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Persistent URL http://purl.org/net/epubs/work/63434969
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Record Id 63434969
Title Understanding the Proton Transport in a Barium-Based Perovskite: From Incorporation to Dynamics.
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Abstract Proton-conducting solid oxide fuel cells (PCFCs) are considered a promising next generation energy conversion technology due to their high efficiency and compatibility with hydrogen as a clean fuel. Among the various candidate materials, the barium-based perovskite BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711) system has attracted significant attention because of its outstanding proton conductivity. However, despite extensive studies on its electrochemical performance, the fundamental origin of its exceptional conductivity has not been systematically investigated. This lack of mechanistic understanding hampers the rational design of improved PCFC materials. In this thesis, a systematic multi-scale experimental strategy was developed to elucidate the mechanisms underpinning the outstanding performance of BZCYYb1711. The approach centred on assessing the impact of hydration annealing on proton dynamics, with particular emphasis on its relationship to crystal structure, chemical composition, proton incorporation, and both localised and long-range transport processes. Structural evolution was examined using high-temperature X-ray diffraction (HT-XRD), while the chemical composition was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS). Proton incorporation was quantified through thermogravimetric analysis (TGA) and neutron-based methods, including prompt gamma activation analysis (PGAA), providing direct measurements of mobile proton concentrations within the lattice. Transport dynamics across multiple timescales were further investigated using neutron Compton scattering (NCS), quasielastic neutron scattering (QENS), and electrochemical impedance spectroscopy (EIS). Together, this integrated methodology established a direct connection between hydration-induced proton uptake, microstructural modifications, and proton dynamics spanning both localised and long-range regimes. Based on the comparison of incorporated proton concentrations between the as-calcined sample (BZCYYb-cal) and the humid-annealed sample (BZCYYb-HA), a novel phenomenon was discovered: BZCYYb1711 can incorporate a significant amount of protons directly from the environment, even without intentional humid annealing. This challenges the long-standing assumption in the PCFC field that proton incorporation relies almost exclusively on deliberate humidification and therefore represents a major conceptual advance in understanding proton behaviour in perovskite electrolytes. Complementary insights from HT-XRD and NCS further revealed that humid annealing induces anisotropic changes in the lattice parameters, which may alter the localised force field experienced by protons. This structural effect was reflected in QENS results, which showed a change in the localised proton hopping frequency in the hydrated sample, Though establishing a direct bridge between localised dynamics and macroscopic conductivity remains challenging. The findings of this PhD study demonstrate that the exceptionally high conductivity of BZCYYb1711 arises from its ability to intrinsically incorporate a significant amount of protons, even without deliberate humid annealing. In addition, the localised lattice distortions introduced by humid annealing were shown to facilitate the proton hopping, offering a potential strategy for designing new systems with optimised proton dynamics. Beyond elucidating the mechanisms in BZCYYb1711, this thesis establishes a transferable framework for systematically investigating proton transport in other proton-conducting oxides. This approach not only deepens the fundamental understanding of proton conduction but also provides a rational basis for the development of next generation PCFC electrolytes with enhanced performance.
Organisation ISIS , ISIS-VESUVIO , STFC
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Licence Information: Creative Commons Attribution 4.0 International (CC BY 4.0)
Language English (EN)
Type Details URI(s) Local file(s) Year
Thesis PhD, Department of Materials, Imperial College London, 2025. 2025