Electrochemical Oxygen Evolution from Metal Oxides Using Perovskite Anodes Towards Lunar Resource Utilization

Abstract

In-situ resource utilization (ISRU) has been proposed for realizing sustainable lunar development. One of the representative resources on the Moon is lunar regolith, which covers the lunar surface. The chemical composition of lunar regolith resembles the constituents of the Earth: silica (SiO2) is the most abundant oxides in the lunar regolith. Silicon, which can be produced by silica reduction, will be the material for solar cells, and oxygen is essential for manned space exploration. Enormous amounts of silicon and oxygen will be obtainable on the Moon without transportation from the Earth by establishing silicon reduction methods without consumables. However, the conventional silica reduction method consumes vast amounts of carbon, which cannot be mined on the Moon.For realizing carbon free silica reduction method consistent with the concept of ISRU, molten salt electrolysis processes using perovskite anodes has been researched. In this method, the silica dissolved in molten salts is electrolyzed using voltage with passage of direct current through electrodes, which generate oxygen gas and silicon by the electrochemical process. The perovskite oxides have high electrical conductivity and oxidation resistance. Therefore, the perovskite anodes have been expected as oxygen generation inert anodes.In this study, we report the characteristics of perovskite-type anodes for oxygen generation measured in the electrolysis experiments. In molten fluoride containing silica at a temperature over 500℃, the measured cyclic voltammograms with a perovskite-type anode show drastically increases of current density at 2.6 V vs K+/K, which was approximately same to the oxygen generation potential in the previous molten salt electrolysis result without the perovskite anodes. The characteristics of perovskite-type anodes for oxygen generation will be discussed from the results of electrochemical measurements and chemical analysis using XRD, SEM, EDX, and ICP-AES analysis.