New e-fuel technologies often use the reverse water gas shift reaction (RWGS) to convert atmospheric CO2 Although this reaction is efficient, it requires high temperatures and complex gas separation for high performance. For the first time in the world, scientists from Japan have now demonstrated record-high CO2 Conversion rates at relatively low temperatures in a modified chemical loop version of RWGS using a novel copper-indium oxide.
In the face of ever worsening climate change, there is a growing need for technologies that can capture and use atmospheric CO2 (Carbon dioxide) and reduce our carbon footprint. In the field of renewable energies, CO2E-fuels based on e-fuels have proven to be a promising technology that tries to convert atmospheric CO2 in clean fuels. The process involves the production of synthetic gas or synthesis gas (a mixture of hydrogen and carbon monoxide (CO)). With the help of the reverse water gas shift reaction (RWGS), CO2 is broken down into the CO required for synthesis gas. The RWGS reaction, while showing promise in its conversion efficiency, requires incredibly high temperatures (> 700 ° C) to proceed and produces undesirable by-products at the same time.
To address these issues, the scientists developed a modified version of the RWGS reaction that converts CO2 in a two-stage process to CO. First, a metal oxide used as an oxygen storage material is reduced by hydrogen. It is then reoxidized by CO2This process is free of undesirable by-products, simplifies gas separation and, depending on the oxide chosen, can be carried out at lower temperatures. As a result, scientists have sought oxide materials that have high rates of oxidation-reduction without requiring high temperatures.
In a recently published study in Chemical scienceScientists from Waseda University and ENEOS Corporation in Japan have found that a new type of indium oxide is modified with copper (Cu-In)2Ö3) has a record-breaking CO2 Conversion rate of 10 mmolh-1G-1 at relatively modest temperatures (400-500 ° C), making it a pioneer among the oxygen storage materials required for low temperature CO2 Conversion. To better understand this behavior, the team studied the structural properties of Cu-In oxide as well as the kinetics involved in the RWGS chemical loop reaction.
The scientists performed X-ray-based analyzes and found that the sample originally contained a starting material, Cu2In2Ö5, which was first reduced by hydrogen to form a Cu-In alloy and indium oxide (In2Ö3) and then oxidized by CO2 Cu – In to surrender2Ö3 and Co. X-ray data also showed that it was oxidized and reduced during the reaction, which gave the scientists the crucial clue. "The X-ray measurements made it clear that the chemically looped RWGS reaction is based on the reduction and oxidation of indium, which leads to the formation and oxidation of the Cu-In alloy," explains Professor Yasushi Sekine from Waseda University, who carried out the study.
The kinetic studies provided further insight into the reaction. The reduction step showed that Cu was responsible for the reduction of indium oxide at low temperatures, while the oxidation step showed that the Cu-In alloy surface maintained a highly reduced state while its bulk was oxidized. This allowed the oxidation to occur twice as fast as with other oxides. The team attributed this particular oxidation behavior to a rapid migration of negatively charged oxygen ions from the Cu-In alloy surface to their mass, which supported the preferred mass oxidation.
As expected, the results have excited scientists about the future prospects of copper indium oxides. "Given the current situation of carbon emission and global warming, a high-performance carbon dioxide conversion process is very desirable. While the chemically looped RWGS reaction works well with many oxide materials, our novel Cu-In oxide shows a remarkably higher performance here. We hope this will do significantly will help reduce our carbon footprint and lead humanity towards a more sustainable future, "concludes Sekine.