Faster, Cooler Ways to Reduce Our Carbon Base: Copper-Indium Oxide

The chemical-looping version of the reverse water-gas shift reaction (RWGS-CL) can help convert CO2 to CO at lower temperatures while there are no pleasant side effects, allowing simple gas separation. Credit: Yasushi Sekine from Waseda University

Scientists set a record for the highest conversion rate of carbon dioxide at low temperatures with copper-modified indium oxide, signaling sustainable e-fuel.

With the ever-changing climate, there is a need for technology that can capture and use atmospheric CO2 (carbon dioxide) and reduce our carbon footprint. In the realm of renewable energy, CO2-basic e-fuels emerge as promising technologies that attempt to change atmospheric CO2 to clean fuel. The process involves the production of synthetic gas or syngas (a mixture of hydrogen and carbon monoxide (CO)). With the help of a reverse water-gas (RWGS) reaction, CO2 broken down into CO required for syngas. While promising in its conversion efficiency, the RWGS reaction requires a very high temperature (> 700 ° C) to continue, while also producing unwanted by-products.

To address this issue, scientists are developing a chemical-looping version of the RWGS reaction that alters CO2 to CO in a two-step method. First, metal oxides, used as oxygen storage materials, are reduced by hydrogen. Then, it is oxidized again by CO2, produce CO. This method is free from unpleasant side effects, makes gas separation easier, and can be done at lower temperatures depending on the oxide selected. As a result, scientists have been looking for oxides that indicate high levels of oxidation reduction without the need for high temperatures.

In a new study published in Chezed Science, scientists from Waseda University and ENEOS Corporation in Japan have revealed that the novel indium oxide is modified by copper (Cu-In2O3) indicates the CO that breaks the record2 10 mmolh conversion rate-1g-1 at relatively moderate temperatures (400-500 ° C), making it the raw material among the oxygen storage materials required for low CO temperatures2 conversion. To better understand this behavior, the team studied the structural properties of Cu-In oxide together with the kinetics involved in the chemical RWGS-loop reaction.

Cooler Ways to Reduce Our Carbon Impressions

High levels of CO2 conversion at relatively low temperatures in the chemical-looping version of the RWGS using the novel copper-indium oxide. Credit: Waseda University

Scientists performed an X-ray analysis and found that the first sample contained the mother material, Cu2in2O5, which was first reduced by hydrogen to form Cu-In alloy and indium oxide (Dina2O3) then oxidized by CO2 produce Cu-In2O3 and CO-X-ray data further reveal that it undergoes oxidation and reduction during reaction, providing key clues for scientists. “X-ray measurements clearly indicate that the chemically reversed RWGS reaction is based on the reduction and oxidation of Indium that leads to the formation and oxidation of Cu-In alloys,” explains Professor Yasushi Sekine from Waseda University, who led the study.

Kinetic research provides more on the reaction. The reduction step reveals that Cu is responsible for the reduction of indium oxide at lower temperatures, while the oxidation step indicates that the surface of the Cu-In alloy preserves reduced conditions when its volume is oxidized. This allows oxidation to occur twice as fast as other oxides. The team demonstrated this typical oxidation behavior for the rapid migration of negatively charged oxygen ions from the surface of Cu-In alloys to large quantities, which aids in mass oxidation.

As a result, rather expected, scientists are excited about the future prospects of copper-indium oxide. “Due to the current state of carbon emissions and global warming, the process of converting high performance carbon dioxide is highly desirable. Although the chemically reversed RWGS reaction works very well with oxide materials, our Cu-In-oxide novel here demonstrates higher performance than “We hope this will contribute significantly to reducing our carbon footprint and driving people towards a more sustainable future,” concluded Sekine.

References: “Rapid migration of oxygen ions in many Cu – In – oxides and their use for effective CO2 conversion at low temperatures ”by Jun-Ichiro Makiura, Takuma Higo, Yutaro Kurosawa, Murakami City, Shuhei Ogo, Hideaki Tsuneki, Yasushi Hashimoto, Yasushi Satob and Yasushi Sekine, December 23, 2020, Chemistry.
DOI: 10.1039 / d0sc05340f

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