Dissertation Title: In Situ Investigation and Modulation of Hydroxyl Proton Chemical Environment in Proton Conducting Oxides
Date: 2025/07/30 – 2025/07/30
Dissertation Title: In Situ Investigation and Modulation of Hydroxyl Proton Chemical Environment in Proton Conducting Oxides
Speaker: Zihan Zhao, Ph.D. candidate at UM-SJTU Joint Institute
Time: 10:00-12 p.m., July 30, 2025 ( Beijing Time)
Abstract
Improving the proton conductivity of proton-conducting oxides at intermediate to low temperatures (below 400 °C) remains one of the key issues for advancing protonic ceramic fuel cells (PCFCs). Current optimization strategies face challenges due to the complex influence of doping on microchemical properties. Investigations into how material modifications affect hydroxyl proton behavior remain preliminary, particularly across various environmental conditions. This dissertation investigated the impact of the chemical environment surrounding hydroxyl protons on proton concentration and mobility in situ. This study explored the hydroxyl and oxygen species, local lattice structure, and hydrogen bond characteristics in proton conductors to propose strategies for improving conductivity at intermediate to low temperatures.
Firstly, the hydroxyl proton and oxygen behavior in conventional perovskite electrolytes, BaZr0.9Y0.1O3−δ and BaCe0.9Y0.1O3−δ, were explored. Through in situ near-ambient pressure X-ray photoelectron spectroscopy, oxygen species were analyzed under operating conditions. Applying an external potential further promoted hydration by increasing hydroxyl groups and undercoordinated oxygen species, facilitating proton conduction. These findings highlighted the changes in the oxygen chemical environment through environmental and electrical modulation.
Secondly, a novel-type perovskite (BaSc1–xMoxO2.5+3x/2, BSM) was examined, with heavily doped Sc3+, high proton conductivity, and low activation energy (0.3 eV). BSM25 exhibited lower proton concentration but higher proton diffusivity than BSM20, as measured by conductivity and isotope exchange experiments. Through in situ Raman spectroscopy, the local lattice asymmetry and proton–proton interactions were observed to impede proton transport, particularly at lower temperatures. This work identified lattice symmetry optimization and reduction of carrier-blocking effects as critical directions for enhancing proton transport at intermediate temperatures.
Thirdly, to extend applications to lower temperatures, surface protonic conduction was investigated in porous nanocrystalline TiO2 using in situ Raman spectroscopy. Quantitative analysis distinguished molecular and dissociative adsorbed water concentrations. The different temperature regions from low to high corresponded to the surface proton conduction from the vehicle mechanism, to hopping within molecular adsorbed water layer, and then to the typical proton hopping mechanism. Surface adsorbed water is more extensive in wet N2 than in wet O2, suggesting that the surface reduction modification can further improve surface proton conductivity.
In conclusion, this dissertation reveals fundamental mechanisms by which the chemical environment governs proton concentration and transport. Through in situ targeted modulation with environmental conditions, it is possible to enhance proton concentration or optimize the local chemical environment to facilitate proton transport, thereby improving proton conductivity, apart from altering the material composition. These findings advance the development of proton-conducting oxides to low temperatures, offering practical pathways to enhance conductivity and improve the performance of PCFCs.
Biography
She received her bachelor degree from Shanghai Jiao Tong University in 2020. Now, she is a Ph.D. candidate student at the SJTU Global College, supervised by Prof. Qianli Chen, major in mechanical engineering. Her research focuses on how the chemical environment of hydroxyl protons affect the proton conductivity of proton conducting oxides. She has published 4 papers, including 2 first author papers, and have another 2 papers in preparation. She participated in 6 academic conferences, including 3 oral reports and 3 poster exhibitions. She has completed the courses required by the graduate training plan and obtained the required academic qualifications.