Bailey, Joshua James; (2019) Monitoring the Microstructural Evolution of Solid Oxide Fuel Cell Anodes. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

As the global energy landscape evolves in the face of climate change, the uptake of intermittent renewables is gaining ground. Electrochemical devices for energy generation and storage are therefore becoming increasingly prevalent. Solid oxide fuel cells represent an energy conversion device with high efficiency and fuel versatility but continue to suffer from cost and durability issues, hindering commercial viability. Establishing electrode microstructure-property relationships provides insight into both initial and long term performance and thus far, full comprehension of degradation phenomena has remained elusive. Building on 2D stereological approaches, recent advances in tomographic techniques such as focused-ion beam-scanning electron microscopy and X-ray nano computed tomography have allowed for 3D investigations of electrode microstructures. However, the former methodology is inherently destructive and with the latter, reliable contrast for typical SOFC electrode materials has not been easily accessible. In this thesis, an examination of these tomographic modalities is conducted, with focused-ion beam scanning electron microscropy slice and view applied to both virgin and aged Ni-YSZ anodes to virtually reconstruct their microstructures. A laser-preparation technique for the fabrication of geometrically optimised samples for X ray nano-computed tomography is developed, and facilitates access to a larger sampled volume, thus providing more representative characterisation of the entire anode. Prepared samples are exposed to ex-situ annealing in a lab-based furnace wherein 900 °C is identified as the appropriate temperature for monitoring appreciable microstructual evolution within the first 12 hours of annealing. An in-situ¬ laser heating set-up at a synchrotron beamline illustrates the very early-stage microstructural reorganisation inherent to high-temperature operation. Significant attention is directed throughout towards the extraction of reliable metrics, sampling a representative volume element and capturing evolution by digital volume correlation techniques. The expectation is that the developed methodology will provide insight into the necessary fabrication and operational parameters for maximising solid oxide fuel cell performance and durability.

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