Efficient artificial photosynthesis systems follow the concept of the Z-scheme of natural photosynthesis. They are realized as catalyst- and surface-functionalized photovoltaic tandem devices [1,2] enabling photoelectrochemical water oxidation while simultaneously recycling CO₂ and generating hydrogen as a solar fuel for storable renewable energy. 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.

We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in microgravity environment, providing an alternative route to existing life support technologies for space travel [3]. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15mAcm^-2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the electrocatalyst using shadow nanosphere lithography [4]. We show that shadow nanosphere lithography can be used as a prosperous tool to obtain desired catalyst nanostructures of high fidelity on a light-absorbing semiconductor surface with tunable optical properties showing significant advantages for photoelectrochemical hydrogen production in microgravity and terrestrial applications [5].

References

[1] Young J. L., Steiner M. A., Döscher H., France R. M., Turner J. A., Deutsch T. G. (2017). “Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures”, Nat. Energ. 2. (17028).

[2] 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 19% Direct Water Splitting”, ACS Energy Lett. 3, 8, 1795-1800.

[3] Brinkert K., Richter M. H., Akay Ö., Liedtke J., Gierisig M., Fountaine K. T., Lewerenz H. J. (2018). Efficient Solar Hydrogen Production in Microgravity Environment. Nat. Commun. 9 (2527).

[4] Patoka P., Giersig M. (2011). “Self-assembly of latex particles for the creation of nanostructures with tunable plasmonic properties”, J. Mater. Chem. 21, 16783-16796.

[5] Brinkert K., Richter M. H., Akay Ö., Giersig M., Fountaine K. T., Lewerenz H.-J. (2018). “Advancing semiconductor-electrocatalyst systems: application of surface transformation films and nanosphere lithography”, Faraday Discuss. 208, 523-535.