Researchers from Zurich's Departments of Complex Materials and Renewable Energy Sources have succeeded in producing a solar reactor core from individually 3D printed ceramics. Solar reactors are used to produce carbon-neutral liquid fuels such as solar kerosene for the space industry. Therefore, the technology has great potential for lower emission aviation, which is possible through the use of additive manufacturing. Environmentally friendly fuels of this type can now be produced in larger quantities thanks to the increased efficiency of solar reactors. The project at ETH Zurich is made possible with funding from the Swiss Federal Office of Energy.

In short, a solar reactor functions by first being illuminated by sunlight from a parabolic mirror. The new reactor structure includes a 3D printed complex of hierarchically arranged ceramic structures. It opens on the surface facing the sun and tapers further towards the back of the reactor, trapping the heat. As the first successful tests at ETH Zurich showed, the whole structure is able to reach a reaction temperature of 1500°C due to the concentrated solar radiation. In addition, solar radiation is transported more efficiently inside the reactor thanks to the 3D printed components. As a result, twice as much carbon-neutral solar fuel is produced with the same amount of solar radiation compared to previous isotropic structures. The ceramic structures themselves are printed by extruding a specially developed paste from the 3D printer. The extruded paste consists of a large amount of cerium oxide particles to produce the most reactive material possible and thus maximize the efficiency of the solar reactor.

3D printed ceramic structure (left) and solar reactor (right)

ETH Zurich has been researching solar fuels for more than a decade and previously demonstrated their production process on the university campus in 2019. Engineers at the Swiss university have also already developed a solar reactor that uses the energy from concentrated solar radiation to produce synthesis gas (hydrogen and carbon monoxide) through a series of thermochemical cycles to separate water and CO2. This in turn is used to produce liquid solar fuels such as solar kerosene as jet fuel. These fuels are CO2 neutral because during their combustion only as much carbon is released as was previously extracted from the air to produce the synthesis gas. The structures previously used in the reactor had isotropic porosity. The sun's rays striking the reactor were attenuated on their way into the reactor due to the properties of the surface. This means that the optimum internal temperature cannot be reached in the reactor, limiting its performance and fuel production.

According to ETH Zurich, their newly developed technology is already very advanced, which is why ETH's separate companies, Climeworks and Synhelion, are looking to further develop the technology commercially, bring it to market, and collaborate with companies such as Zurich Airport and Lufthansa. In addition, the technology for 3D printing of ceramic structures has already been patented. Synhelion has also already received a license from ETH Zurich. Steinfeld, professor in the Department of Mechanical and Process Engineering at ETH Zurich, emphasizes: “ This technology has the potential to increase the energy efficiency of the solar reactor and thereby significantly improve the economic viability of sustainable aviation fuels ". 

Illustration of the 3D-printed reactor


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