ETH Zurich researchers achieve more efficient production of solar fuels

In Switzerland, in recent years, engineers at ETH Zurich have developed the technology to produce liquid fuels from sunlight and air. In 2019, they demonstrated the entire thermochemical process chain under real conditions for the first time, in the middle of Zurich, on the roof of ETH Machine Laboratory. These synthetic solar fuels are carbon neutral because they release only as much CO2 during their combustion as was drawn from the air for their production. Two ETH spin- offs, Climeworks and Synhelion, are further developing and commercializing the technologies.

At the heart of the production process is a solar reactor that is exposed to concentrated sunlight delivered by a parabolic mirror and reaches temperatures of up to 1500 degrees Celsius. Inside this reactor, which contains a porous ceramic structure made of cerium oxide, a thermochemical cycle takes place for splitting water and CO2 captured previously from the air. The product is syngas: a mixture of hydrogen and carbon monoxide, which can be further processed into liquid hydrocarbon fuels such as kerosene (jet fuel) for powering aviation.

Until now, structures with isotropic porosity have been applied, but these have the drawback that they exponentially attenuate the incident solar radiation as it travels into the reactor. This results in lower inner temperatures, limiting the fuel yield of the solar reactor.