| Summary: | Future implantable medical devices such as sensors, drug delivery systems, and electroceuticals require efficient, reliable, and highly miniaturized power sources. To date, the predominant power source of implants is the Li–I2 pacemaker battery, which is limited in its scale-down potential without sacrificing capacity. Therefore, new power sources for implantable devices are needed. In this thesis, a ceramic-electrolyte glucose fuel cell is invented, which constitutes the smallest potentially implantable glucose fuel cell to date. By use of the ceramic proton-conducting electrolyte ceria and a free-standing membrane device architecture, the novel ceramic-electrolyte glucose fuel cell can be scaled down to a thickness below 400 nm. The ceramic-electrolyte glucose fuel cell is biocompatible by materials choice, and unlike polymer-electrolyte glucose fuel cells, can be easily thermally sterilized for future implantation. This thesis demonstrates fabrication, fundamentals and the performance of the first ceramic-electrolyte glucose fuel cells, with a power density of up to 43 µW cm−2, and shows unusually broad performance statistics across 150 devices thanks to a custom-designed measurement apparatus. A fundamental property required to realize such glucose fuel cells was to define a proton-conducting ceramic thin film electrolyte. Therefore, beyond device design and development, this thesis explores the proton transport properties of ceria. Through a ceria model system deposited via wet-chemical spray pyrolysis, sufficient proton conductivity is observed. Moreover, slow hydration kinetics, at the order of several days, is detected in ceria, which could explain the large discrepancies of observed proton conductivity in the literature to date. Finally, the structural properties of ceria deposited through spray pyrolysis are studied under various thermal processing conditions, providing guidelines on the cost-effective processing of ceria as a proton-conducting electrolyte. Here, it is found that Raman spectroscopy can be employed to observe texture evolution in ceria thin films, which is relevant for both glucose fuel cells and other catalytic applications. Overall, this thesis constitutes a study of the processing, structure, proton transport, and device development of ceria, resulting in nano-scale ceramic-electrolyte glucose fuel cells that could enable the next generation of miniaturized implants.
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