University of Cambridge researchers have used perovskites to develop a solar-powered technology that converts carbon dioxide and water into liquid fuels that can be added directly to a car’s engine as drop-in fuel.
The researchers relied on photosynthesis to convert CO2, water and sunlight into multicarbon fuels – ethanol and propanol – in a single step. These fuels have a high energy density and can be easily stored or transported.
It was said that unlike fossil fuels, these solar fuels produce net zero carbon emissions and are completely renewable, and unlike most bioethanol, they do not divert any agricultural land away from food production. While the technology is still at laboratory scale, the researchers say their ‘artificial leaves’ are an important step in the transition away from a fossil fuel-based economy.
For several years, the research group has been developing sustainable, zero-carbon fuels inspired by photosynthesis – the process by which plants convert sunlight into food – using artificial leaves. To date, these artificial leaves have only been able to make simple chemicals, such as syngas, a mixture of hydrogen and carbon monoxide that is used to produce fuels, pharmaceuticals, plastics and fertilizers. But to make the technology more practical, it would need to be able to produce more complex chemicals directly in a single solar-powered step. Now, the artificial leaf can directly produce clean ethanol and propanol without the need for the intermediary step of producing syngas.
The scientists assembled the artificial leaf devices by integrating an oxide-derived Cu94Pd6 electrocatalyst with perovskite–BiVO4 tandem light absorbers that couple CO2 reduction with water oxidation. The wired Cu94Pd6|perovskite–BiVO4 tandem device provides a Faradaic efficiency of ~7.5% for multi-carbon alcohols (~1:1 ethanol and n-propanol), whereas the wireless standalone device produces ~1 µmol cm−2 alcohols after 20 h unassisted operation under air mass 1.5 G irradiation with a rate of ~40 µmol h−1 gCu94Pd6−1.
This study demonstrates the direct production of multi-carbon liquid fuels from CO2 over an artificial leaf and, therefore, brings us a step closer to using sunlight to generate value-added complex products. Other scientists have been able to produce similar chemicals using electrical power, but this is the first time that such complex chemicals have been produced with an artificial leaf using only the energy from the Sun.
“Shining sunlight on the artificial leaves and getting liquid fuel from carbon dioxide and water is an amazing bit of chemistry,” said Dr. Motiar Rahaman, the paper’s first author. “Normally, when you try to convert CO2 into another chemical product using an artificial leaf device, you almost always get carbon monoxide or syngas, but here, we’ve been able to produce a practical liquid fuel just using the power of the Sun. It’s an exciting advance that opens up whole new avenues in our work.”
At present, the device is a proof of concept and shows only modest efficiency. The researchers are working to optimize the light absorbers so that they can better absorb sunlight and optimising the catalyst so it can convert more sunlight into fuel. Further work will also be required to make the device scalable so that it can produce large volumes of fuel.