On-Orbit Processing and Hardware Performance of Microgravity Hydrothermal Synthesis for Graphene Aerogel

This study reports on the hydrothermal synthesis of graphene hydrogels (GHs) under microgravity on the International Space Station (ISS), using a custom-designed autoclave compatible with NASA's Solidification Using a Baffle in Sealed Ampoules (SUBSA) furnace. Extensive long-term stability tests of graphene oxide (GO) dispersion and GHs in deionized (DI) water were performed to verify their compatibility with the custom-designed autoclaves before launching to the ISS. Eight ampoules (2 autoclaves each, totaling 16 samples) filled with GO dispersion were launched to the ISS and heated to trigger the gelation reaction to synthesize GHs. The effectiveness of the designed leak-before-burst (LBB) safety technology for controlling the pressure inside the autoclave under safety requirements was demonstrated during the heating process on the ISS through the release of water vapor. For comparison, another eight ampoules filled with the GO dispersion were heated at the same temperature on Earth, resulting in 16 total control samples to analyze the effects of microgravity on the multiphysical properties of graphene aerogels (GAs). Both sets of GH samples prepared on the ISS and on Earth were transformed into GAs via solvent exchange to ethanol at ambient conditions, followed by critical point drying using carbon dioxide. Raman spectroscopy and scanning electron microscope (SEM) confirmed the successful synthesis of GAs on the ISS. As a continuation of the work, further characterization experiments are underway to comprehensively analyze the multiphysical properties of the graphene aerogels upon synthesis under microgravity conditions.