(21c) Computational Study of Proton Behavior in Yttrium-Doped Barium Cerate

Effective ionic conducting materials are critical to the operation of several energy conversion devices, including batteries, fuel cells, and capacitors. The goal of this research is to explore the emerging field of nanoionics to understand and develop a new generation of ionic conducting materials. Nanoioncs focuses on manipulating the space charge layer at ionic interfaces to control ionic conduction. Barium cerate (BaCeO3) is a perovskite cerate that becomes an effective proton conductor when doped with an acceptor ion, such as yttrium, and hydrated. When this material is combined with palladium, a space charge layer with increased proton conduction capabilities is created. While proton conduction through these individual materials has been studied experimentally, there is a lack of molecular-level understanding of proton behavior within these ionic conducting materials. Using density functional theory (DFT) we modeled ionic transport behavior within yttrium-doped barium cerate (BCY) and at the interface between BCY and various hydrogen permeable metals. By understanding the mechanism of proton mobility through these hybrid materials, the ionic conduction properties of the materials can be manipulated and a more efficient and controlled method of material development can be achieved. Initial DFT studies have probed the effects of yttrium doping on proton behavior within bulk BCY material. Hydration enthalpy, entropy, and expansion have been calculated for various levels of yttrium doping. Consistent with published literature from experimental studies, we have found that hydration enthalpy becomes more negative with increased doping concentrations1. The yttrium dopant increases the basicity of the coordinated lattice oxygens, increasing the favorability of hydrogen bonding. Likewise, hydrogen entropy also becomes more negative with an increased concentration of dopant, which acts to stabilize protonic defects. Finally, hydration expansion increases slightly with increasing dopant levels. Comparable hydration expansion values have been reported for similar perovskite materials. Ultimately, this work has yielded basic insight into the influence of yttrium-doping on material hydration and proton behavior within BCY.