Degradation Mechanisms of Oxide Ceramics Under Molten Regolith Electrolysis Conditions

Citation

Yu, Kevin (2026) Degradation Mechanisms of Oxide Ceramics Under Molten Regolith Electrolysis Conditions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/41bv-7696. https://resolver.caltech.edu/CaltechTHESIS:12042025-001904943

Abstract

Molten regolith electrolysis (MRE) is a promising in situ resource utilization process that produces both metals and O₂ through the direct electrolysis of molten lunar regolith (dirt), in support of a permanent human presence on the Moon. However, MRE requires an operational temperature of 1600°C, involves contact with corrosive molten regolith, and causes an oxidizing atmosphere during electrolysis. These conditions prevent the usage of many refractory materials due to rapid degradation. Moreover, there are additional challenges associated with MRE, such as bubble detachment and O₂ collection at the anode.

In this thesis, a hollow anode design, composed of an oxygen-conducting yttria-stabilized zirconia (YSZ) shell and a platinum current collector, is presented to address the challenges of MRE. Research is performed to evaluate the performance of YSZ electrolytes and containment materials in the extreme MRE environment and identify the mechanisms governing their degradation. From these experiments, a laboratory-scale MRE cell is designed and fabricated to support hollow anode testing. Electrolysis experiments with lunar regolith simulants successfully demonstrate sustained oxygen production for up to 12 hours. Extended testing with a degradation mitigation strategy further increases O₂ production efficiencies and enables cumulative operation of 40 hours, establishing design life estimates for YSZ hollow anodes and guidelines for integration into industrial-scale MRE systems.

A previously unreported Sc₂O₃-rich phase, silicon aluminum scandate (SAS), is discovered while performing materials compatibility testing. The crystal structure of SAS is solved using microcrystal electron diffraction, and its material properties are characterized. These results indicate that SAS is an entropy-stabilized oxide with potential applications as a thermally insulating, refractory oxide material.

Ultimately, the work presented demonstrates the feasibility of YSZ hollow anodes for MRE and expands the understanding of ceramic behavior in molten oxide environments. The successful production of O₂ with a hollow anode provides a foundation for scaling MRE toward industrial operation on the lunar surface, while the discovery of SAS highlights the potential for uncovering new oxide materials in extreme environments.

Thesis Files