Artificial photosynthesis is possible

mobility Refuel carefree thanks to artificial photosynthesis

A tempting vision. Humans solve their energy problem by doing what nature dictates: Generating hydrogen with the energy of the sun. Physicist Thomas Hannappel from the Technical University in Ilmenau is currently researching how this can work together with his colleagues. If it succeeds, there are many advantages for him:

Then you have energy that can be stored and used anywhere, and that also meets mobility requirements. The original fuel, which nature has produced itself for many millions, even billions of years, is hydrogen.

Prof. Thomas HannappelTU Ilmenau

In the eyes of scientists, this is the material that makes the energy transition possible in the first place. Because there are infinite quantities of it. We just need to catch it, convert it into energy in fuel cells and use it to drive a motor. From the train, the bus, the car, or even from the combined heat and power unit that is down in the basement and heats the house. Together with researchers from the USA and the Helmholtz Center in Berlin, Thomas Hannappel wants to directly imitate a process from nature: photosynthesis.

Water is split in the leaves of the plants. The water comes from the earth, goes into the leaves, and that's where photosynthesis takes place.

Prof. Thomas Hannappel

The secret lies in the artificial leaf

Instead of a natural tree leaf, the researchers use semiconductor surfaces. There are still a few refinements to it, but the core element is semiconductors. Conventional solar cells also consist of semiconductors. However, it is the energy that wins, not the hydrogen. The cells for artificial photosynthesis, on the other hand, do. They are wafer-thin, thinner than a leaf.

The artificial leaf doesn't need a single power cord. You just have to put it in the water, then light has to fall on it and it generates hydrogen and oxygen. So it can be used anywhere.

Prof. Thomas Hannappel

The energy, i.e. the light for photosynthesis, is captured with tandem solar cells that the scientists have built into the artificial leaf. This allows them to capture a wider spectrum of sunlight and gain more energy for the process. Another challenge was the different materials that make photosynthesis possible. After all, they have to lie in the water for many years without corroding. Electrochemist Prof. Andreas Bund gives a little insight:

It's a walk through the whole periodic table. Titanium dioxide, aluminum, indium, phosphite, gallium, arsenite and ruthenium oxide. These are materials that are sometimes expensive, but very effective for this application.

Prof. Thomas BundTU Ilmenau

New efficiency record

Effective means that they only last 100 hours. Then some materials will start to rust around the edges. But 100 hours were still unthinkable a few years ago. The energy yield is also a great success. The Ilmenau company announces 19 percent efficiency. Nobody has managed that so far.

The development stagnated for practically 17 years. In 2014 we were able to increase efficiency for the first time to 14 percent and now even to 19 percent and that is certainly impressive.

Prof. Thomas Hannappel, physicist

For this calculation, the researchers assume an output power of 1000 watts per square meter. That is what the sun does on a normal sunny day. So the output is 190 watts. This makes researchers more efficient than nature.

But nature can allow itself a low efficiency, but it convinces with growth.

Prof. Thomas Hannappel

Artificial photosynthesis is considered to be one of the most demanding tasks in chemistry. In 1912 an Italian chemist first drew attention to their "civilizational advantages". Then the subject was off the table again. It wasn't until 60 years later that researchers dared to approach again. Since then, the efficiency has increased more and more, to 19 percent.

Politicians also see artificial photosynthesis as a possible factor in a successful turnaround in energy and raw materials. This emerges from the response of the federal government to a request from the FDP parliamentary group, which was published on February 28, 2019. However, there is still a long way to go before the market launch. At the moment, only the feasibility has been proven. A lot of innovation work has to be done before it can be used economically, especially in cooperation with industry. This so-called collaborative research is funded by the federal government. Artificial photosynthesis is a research focus for the Federal Ministry of Education and Research.

A hydrogen filling station at home in sight?

For Thomas Hannappel, hydrogen production in his own cellar is the logical consequence. Even if he admits that it can take around 10 years for the cells to mature accordingly. Then photosynthesis is definitely competitive for him, even when used as a domestic gas station.

When the sun is shining, pressure tanks would have to be filled with the hydrogen obtained. And if you need electricity, the hydrogen is converted into electricity in the fuel cell.

Prof. Thomas Hannappel

Artificial leaves as a CO2 eater

The physicists Matthias May (Helmholtz-Zentrum Berlin) and Kira Rehfeld (University of Heidelberg) also see artificial photosynthesis as an opportunity to relieve our earth's atmosphere of CO2. The advantage over reforestation, which also binds C02: It is faster and works even on smaller, less fertile areas.

May and Rehfeld calculated how much forest would have to be reforested in order to remove 10 gigatons of CO2 from the atmosphere every year. That much is necessary to offset the climate balance in a medium scenario. The result: It would have to be an area the size of Europe that would then no longer be available for agriculture.

An area the size of Brandenburg would be sufficient for artificial photosynthesis. That could even be in the desert, because the modules advised by May and Rehfeld would hardly need any water. The two researchers are not interested in the production of hydrogen, but rather in binding CO2 molecules and converting them into stable chemical compounds. These could then be further processed, react to form solid materials and even be used in the form of plastic as a building material. Even if all of this will be possible in a few years, Matthias May sees the key to solving the climate problem on the doorstep:

The best thing would be to drastically reduce CO2 emissions immediately, it would be safer and much cheaper.

Matthias MayHelmholtz Center Berlin