Key roles of point defects in porous assemblies of 2-D transition metal oxide nanosheets

Scott Misture
Alfred University
Online WebEx seminar
Thu, November 11, 2021 at 10:16 AM
Vanadium, manganese, and titanium oxides in their layered forms, and the 2-D nanosheets derived from such layered oxides, are of interest for electrochemical, photochemical and sensor materials. The impacts of point defects and nanostructure on charge transport, charge storage and catalytic properties have not been studied in detail for the exfoliated 2-D nanosheets, and we report direct links between charged defects and the electrochemical charge storage behavior. We focus our studies on 2-D nanosheets obtained by exfoliation of pristine particles with point defects on the metal sublattice introduced either before exfoliation by aliovalent doping or after exfoliation by varying suspension pH or gentle gas-phase reductions. Extensive characterization using synchrotron total scattering, X-ray spectroscopy and Raman spectroscopy are applied to understand the nature of the defects under ambient, in-situ and in-operando modes. Materials of interest include MnO2 and VO2, and the layered perovskite-related phases of the Ruddlesden-Popper, Dion-Jacobsen and Aurivillius families. The electrodes studied are prepared by electrophoretic deposition of flocculated nanosheets which form high surface area porous electrodes (200-300 m2/g), and we demonstrate that introduction of defects can improve charge storage capacity by factors of 3 or more, and improve charge transfer resistance by 10 times or more. The capacity fade in these materials is far better than for layered variants or typical nanoparticle electrode materials, which we attribute to the porous nature. In-situ synchrotron XRD and PDF, combined with in-situ XANES show that the chemomechanical response to charge/discharge differs in the nanosheet electrodes in that lateral expansion/contraction is easily accommodated to improve cycling stability.
Scott Misture
Dr. Scott Misture presently holds an Inamori professorship at Alfred University, having served on the faculty for 21 years. His earlier experience includes a few years at Oak Ridge National lab and time in Germany at Siemens Corporate Research. Misture’s research interests center on understanding how structure and defects define the properties of electrochemically and catalytically active oxides and oxide-metal interfaces. He develops and applies advanced in-situ and in-operando characterization tools to understand the effects of structure at the atomic scale and nanoscale, primarily X-ray and neutron scattering. His research has focused on oxides for energy conversion, including materials for high temperature fuel cells, as well as photocatalysts and oxides for electrochemical charge storage and related catalytic applications. Misture is engaged in the materials community as an editor for the Journal of Materials Research, past chair of the Board of Directors of the International Centre for Diffraction Data, and as a longtime officer and committee chair in the American Ceramics Society. He is also a member of the organizing committee of the Denver X-Ray Conference and holds or has held leadership positions in the American Crystallographic Association, the Materials Research Society, the National Academy of Sciences Committee on Crystallography and on advisory boards for neutron and synchrotron user groups and proposal evaluation panels. He also serves as Program Chair for three ABET-accredited degree programs at Alfred University including the programs in ceramic engineering, MSE and glass engineering science.