Emergent e-fuel technologies often use the reverse water-gas reaction (RWGS) to convert atmospheric CO2 CO. Although effective, this reaction requires high temperatures and complex gas separation for high performance. However, for the first time in the world, scientists from Japan have now shown record high CO2 conversion rates at relatively low temperatures in a modified version of RWGS with chemical loops using new copper-indium oxide.
With worsening climate change, there is a growing need for technologies that can capture and harness atmospheric CO2 (carbon dioxide) and reduce our carbon footprint. In the field of renewable energy CO2E-based fuels have emerged as a promising technology trying to convert atmospheric CO2 in pure fuels. The process involves the production of synthetic gas or synthetic gas (a mixture of hydrogen and carbon monoxide (CO)). With the help of the reverse displacement of water and gas (RWGS), CO2 it decomposes to the CO required for synthetic gas. Although it promises its conversion efficiency, the RWGS reaction requires incredibly high temperatures (> 700 ° C) and at the same time generates unwanted by-products.
To solve these problems, scientists have developed a modified version of the RWGS reaction with chemical loops that converts CO2 on the CO method in two steps. First, hydrogen is reduced to a metal oxide, which is used as an oxygen storage material. CO is then re-oxidized2, thus obtaining CO. This method is free of unwanted by-products, simplifies gas separation and can be made feasible at lower temperatures, depending on the oxide selected. Consequently, scientists have been looking for oxide materials that show high rates of oxidation reduction without the need for high temperatures.
In a recent study published in Chemical science, scientists from Waseda University and ENEOS Corporation in Japan have discovered that the new Indian oxide has been modified with copper (Cu – In2ON3) exhibits record CO2 conversion rate of 10 mmolh-1Mr-1 at relatively modest temperatures (400-500 ° C), making it a leader among the oxygen storage materials needed for CO at low temperatures2 conversion. To better understand this behavior, the team investigated the structural properties of Cu-In oxide along with the kinetics involved in the chemical loop of the RWGS reaction.
The scientists performed X-ray analyzes and found that the sample initially contained the parent material Cu2In2ON5, which was first reduced with hydrogen to form Cu-In alloys and indium oxide (In2ON3) and then oxidizes CO2 to obtain Cu – In2ON3 and CO. X-ray data further revealed that it underwent oxidation and reduction during the reaction, providing a key clue to scientists. “X-ray measurements have clearly shown that the chemically looped RWGS reaction is based on the reduction and oxidation of indium leading to the formation and oxidation of Cu-In alloys,” explains Professor Yasushi Sekine of Waseda University, who led the study.
Kinetic tests provided further insight into the reaction. The reduction step revealed that Cu was responsible for the reduction of Indian oxide at low temperatures, while the oxidation state showed that the surface of the Cu-In alloy maintained a highly reduced state while most of it was oxidized. This allowed oxidation to occur twice as fast as that of the oxide. The team attributed this unusual oxidative behavior to the rapid migration of negatively charged oxygen ions from the surface of the Cu-In alloy to its bulk, which aided in preferential oxidation.
The results, quite unexpectedly, excited scientists about the future prospects of copper-Indian oxides. “Given the current situation with carbon emissions and global warming, a high-performance carbon dioxide conversion process is highly desirable. Although the chemically looped RWGS reaction works well with many oxide materials, our new Cu-In-oxide here shows extremely higher performance than any from them. We hope that this will significantly contribute to reducing our carbon footprint and guiding humanity towards a more sustainable future, “Sekine concludes.
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