Electrodeposition of Si in Molten Salt Toward In Situ Resource Utilization Research

Abstract

Electrodeposition of reactive metals such as Si from metal oxide in high temperature melt is one of promising methods for ISRU (in-situ resource utilization) on the moon and Mars for constructing a self-propagated PV power generation system. Our temporal goal is to provide metal electrodeposition on cathode and O2 gas generation on inert anode from mineral materials by molten oxide electrolysis. Preliminary experiments on mineral processing and molten salt electrolysis with regolith simulant with various elements had been engaged in our group. It is necessary to accumulate more fundamental thermodynamic and electrochemical properties of metallic or oxide ions in high temperature melt toward sustainable ISRU project. We report here the electrodeposition mechanism of Si from SiO2 in fluoride-based melt at quite lower temperature than the case of molten oxide in order to examine the interfacial phenomena between electrode surface and molten salt with simplified composition. Si dense film is electrodeposited at 10 times higher rate in the melt with addition of Li2O as a source of oxide ions. A high temperature Raman spectroscopy was applied to examine such a fast rate electrodeposition behavior. The fundamental terrestrial research on physicochemical interfacial phenomena encountered in power generation infrastructures, such as solar cells, fuel cells, and molten salt nuclear reactors, greatly contributes to developing the new frontier of high temperature science and technology for ISRU.