How exactly does photoelectrocatalysis work?

Photoelectrocatalysis is a process that mimics natural photosynthesis. It combines elements of photochemistry, photophysics, and electrocatalysis. Essentially, we use semiconductors, such as those used in computer screens, as artificial light absorbers, similar to the way plants use chlorophyll. These semiconductors are equipped with electrocatalysts that can catalyze certain reactions. Depending on the type of charge that is released by the light absorption and transferred to the electrocatalyst (electrons or holes), reduction or oxidation reactions can be carried out. For example, we can produce hydrogen when protons are reduced, while oxygen is produced when water is oxidized.

In other words, you are investigating how artificial photosynthesis can work on other planets.

Exactly. We are deepening our understanding of artificial photosynthesis by mimicking the principles of natural photosynthesis. This approach is known as biomimetics. Our research focuses on mimicking and understanding the exact processes in the plant that are important for the production of oxygen and other energy-rich compounds such as hydrogen. Our long-term goal is to produce these elements in space with the help of sunlight.

And why did you not use natural photosynthesis for this?

The decision to use artificial photosynthesis was based on the need to develop adaptable technologies for use in space. We do have solar energy there, as well as CO2 and, if we provide it, water. These resources are available both on Mars and on the Moon. However, the task of carrying out photosynthesis on these planets much more challenging than on Earth. Photosynthesis is a biological process in which plants, algae, and some bacteria use light energy to transform carbon dioxide and water into glucose and oxygen. This process is closely linked to the specific environmental conditions on Earth. There are several reasons, such as gravity, atmosphere, and temperature, why photosynthesis would not necessarily work the same way on other planets. In addition, the light spectrum plays a role, as plants on Earth are adapted to the specific spectral lengths of sunlight. On Moon and Mars, the sunlight spectrum is different, which influences the effectiveness of photosynthesis. Besides, natural photosynthesis produces starch as an energy source, but this does not meet our energy requirements in society.

Why is the production of oxygen and other chemical compounds vital for space missions?

Space missions need to be self-sufficient in an extreme environment. The production of oxygen and other compounds plays a crucial role as they form the basis for the life support systems of spacecraft and stations. A practical example is the continuous supply of breathable air, which is ensured by oxygen production. Without this self-sufficient supply, a long-term mission in space would not be possible. For space missions, sustainable methods of oxygen production and CO2 recycling are crucial. Although astronauts on the ISS already have functioning oxygen production systems, they produce oxygen by electrolysis of water, which is powered by external solar cells and requires large amounts of energy. Our research seeks to develop alternative methods to make these processes more efficient and sustainable in microgravity. Self-sufficiency in terms of vital resources such as oxygen and hydrogen is essential for long-term missions and the exploration of space. Therefore, the production of oxygen and other chemical compounds is not only a technological challenge, but also a fundamental requirement for survival and the success of future space missions.

How can a system that relies on sunlight function efficiently in the extreme Martian winter, where the amount of sunlight is significantly lower than on Earth? The challenge seems to be particularly daunting at this time of year, when the sun is not available for long periods.

This is obviously an important point, as efficient energy storage mechanisms must be considered for systems that rely on solar energy. Incidentally, the storage mechanisms are not only relevant for the Martian winter, but play a role all year round. On Mars, they have to store far more energy than on the Moon or Earth, as solar radiation is generally much lower here.

To what extent could the technology you are developing for space missions help to use energy more efficiently not only on Mars, but also here on Earth?

Our research into artificial photosynthesis and photoelectrocatalysis has the potential to be applied not only to space technology, but also to drive advances in energy efficiency and the green energy transition here on Earth. The key lies in the efficient, direct use of solar energy, especially for the production of fuels such as hydrogen. This is important especially as the demand for green fuels grows. As green fuels in turn rely on renewable energy sources, the results of our research could help to improve the efficiency of solar energy conversion and storage. As a result, this technology would not only benefit space missions, but also drive the development of environmentally friendly energy systems and the reduction of CO2 emissions on our planet.

Looking to the future, how do you see the role of photoelectrocatalysis in our daily lives, whether on Earth or for future space missions?

Looking into the future remains speculative, of course, as we are still working on increasing the stability of our system for better performance. In order to optimize it further, we are also working with models, which help to predict the efficiencies on Moon and Mars. Another aspect we need to consider when looking ahead is the question of funding for systems powered directly by sunlight. Here, better technological and economic modeling can help to find cheaper and more sustainable materials, for example. In general, there are many interesting avenues for catalytic foundation research, as we are also investigating how gravity and low temperatures affect the electrochemical production of chemical compounds.

At the same time, we believe that there might be a number of useful applications. For example, use in desert and/or polar regions would be an option, where we could produce fertilizers locally with the help of sunlight using nitrogen from the air without any existing infrastructure. In polar regions, the climatic conditions could allow us to efficiently extract CO2 from the atmosphere to generate fuels locally.

About Katharina Brinkert and the Humans on Mars Initiative

The Humans on Mars Initiative investigates innovative solutions for sustainable human exploration of Mars. The great potential benefits for Earth are demonstrated by research of the Photoelectrocatalysis working group headed by Katharina Brinkert. It is looking into the production of oxygen and other chemicals through artificial photosynthesis. To this end, experiments are being carried out in microgravity in the Drop Tower of the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen.