NSF-DFG Confine: Aqueous Electrolytes in Nanoporous Media: Structure, Dynamics and Electrochemo-Mechanical Actuation

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When salts dissolve in water, they form electrolytes. Near a charged solid surface ions in an electrolyte redistribute, forming an electric double layer (EDL). EDL plays an important role in geochemical and biological processes and is utilized in technologies for electrochemical energy storage. While the structure and properties of EDL are well understood for an EDL near a planar surface, understanding of EDL in nanoporous materials is poor. These nanoporous materials are of interest for electrochemical energy storage applications, which motivates this project. In particular EDL formation in nanoporous materials causes mechanical stresses and lead to materials deformation. This research project aims to quantify the formation of EDL in aqueous solutions of electrolytes in nanoporous materials and relate it to stresses and strains in these materials. The knowledge gained from this research could contribute towards developing new electrochemical energy storage devices, such as supercapacitors with green, water-based electrolytes, as well as actuators based on electrochemical principles. This project will contribute to improved STEM education through the inclusion of research related topics in the undergraduate courses taught at the university. During the summer months high school interns will work on projects related to this research. The objective of this research project is to apply experiments on the micro- and macroscale along with molecular simulations to gain fundamental understanding of the electromechanical properties of an EDL in nanoporous media. Electrically conducting nanoporous carbons with high specific surface area, well-defined pore sizes (1-10 nm) and pore geometries will be synthesized. Different surface chemistries (hydrophobic vs. hydrophilic) will be introduced. Depending on the applied electrical voltage between electrolyte and solid, the surface chemistry and the pore diameter, EDL formation and mechanical actuation in the material will be investigated. Synchrotron-based X-ray scattering will be used to study the EDL in-operando, with special attention to the charge/discharge and thus ion transport kinetics. Molecular dynamics simulations will be employed to represent the structural properties of the surface of the nanoporous medium and the electrolyte. Combination of experiments (German team) and simulations (US team) will help to derive the structural, thermodynamic and transport properties of the geometrically confined electrolyte and their role for electrochemo-mechanical coupling at the scale of a single pore and the entire porous sample. In addition to these fundamental insights into aqueous electrolytes in geometric confinement, this study can potentially contribute to development of new generations of electrochemical devices.This project was awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.