Unraveling Assembly and Charge Dynamics of Asymmetric Metal Complexes in Aqueous Solution

Dr. Yu Zhu, University of Akron (Principal Investigator)

Dr. Bryan Vogt, Pennsylvania State University (Co-Investigator)

The dynamics of ions in aqueous solutions tend to be considered as isolated hydrated ions, but the true complexity of these dynamics increases significant as the ion concentration in solution increases. At high concentrations, ions can pair and form clusters, which significantly impacts their mobility and charge transport characteristics. This phenomenon is particularly relevant to emerging needs in electrochemical energy storage, where high concentration provide efficiency.We have discovered new class of redox-active asymmetric metal complexes that exhibit significant enhancements in the water solubility. This increase solubility has been attributed to the modulation of the entropy of mixing, but these highly soluble metal complexes form large clusters in solution with no clear understanding of relationships between molecular structure, solubility and this nanostructure assembly. Here, we seek to develop fundamental understanding of how the molecular-level structure of asymmetric metal complexes controls the solubility, nanostructure formation and electrochemical characteristics. We will synthesize novel asymmetric metal complexes with a systematic variation in the symmetry numbers to facilitate basic insights into hypothesized symmetry-driven entropy effects that determine assembly and solubility. A suite of advanced characterization techniques, including small-angle X-ray scattering, small-angle neutron scattering, in-situ rheological SANS coupled with electrochemistry, cryo- and in-situ electrochemical TEM, and electrochemical methods, will be used to elucidate and probe the structures of these metal complexes formed in solutions at various scales. The overall objective is to provide fundamental mechanistic insights into the structure-property relationships of asymmetric metal complex electrolytes to control the charge storage and transport that lay the basis for understanding energy and power performance for aqueous electrochemical energy storage.