Date of Award
Doctor of Philosophy (PhD)
School of Materials Science and Engineering
Kyle S Brinkman
Luiz Gustavo Jacobsohn
Protonic ceramic conductors are the key component in a wide range of protonic ceramic electrochemical devices. Such as protonic ceramic fuel cells, electrolysers, sensors, and hydrogen pumps. The widely studied protonic ceramic conductors are perovskite-structure oxides with high proton conductivity and chemical stability at high temperatures. However, the performance of perovskite-based protonic ceramic conductors dropped rapidly at low temperatures due to the blocking effect of grain boundary. Different from the blocking effect in perovskite membranes, the interface works as an alternative pathway for proton transport in nanostructured simple oxide systems, relying on the chemisorbed and physiosorbed water on the interface. This phenomenon provides a new strategy to design a new type of protonic ceramic conductors through interfacial engineering at the nanoscale on perovskite-based protonic ceramic conductors. This designed membrane demonstrated a combined “interfacial effect” and “bulk effect” for proton transport. This dissertation is focused on the role of interface for proton transport, including solid-solid, solid-liquid interface and phase boundaries in protonic ceramic fuel cells. In Chapter 3, the role of interface for proton transport on perovskite-based protonic ceramic conductors was studied by using BaZr0.8Y0.2O3-δ as an example. The blocking effect of grain boundary was revealed by the conductivity measurements under different atmospheres. A new strategy based on the anions doping on oxygen lattice was performed to improve both the bulk and grain boundary properties for proton transport. In Chapter 4, the role of interface for proton transport in simple oxide-based protonic ceramic conductors was studied by using nanostructured TiO2 as an example. Comparing to perovskite-based protonic ceramic membranes, proton transport in the interface of simple oxide membranes showed higher proton concentration, and higher proton mobility which indicates a higher proton conductivity at low temperatures. This study showed the interface can be used as a new pathway for proton transport at low temperatures in contrast to conventional wisdom of interfacial blocking effect observed in high temperature ionic conductors. In Chapter 5, nanocrystalline perovskite membranes were developed by creating more interface areas, in which proton transport not only through the bulk materials, but also in the absorbed water layers at the interface. The enhanced proton transport properties, like the proton concertation, proton mobility, and proton conductivity were achieved in nanocrystalline BCZYYb, indicating a combined “interfacial effect” and “bulk effect” for proton transport at low temperatures. This improvement showed a new promising solution for the development of advanced ionic conductors. In Chapter 6, high performance protonic ceramic fuel cells were developed based on the strategies mentioned above, including anions doping, interface engineering at the nanoscale. In addition, phase boundary (anode/electrolyte) in protonic ceramic fuel cells was designed by a one-step phase inversion method. Comparing to the conventional one, the power density of protonic ceramic fuel cells with designed anode microstructure nearly doubled at 600 °C, indicating the time and energy-saving process developed in this study showed great promise for the fabrication of high performance protonic ceramic fuel cells. In summary, the interface in protonic ceramic conductors plays an important role on proton conduction, including water absorption ability, proton mobility, proton conductivity, hydrogen isotope exchange coefficients, and the proton transport mechanism. A better design of materials’ interface, either in the solid-solid interface and solid-liquid interface could dramatically increase the performance of protonic ceramic conductors and protonic ceramic fuel cells.
Gao, Jun, "The Development of High-Performance Protonic Ceramic Conducting Membranes by Interfacial Engineering" (2021). All Dissertations. 2854.