Magnetically-Induced Buoyancy for Efficient Electrochemical Oxygen Production in Microgravity

Abstract

The realization of long-term space travels and the establishment of a lunar research platform are challenged by the lack of technological device architectures for efficient, stable and continuous oxygen production. One obstacle is that the near-absence of buoyancy in microgravity results in hindered gas bubble desorption at the electrode-electrolyte interface, causing lower efficiencies for electrolyser systems when operating in space.1,2 The significantly reduced buoyancy force also has severe complications for phase separation, which is a crucial process for a variety of space technologies also including heat transfer, fuel production and removal of carbon dioxide from cabin air. Multiple approaches have been studied in the past to induce phase separation such as creating centrifugal force fields. These approaches lack however efficiency, stability and robustness.3,4 In our recent work, we demonstrate the use of magnetic polarisation to artificially induce buoyancy in the electrolytic oxygen evolution half-cell reaction and thus significantly increasing the overall half-cell efficiency. This was carried out in a series of experiments at the Bremen Drop Tower, Center of Space Technology and Microgravity (ZARM, Germany), where short-term microgravity conditions of 9.2 s were achieved.5,6. Chronoamperometric and cyclic voltammetry measurements on high-activity RuOx electrocatalyst structures on a Ti substrate were undertaken with and without a magnet in close proximity to the electrode to closely monitor the electrochemical performance in a three-electrode potentiostatic arrangement and to demonstrate the magnetic effect on gas bubble desorption during free fall. It was observed that current densities for the electrodes at a potential of +1.49 V vs RHE were significantly higher in the presence of a magnet. We conclude that magnetic phase separation can be utilised in electrolytic systems in reduced gravitational environments to efficiently detach oxygen bubbles from the electrode surface and operate the devices at higher efficiencies, providing a key advancement for future oxygen production in space missions.2,3,5 References Cheng, W.-H.; Richter, M. H.; May, M. M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H. A.; Lewerenz, H.-J. (2018). Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Lett., 3, 1795−1800.Saravanabavan, S.; Coulthard, C. T.; Kaur, M.; Brinkert, K. (2022). Catalysis in Space Environments. doi.org/10.1002/9783527830909.ch7 In: Hessel V., Stoudemire J., H. Miyamoto & I. D. Fisk (Eds.). In Space Manufacturing and Resources.Wiley-VCH. ISBN: 978-3-527-83091-6Romero-Calvo, Á.; Akay, Ö.; Schaub, H.; Brinkert, K. (2022). Magnetic phase separation in microgravity. npj Microgravity 8 (32). doi.org/10.1038/s41526-022-00212-9.Harvey, A.; Ramshaw, C.; Reay, D. A. Process Intensification: Engineering for Efficiency. Sustainability and Flexibility. 2nd edition. Butterworth- Heinemann; 201Brinkert, K.; Richter, M. H.; Akay, Ö.; Liedtke, J.; Giersig, M.; Fountaine, K. T.; Lewerenz, H. J. (2018). Efficient solar hydrogen production in microgravity environment. Commun. 9(2527). doi: 10.1038/s41467-018-04844-yhttps://www.zarm.uni-bremen.de/fileadmin/user_upload/drop_tower/Users_Manual_0412.pdf