Multiscale Analysis and Design of Solid Oxide Fuel Cells for On-orbit Space Power

Aaron Bain, December 13, 2022

Constraints on modern spacecraft electrical power delivery are created by the overall lack of gravimetric energy density in modern batteries and in particular the inability for solar panels to deliver high power output for a prolonged period of time. To reduce these constraints, this research study seeks to design a solid oxide fuel cell (SOFC) system which will consume onboard bipropellants usually reserved for on-orbit maneuvering thrusters and enhance current fuel cell materials technology to enhance performance and ensure against degradation. Atmosphere independent fuel cells have higher theoretical specific energy than batteries, even considering developments in the next decade (eg. hydrazine/NTO pairing has nominally over 11 times the specific energy of primary lithium sulfate batteries, 1.65 kWh/kg vs 0.148 kWh/kg respectively). Dynamic modeling will elucidate system components and operation critical to safe, efficient power delivery of such a high temperature fuel cell. However, for usage of SOFCs to be feasible, certain disadvantages, such as their high operating temperature, electrochemical losses, and high cost of manufacturing, must be solved. In particular, the field of materials research has a unique position of being able to quickly and simultaneously solve many of these issues through the development of material structures that do not currently exist commercially. The microstructures present in SOFC electrodes play a vital role in improving overall cell performance. To that end, a theoretical effective-medium model has been created to facilitate the design of 3D printed electrodes. This model factors in microstructure parameters, mass transfer, ionic and electrical transport, and gas-surface electrochemical reactions inside the electrodes. The technique of functional material grading, which has begun to see wide research and commercial usage for such problems as acoustic impedance matching, thermal control, and mechanical design has been leveraged for the enhancement of fuel cell electrodes. Multiobjective optimization of the effective-medium model reveals functional grading profiles which would be useful for enhanced performance and stability for long-term fuel cell usage. The interplay of system design and material component design serves as a template for future aerospace design studies.