March 23, 2012
Title: Solid-State NMR Studies of Ion Dynamics in Materials for Energy Storage and Conversion
Abstract: Hydrogen bonding plays a critical role in candidates for proton-exchange membrane fuel cells (PEM-FCs) , as it provides the network necessary proton transport. The utility of solid-state 1H NMR under fast magic angle spinning to elucidate both structure and dynamics of such materials is illustrated here. The hydrogen-bonding network must be both pervasive and dynamic in order for long-range proton transport to be achieved. The structural motifs must be understood, and moreover, the lattice energies in the structure must be low enough to allow rearrangement and mobility. To this end, several classes of proton-conducting materials have been investigated, including Nafion composite membranes, as well as novel imidazole based polymers and solid-acid candidates. The primary goal is to establish proton conducting mechanisms, and correlate the microscopic observables, obtained by NMR, with the macroscopic performance of the membranes.
Similar to the critical role played by protons in PEM-FCs, lithium ion transport governs the performance of lithium ion batteries. In recent years, the lithium vanadium phosphate and fluorophosphate intercalation compounds have been investigated as cathode materials for lithium ion batteries. Both classes of materials demonstrate promising electrochemical performance with high cycling capacities and structural stability comparable to the widely studied olivine LiFePO4. Vanadium fluorophosphates in particular, relative to the vanadium phosphates, have shown higher V-redox potentials attributable to the additional contribution to the inductive effect of the phosphates from the fluorine atoms. While many details regarding the structure of the host lattice are available, very few details regarding the behaviour of the mobile ion have been presented. Here we evaluate the timescales and energy barriers of Li-ion hopping in a series of these compounds using 6Li MAS NMR techniques.
Biography: Dr. Gillian Goward leads an active research team at McMaster University, with research interests spanning materials science, physical chemistry, electrochemistry, and spectroscopy. She completed her Ph.D. in Chemistry at the University of Waterloo in 2000. Her thesis work involving the development and characterization (using both electrochemical and NMR methods) of novel anode materials for Lithium Rechargable Batteries was supervised by Profs. Linda Nazar and Bill Power. Following graduation, she worked as a post-doctoral fellow in the group of Prof. H. W. Spiess at the Max Planck Institute for Polymer Research in Mainz, Germany. Her work there involved applications of advanced NMR techniques to study novel proton-conducting materials as candidates for polymer exchange membranes in fuel cells and was funded by an NSERC post-doctoral fellowship. Since July 2002, she was appointed Assistant Professor of Chemistry at McMaster University in 2002, and promoted to Associate Professor in 2007. She was a recipient of the Premier's Research Excellence Award in 2003, supported by the Ontario Government and General Motors of Canada. Her research team is working on solid-state NMR and electrochemical materials.