NMR Insights into Fast Ion Conductors
P.-H. Chiena, X. Fenga, X. Lia, , J. Zhenga, M. Tanga, Y–Y. Hu a,b
a Dept. of Chemistry & Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, FL, USA 32306
b The National High Magnetic Field Laboratory, 1800 E. Dirac Drive, Tallahassee, FL, USA 32308
Fast ion conductors, also known as solid electrolytes, are widely used in energy storage technologies, including fuel cells, batteries, and sensors. New Li-ion conductors with high ionic conductivities have been “virtually” synthesized with computational efforts, panoramic synthesis strategies are necessary to effectively harvest the fruits. In our study, high-temperature in situ solid-state NMR is employed to follow the phase evolution and property changes of precursors, intermediates, and target compounds during the synthesis of fast Li-ion conductors. The interplay of thermodynamics and kinetics during the solid-state synthesis of fast ion conductors is also explored.
Ionic conductivity is determined by three factors, i.e., charge carrier concentration, ion dynamics, and ion transport pathways. Charge carrier concentration is affected by accessible Li sites, which are probed and quantified by Li NMR. Synthesis strategies are developed to increase the fraction of functional Li sites. Changes in Li NMR relaxation times with temperature have been measured, which reveal the motional rates and activation energies of Li ion dynamics. So far, the determination of Li-ion transport pathways has been mostly carried out with DFT calculations, while experimental studies are limited by the challenges to follow Li ion diffusional movement in complex systems. A solid-state NMR approach is devised on the basis of 6Li/7Li isotope replacement induced by a biased electric potential to determine Li ion transport pathways . This method was demonstrated on a few fast Li ion conductors. In summary, this talk discusses the unique contributions made with advanced solid-state NMR in investigating various aspects of fast ion conductors, including panoramic synthesis, simultaneous determination of phase evolution and ion dynamics, and improvement of ionic conductivities.
- Zheng, J.; Tang, M.; Hu, Y.-Y*. "Lithium Ion Pathway within Li7La3Zr2O12-Polyethylene Oxide Composite Electrolytes" Angewandte Chemie International Edition, 2016, 55, 1-6.
From solution to the gas-phase. What can we learn on the structure, dynamics and distribution of biomolecules?
Department of Chemistry and Biochemistry, Florida International University
Recent innovations in speed, accuracy and sensitivity have established mass spectrometry (MS) based methods as a key technology for the mapping and analysis of small molecules, lipids, peptides, protein, DNA and DNA-protein complexes in biological systems. In particular, Ion Mobility Spectrometry – Mass Spectrometry provides a powerful tool for the identification of structural motifs, and when complemented with theoretical calculations, it permits a better understanding of the main motifs that drive the dynamics across the free energy landscape. We have recently introduced a Trapped Ion Mobility Spectrometry coupled to Mass Spectrometry (TIMS-MS) as a high-throughput technique for the study of conformational states of biomolecules, as well as the kinetic intermediates involved during their folding as a function of the molecular environment (e.g., pH, organic and salt content). While this description holds true for most contemporary IMS analyzers, the higher resolving power (e.g., R= 150-250, 3x larger than traditional IMS systems) and the unique ability to hold and interrogate molecular ions for kinetic studies (e.g., millisecond-second time scale) provides TIMS-MS with unique capabilities for the study and interrogation as a function of the time after desolvation. Recently combined with hydrogen-deuterium exchange, HDX-TIMS-MS, a more detailed description of the accessible surface area and the folding can be achieved over time. That is, HDX-TIMS-MS has a significant advantage in the flexibility to interrogate, at the single molecule level, the molecular interactions that define the conformational space. In the present talk, recent results that reveal the kinetic intermediates and the main folding pathways for small molecules, peptides, proteins, DNA and DNA-protein complexes will be discussed as well as some novel chemical mapping strategies at the single cell level.
Quantum Chemistry without Wave Functions
A. Eugene DePrince, III
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390
Quantum-chemical computations have become an indispensable and routine component of modern chemical research. However, certain classes of chemical problems require such a sophisticated treatment of the electronic structure that computations become infeasible for large systems. Recent advances in electronic structure theory address the intractable complexity of such problems. I will discuss how one can abandon the wave function as the central variable in electronic structure theory in favor of the two-electron reduced-density matrix. In doing so, we can devise theories and algorithms that enable previously impossible computations on challenging systems.