advanced Photographic Source. “Significantly, these approaches are derived from simulations validated through experimental observations for the same system.”

These results may affect the design of membranes for selective ion adsorption used in environmental technologies, such as water purification processes, batteries and capacitors for electrical energy storage, and biomolecules, proteins, and DNA.

Understanding the interaction of ions can have an impact on advances in neuromorphic computing, as computers function like the human brain in a more efficient way than complex computers today. Lithium ions can achieve plasticity, for example, by inserting or removing layers of graphene from neuromorphic devices.

“Graphene is the perfect material for devices that emit signals through ion transport in neuromorphic applications,” said Olvera de la Cruz. “Our research has shown that the interactions between ions intercalated in graphene and ions physically absorbed in the electrolyte are disgusting and affect the mechanics of these devices.”

The research has provided researchers with a fundamental understanding of electrostatic communications in the intermediate range that are close to the interfaces that transcend its relationship with water graphene, as it is essential to study other processes in physics and science.

“Graphene is a regular surface, but these findings may help explain electrostatic interactions in more complex molecules, such as proteins,” Jimenez-Angeles said. “We know that what is inside the protein and the electrostatic charge outside it is important. This work provides us with a new opportunity to explore and analyze these important interactions. ”

Reference: Felipe Jiménez-Ángeles, Katherine J. Harmon, Trung Dac Nguyen, Paul Fenter and Monica Olvera de la Cruz, non-interactive interactions caused by water confinement ”, November 17, 2020, Physical Examination Research.
DOI: 10.1103 / PhysRevResearch.2.043244

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