Quantification of Enhanced Ion-Pairing in Nanoconfined Electrolytes Using Valence-to-Core X-ray Emission Spectroscopy

Abstract

The increasing use of nanostructured materials in contact with aqueous solutions for various technological applications including energy storage requires an improved understanding of the effects of nanoconfinement. In this study, we use valence-to-core X-ray emission spectroscopy (VTC-XES) to quantify the effects of nanoconfinement on the evolution of local coordination structure of Zn complexes in aqueous zinc chloride systems. Recent work (Dhakal, et al., 2023) establishes the ability to quantify the Zn–Cl first shell coordination number. We find that ion pairing is enhanced in solutions under confinement in nanoporous carbon compared to their bulk counterparts, and we also find that the electrochemical voltage window (EVW) of such solutions is correlated to the extent of ion pairing. Several possible explanations for both the enhancement in ion pairing and its correlation with the EVW are discussed, with significant connection to the broader concept of water-in-salt electrolytes (WiSE).