Defect Chemistry and Protonic Conductivity of Polymer-Templated Mesostructured Thin Film Oxide Ceramics and Nanocomposites

• Applicants: Dr. Torsten Brezesinski; Dr. Matthias Thomas Elm
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 360678694

• Final Report Year: 2022

Final Report Abstract

The primary goal of the project was to examine the influence of the high surface area of mesoporous metal oxide thin films on the ionic, electronic and protonic transport properties. In addition, the project was focused on preparing and characterizing nanocomposites by coating the free surface of the aforementioned thin films using atomic layer deposition. Analysis of the transport properties of block-copolymer-templated mesostructured YSZ thin films showed that the conductivity is more or less independent of pore size. For the first time, a dominant electronic conductivity was observed for YSZ thin films under highly reducing conditions, arising from the formation of a surface space-charge region where the electrons are accumulating. These results demonstrate the profound effect that the free surface has on the defect chemistry in porous materials. Surface modification via atomic layer deposition allowed significantly improving the thermal stability of mesoporous metal oxides, thereby extending the range of potential applications in the field of energy. Apart from that, the latter can be exploited to design mixed-conducting nanocomposites, as shown for polymer-templated mesostructured YSZ thin films with a nanoscale CeO2 coating. Electrical characterization revealed that the electronic conductivity of CeO2/YSZ nanocomposites strongly depends on the coating thickness. It was also demonstrated that surface coating greatly affects the protonic conductivity. Taken together, the results pave the way for the rational development of nanostructured oxide ceramics with tailored (ionic, electronic and protonic) conductivity. Finally, a network model was developed, which allows the simulation of the impedance of such materials by accounting for the realistic micro- and nanostructure. Preliminary data indicate that additional contributions may arise in the impedance, which are not related to microscopic transport processes. Instead, they occur because of changes in the dominant current paths with excitation frequency.

Publications

• “Thin films of thermally stable ordered mesoporous Rh2O3(I) for visible-light photocatalysis and humidity sensing” ACS Appl. Nano Mater. 2, 7126 (2019)
  L.A. Dubraja, D. Boll, C. Reitz, D. Wang, D. Belić, A. Mazilkin, B. Breitung, H. Hahn, M.T. Elm, T. Brezesinski
  
• “Atomic layer deposition of nanometer-sized CeO2 layers in ordered mesoporous ZrO2 films and their impact on the ionic/electronic conductivity” ACS Appl. Nano Mater. 3, 10757 (2020)
  P. Cop, E. Celik, K. Hess, Y. Moryson, P. Klement, M.T. Elm, B.M. Smarsly
  
• “Tailoring the protonic conductivity of porous yttria-stabilized zirconia thin films by surface modification” Phys. Chem. Chem. Phys. 22, 11519 (2020)
  E. Celik, R.S. Negi, M. Bastianello, D. Boll, A. Maziklin, T. Brezesinski, M.T. Elm
  
• Ordered mesoporous metal oxides for electrochemical applications: correlation between structure, electrical properties and device performance“ Phys. Chem. Chem. Phys. 23, 10706 (2021)
  E. Celik, Y. Ma, T. Brezesinski, M.T. Elm
  
• “High-entropy energy materials: challenges and new opportunities” Energy Environ. Sci. 14, 2883 (2021)
  Y. Ma, Y. Ma, Q. Wang, S. Schweidler, M. Botros, T. Fu, H. Hahn, T. Brezesinski, B. Breitung
  
• “Understanding the impact of microstructure on charge transport in polycrystalline materials through impedance modelling” J. Electrochem. Soc. 168, 090516 (2021)
  J.K. Eckhardt, S. Burkhardt, J. Zahnow, M.T. Elm, J. Janek, P.J. Klar, C. Heiliger