FIRST-PRINCIPLES COMPUTATIONAL STUDY OF FAST PROTON-CONDUCTING OXIDES.

Solid ceramic proton conductors are a crucial component for hydrogen-based energy devices, such as solid oxide fuel cells, electrolyzers, hydrogen separation membranes, and novel electronic computing devices. I performed first-principles computation to systematically investigate a wide range of perovskite and double perovskite materials and to reveal the effects of different cations and their combinations on the proton diffusion and hydrogen incorporation to rationally guide the future development of these perovskite proton conductors. The high-throughput computation discovered a number of layered double perovskite materials with good proton incorporation capability and fast proton diffusion. The results provided the design principles for the cation mixing in perovskite proton conductors and provided new research directions for novel double perovskite proton conductors for novel energy or electronic devices. I performed first-principles calculations to reveal the atomistic mechanisms of proton insertion and diffusion in SrCoO2.5 (SCO) brownmillerite structure that was reported as a fast proton conductor than typical perovskite-based oxide proton conductors. By studying the hydrogenated brownmillerite SCO in a range of H concentrations, first-principles calculations revealed the proton diffusion mechanisms in brownmillerite which give rise to faster proton diffusion than in perovskites proton conductors. The understanding of fast proton conduction mechanisms in brownmillerite provided insight into the future development and discovery of novel proton conductor materials. I performed a systematic first-principles computation study on a wide range of ternary oxide materials to understand the role of cations and compositions on materials stabilities and proton conduction in order to identify new proton conductor materials. By analyzing a large set of computation data generated on a wide range of oxide materials with different chemical compositions, our computation revealed how the mole fraction and the species of cations affect water stabilities and hydrogen insertion. By studying the proton diffusion in many different materials, our proton diffusion analysis showed that oxide materials with connected BO6 octahedra are optimal for fast proton diffusion. Following our materials understanding, our high-throughput computation identified a dozen oxide materials with good water stability, good proton incorporation capability, and fast proton diffusion. This thesis provided a fundamental understanding and design principles to develop oxide proton conductor materials with good stabilities