Towards sustaining efficient (photo)electrolysis in microgravity: nanotopographical and magnetic field explorations

Long-duration space missions beyond Earth orbit necessitate advanced resource management systems, wherein photoelectrochemical water splitting offers a multifunctional solution for direct solar-to-chemical energy conversion, enabling both oxygen generation for life support and energy storage via hydrogen production. This dissertation examines these fundamental (photo)electrochemical processes under microgravity condition, addressing how absence of buoyancy alters gas-liquid phase separation dynamics and consequent solar energy conversion efficiency at semiconductor/electrocatalyst interfaces. Using the Bremen Drop Tower’s 9.2 second microgravity period, systematic investigations of hydrogen evolution reaction at photocatalytic interfaces were conducted, comparing nanostructured electrocatalysts fabricated via shadow nanosphere lithography with conventional thin-film coatings. The results demonstrate that nanostructured rhodium-coated p-type doped indium phosphide photocathodes maintain consistent solar-to-hydrogen conversion e!ciency during the microgravity period, whereas thin-fillm catalyst layers experience significant photocurrent reduction, whereby a critical trade-of between wettability properties and photocurrent performance was observed across different nanostructuring parameters. Hydrogen bubble growth follows sigmoidal patterns with structure-dependent logistic function parameters, indicating mechanistic differences in gas evolution kinetics. Furthermore, complete water splitting under microgravity conditions was successfully demonstrated, whereby magnetohydrodynamic propulsion systems in proton-exchange membrane electrolysers enable substantial performance enhancements (up to 139.8% for platinum mesh electrodes) by replacing buoyancy-driven convection. These findings establish fundamental design principles for space-optimised solar water electrolysis technologies, facilitating the development of robust solar-powered life support and energy storage systems for future space missions.