Artificial photosynthesis systems, which follow the concept of the Z-scheme of natural photosynthesis, are presently being realized as catalyst-functionalized photovoltaic tandem devices for the photoelectrochemical oxidation of water and the simultaneous generation of hydrogen as a so-called “solar fuel”. The successful implementation of an efficient photoelectrochemical (PEC) water splitting cell is not only a highly desirable approach to solving the energy challenge on earth: an effective air revitalization system generating a constant flux of O₂ while simultaneously recycling CO₂ and providing a sustainable fuel supply is also essential for the International Space Station and long-term space missions, where a regular resupply from earth is not possible.

Here, we present the photoelectrochemical production of hydrogen in microgravity environments on p-type indium phosphide electrodes with deposited rhodium electrocatalysts. Our findings indicate that microgravity has a significant impact on the gas bubble evolution behaviour and the mass transfer rate of the evolved hydrogen gas on the electrode surface. Furthermore, microgravity influences the current-voltage characteristics and the overall solar-to-hydrogen efficiency of the catalyst functionalized semiconductor-based half-cell. Further experiments with nanostructured rhodium catalysts fabricated by shadow nanosphere lithography on the InP surface suggest that the structure of the electrode surface plays a significant role for the gas bubble evolution behaviour and for the further the development of efficient prototypes for solar-assisted water splitting and hydrogen production that operate in micro- and hypergravity environments.