Producing Oxygen and Other Chemicals via Artificial
Photosynthesis for Space Exploration
For us on Earth it is very normal that we do not think about where oxygen comes from: plants and cyanobacteria produce it for us for about 2.3 billion years. In less than one second, natural photosynthesis magically oxidises water with the help of sunlight and uses the produced protons and electrons in the so-called ‘dark reaction’ to reduce carbon dioxide to sugars. Oxygen is hereby only a ‘waste product’. It’s just so fantastic that we have nature!
It is easy to imagine that we need to solve a key problem for all space travels to the International Space Station (ISS), Mars or Moon: how do we produce sustainably and efficiently oxygen (and an artificial atmosphere) for long periods of time? How do we recycle carbon dioxide exhaled by astronauts?
Currently, oxygen and hydrogen are produced through water electrolysis in the so-called “oxygen generator assembly” (OGA) on the ISS. The energy required for the reaction is fed into the reactor from incoming sunlight via solar panels outside the space station. That sounds great - it sounds like everything works already! Not quite. The near-absence of buoyancy caused by microgravitation on the ISS hinders the detachment of gas bubbles from electrodes in the electrolyser and the produced gases (oxygen and hydrogen) can only be detached and utilised through rotation. This requires a lot of energy: 1.5 kW out of the 4.6 kW used by the entire Environmental Control and Life Support System (ECLSS) on the ISS is used by the OGA to produce oxygen for crew members.
Our research group works on the development of alternative methods to produce oxygen and other chemicals (such as hydrogen) efficiently and sustainably for long time periods at minimal energy input: our aim is to mimic the key processes of natural photosynthesis to design so-called “artificial photosynthesis devices”. Instead of chlorophyll, we utilise semiconductors to absorb light and coat them with electrocatalysts to integrate the processes of light absorption, charge separation and catalysis. This allows us to potentially produce oxygen and hydrogen using less weight and volume than traditional electrolysers. Semiconductors and electrocatalysts can moreover be energetically altered and optimised for a large variety of reactions: we not only work on the realisation of an autonomic oxygen and hydrogen production device in microgravity, but also on the (photo-)electrochemical reduction of carbon dioxide and the production of other chemicals such as urea (a fertiliser) and more complex precursors for pharmaceuticals.
Other research topics in our group include:
The development of alternative, passive phase separation systems for gas bubble detachment from electrode surfaces in microgravity (e.g., via electrocatalyst nanostructures or the utilization of magnetically-induced buoyancy).
The simulation of (photo-)electrochemical devices in microgravity using COMSOL Multiphysics, OpenFOAM and numerical methods, specifically focusing on simulating mass transfer in the electrolyte and gas bubble evolution.
The (photo-)electrodeposition of metals on (photo-)electrodes in microgravity and the investigation of the impact gravity has on the nucleation and growth of metal layers and the metal nanotopography.
Experiments in the Bremen Drop Tower
How can we produce oxygen, hydrogen and other chemicals in weightlessness? What do we need that for anyway and how can we benefit from it here on Earth?
Our projects are currently supported through the German Aerospace Center (DLR, LiMo #50WM2150 und SolarMag #50WM2358) and the European Space Agency (ESA, OISP Idea #I-2022-00037 und #I-2023-01969).