Electrochemical Interfacial Phenomena Under Microgravity

Electrochemical Processing under extreme conditions like reduced gravity, strong cosmic ray irradiation and magnetic fields should be well designed in the era of Gateway after ISS. JAXA’s “HAYABUSA” satellite project of Successful Sample Return from Asteroid “Itokawa” was achieved by newly developed Ion Engine and well controlled life-cycling of LIB. Now, HAYABUSA 2” is approaching to “Ryugu” asteroid by Pin-point Landing supported with Robotics & AI Image Learning (Self Controlled Driving). Moreover, Manned Rover operation plan toward Lunar Hydrogen Energy System in 2029 was announced by JAXA-TOYOTA last March. CO 2 Reduction for Life Supporting System must be reasonably combined. HERACLES (Human Enhanced Robotic Architecture for Lunar Exploration and Science) and MMX (Martian Moons eXploration) shall be further planned. High Temp. Molten Oxide Electrolysis with Inert Anode are engaged as ISRU. One of the fundamental subjects common in designing the energy conversion and storage devices in space engineering is to well control the electrochemical interfacial phenomena among three Gas/Liquid(Aqueous or Molten Oxide)/Solid(Metal or Solid Oxide) phases under reduced gravity and magnetic field. Experimental studies in Drop Tower, a parabolic flight and University Laboratory(1-G) to focus the wettability effects on these phenomena were reported over last 30 years 1-10) . O 2 bubble evolution behavior on Pt electrode modified by thiol SAM was monitored during alkaline water electrolysis under μ-G with a high speed video camera. Single bubble measurements on microwire electrode was additionally engaged. The latter revealed three-step processes involving (1) the nucleation and formation of supersaturated layer of dissolved O 2 gas followed by (2) a rapid growth depending on the gas diffusion process and finally (3)a stable growth where its growth rate is dominated by bubble configuration depending on the contact angle. Moreover, the correlation of multiple gas bubble observation with electrochemical data and surface coverage on the plate electrode reinforces the importance of wettability in determining two phase flow motion and energy consumption during electrolysis. The degree of supersaturation of dissolved gas on hydrophilic/hydrophobic electrode surface in aqueous solution and molten salt are also studies. They are compared to 1-G experiments in order to newly enlighten the matured gas electrode concepts. “Electrochemical Laboratory in ISS & Gateway” should be constructed with Space Agencies.