Solid Oxide Fuel Cell Materials for Aerospace Applications

Abstract

This Ph.D. thesis explores the integration of Solid Oxide Fuel Cells (SOFCs) into aviation propulsion systems, focusing on their potential to address sustainability challenges in the aviation sector. SOFCs offer high energy efficiency, reduced emissions, and adaptability to various fuels, aligning with aviation’s environmental goals. The lightweight and compact nature of SOFC systems makes them suitable for integration into aircraft.

Aviation integration requires the technical, operational, and regulatory aspects to be addressed. Responsive SOFC systems with efficient power management and thermal cycling durability are essential. Miniaturization, weight optimization, and safety compliance are crucial for aviation. Navigating regulations and certification processes is also vital.

Beyond emissions reduction, SOFCs can mitigate noise pollution near airports through quieter operation and all-electric or hybrid-electric propulsion. Research suggests that SOFC integration could transform air travel into a cleaner and more sustainable mode.

Fuel cells, in particular solid oxide fuel cells (SOFCs), hold promise for various applications due to their efficiency and cleanliness. This study investigates SOFC integration into propulsion systems, comparing ammonia and hydrogen fuels. Efficiency, emissions, and advantages over proton exchange membrane fuel cells are assessed. Harnessing waste heat to improve efficiency is also explored.

Results show superior efficiency for SOFC configurations (ammonia fueled: 62%, hydrogen fueled: 61.5%, and proton-exchange membrane (PEM) fuel cell: 56%), with a thermoelectric generator enhancing efficiency by 10%. However, to fully leverage these advantages, addressing manufacturing challenges is crucial. For this reason, different fabrication methods are investigated to understand their advantages and shortcomings.

The core focus of this research revolves around the barium zirconate cerate yttrate (BZCY) electrolyte, driven by its many advantages in contrast to other electrolyte options within the realm of solid oxide fuel cells. A range of synthesis and fabrication methods are explored such as sol-gel synthesis, solid state route, and cold sintering.

Sol-gel synthesis is conventionally used to reduce the sintering temperature of SOFC electrolyte materials, subsequently reducing the energy required to fabricate them. This study shows that, while controlled reactions yield promising results, challenges in structural integrity and phase stability remain.

Solid-state fabrication of BZCY electrolytes instead reveals desirable properties (maximum ionic conductivity of 10−1 S/cm at 600 °C and 10−3 S/cm at 200°C), however, the high sintering temperatures make this method one of the most energy consuming.

Cold sintering reduces the overall energy consumption of the fabrication process by nearly 50%, while maintaining similar conductivity levels (10−3.7 S/cm at 200°C) despite higher precursor costs.

Process parameters, microstructure, energy consumption, and cost considerations are vital for sustainable and effective fabrication. This research lays the groundwork for SOFC integration in aviation and explores advanced materials and fabrication methods to enhance efficiency and sustainability.

Date of Award	2 Oct 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Chris Bowen (Supervisor), Frank Marken (Supervisor) & Tom Fletcher (Supervisor)