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Carbon dioxide (CO2) is the product of burning fossil fuels and the most common greenhouse gas, which can be converted back into useful fuels in a sustainable manner. One promising way to convert CO2 emissions into fuel feedstock is a process called electrochemical reduction. But to be commercially viable, the process needs to be improved to select or produce more desired carbon-rich products. Now, as reported in the journal Nature Energy, Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a new method to improve the surface of the copper catalyst used for the auxiliary reaction, thereby increasing the selectivity of the process.
“Although we know that copper is the best catalyst for this reaction, it does not provide high selectivity for the desired product,” said Alexis, a senior scientist in the Department of Chemical Sciences at Berkeley Lab and a professor of chemical engineering at the University of California, Berkeley. Spell said. “Our team found that you can use the local environment of the catalyst to do various tricks to provide this kind of selectivity.”
In previous studies, researchers have established precise conditions to provide the best electrical and chemical environment for creating carbon-rich products with commercial value. But these conditions are contrary to the conditions that naturally occur in typical fuel cells using water-based conductive materials.
In order to determine the design that can be used in the fuel cell water environment, as part of the Energy Innovation Center project of the Ministry of Energy’s Liquid Sunshine Alliance, Bell and his team turned to a thin layer of ionomer, which allows certain charged molecules (ions) to pass through. Exclude other ions. Due to their highly selective chemical properties, they are particularly suitable for having a strong impact on the microenvironment.
Chanyeon Kim, a postdoctoral researcher in the Bell group and the first author of the paper, proposed to coat the surface of copper catalysts with two common ionomers, Nafion and Sustainion. The team hypothesized that doing so should change the environment near the catalyst—including the pH and the amount of water and carbon dioxide—in some way to direct the reaction to produce carbon-rich products that can be easily converted into useful chemicals. Products and liquid fuels.
The researchers applied a thin layer of each ionomer and a double layer of two ionomers to a copper film supported by a polymer material to form a film, which they could insert near one end of a hand-shaped electrochemical cell. When injecting carbon dioxide into the battery and applying voltage, they measured the total current flowing through the battery. Then they measured the gas and liquid collected in the adjacent reservoir during the reaction. For the two-layer case, they found that carbon-rich products accounted for 80% of the energy consumed by the reaction—higher than 60% in the uncoated case.
“This sandwich coating provides the best of both worlds: high product selectivity and high activity,” Bell said. The double-layer surface is not only good for carbon-rich products, but also generates a strong current at the same time, indicating an increase in activity.
The researchers concluded that the improved response was the result of the high CO2 concentration accumulated in the coating directly on top of the copper. In addition, negatively charged molecules that accumulate in the region between the two ionomers will produce lower local acidity. This combination offsets the concentration trade-offs that tend to occur in the absence of ionomer films.
In order to further improve the efficiency of the reaction, the researchers turned to a previously proven technology that does not require an ionomer film as another method to increase CO2 and pH: pulsed voltage. By applying pulsed voltage to the double-layer ionomer coating, the researchers achieved a 250% increase in carbon-rich products compared to uncoated copper and static voltage.
Although some researchers focus their work on the development of new catalysts, the discovery of the catalyst does not take into account operating conditions. Controlling the environment on the catalyst surface is a new and different method.
“We did not come up with a completely new catalyst, but used our understanding of reaction kinetics and used this knowledge to guide us in thinking about how to change the environment of the catalyst site,” said Adam Weber, a senior engineer. Scientists in the field of energy technology at Berkeley Laboratories and co-author of papers.
The next step is to expand the production of coated catalysts. The Berkeley Lab team’s preliminary experiments involved small flat model systems, which were much simpler than the large-area porous structures required for commercial applications. “It is not difficult to apply a coating on a flat surface. But commercial methods may involve coating tiny copper balls,” Bell said. Adding a second layer of coating becomes challenging. One possibility is to mix and deposit the two coatings together in a solvent, and hope that they separate when the solvent evaporates. What if they don’t? Bell concluded: “We just need to be smarter.” Refer to Kim C, Bui JC, Luo X and others. Customized catalyst microenvironment for electro-reduction of CO2 to multi-carbon products using double-layer ionomer coating on copper. Nat Energy. 2021;6(11):1026-1034. doi:10.1038/s41560-021-00920-8
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Post time: Nov-22-2021