{"id":137733,"date":"2024-01-23T07:11:00","date_gmt":"2024-01-23T06:11:00","guid":{"rendered":"https:\/\/renewable-carbon.eu\/news\/?p=137733"},"modified":"2024-01-17T10:07:09","modified_gmt":"2024-01-17T09:07:09","slug":"catalytic-combo-converts-co2-to-solid-carbon-nanofibers","status":"publish","type":"post","link":"https:\/\/renewable-carbon.eu\/news\/catalytic-combo-converts-co2-to-solid-carbon-nanofibers\/","title":{"rendered":"Catalytic Combo Converts CO2\u00a0to Solid Carbon Nanofibers"},"content":{"rendered":"\n\n\n

Scientists at the U.S. Department of Energy\u2019s (DOE) Brookhaven National Laboratory and Columbia University have developed a way to convert carbon dioxide (CO2<\/sub>), a potent greenhouse gas, into carbon nanofibers, materials with a wide range of unique properties and many potential long-term uses. Their strategy uses tandem electrochemical and thermochemical reactions run at relatively low temperatures and ambient pressure. As the scientists describe in the journal Nature Catalysis<\/em>, this approach could successfully lock carbon away in a useful solid form to offset or even achieve negative carbon emissions.<\/strong><\/p>\n\n\n

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\"Nanofibers\"
Scientists have devised a strategy for converting carbon dioxide (CO2<\/sub>) from the atmosphere into valuable carbon nanofibers. The process uses tandem electrocatalytic (blue ring) and thermocatalytic (orange ring) reactions to convert the CO2<\/sub> (teal and silver molecules) plus water (purple and teal) into “fixed” carbon nanofibers (silver), producing hydrogen gas (H2<\/sub>, purple) as a beneficial byproduct. The carbon nanofibers could be used to strengthen building materials such as cement and lock away carbon for decades. \u00a9<\/strong> Zhenhua Xie\/Brookhaven National Laboratory and Columbia University; Erwei Huang\/Brookhaven National Laboratory<\/figcaption><\/figure><\/div>\n\n\n
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\u201cYou can put the carbon nanofibers into cement to strengthen the cement,\u201d said Jingguang Chen, a professor of chemical engineering at Columbia with a joint appointment at Brookhaven Lab who led the research. \u201cThat would lock the carbon away in concrete for at least 50 years, potentially longer. By then, the world should be shifted to primarily renewable energy sources that don\u2019t emit carbon.\u201d<\/p>\n<\/blockquote>\n\n\n\n

As a bonus, the process also produces hydrogen gas (H2<\/sub>), a promising alternative fuel that, when used, creates zero emissions.<\/p>\n\n\n\n

Capturing or converting carbon<\/h3>\n\n\n\n

The idea of capturing CO2<\/sub> or converting it to other materials to combat climate change is not new. But simply storing CO2<\/sub> gas can lead to leaks. And many CO2<\/sub>conversions produce carbon-based chemicals or fuels that are used right away, which releases CO2<\/sub> right back into the atmosphere.<\/p>\n\n\n\n

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\u201cThe novelty of this work is that we are trying to convert CO2<\/sub> into something that is value-added but in a solid, useful form,\u201d Chen said.<\/p>\n<\/blockquote>\n\n\n\n

Such solid carbon materials\u2014including carbon nanotubes and nanofibers with dimensions measuring billionths of a meter\u2014have many appealing properties, including strength and thermal and electrical conductivity. But it\u2019s no simple matter to extract carbon from carbon dioxide and get it to assemble into these fine-scale structures. One direct, heat-driven process requires temperatures in excess of 1,000 degrees Celsius.<\/p>\n\n\n\n

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\u201cIt\u2019s very unrealistic for large-scale CO2<\/sub> mitigation,\u201d Chen said. \u201cIn contrast, we found a process that can occur at about 400 degrees Celsius, which is a much more practical, industrially achievable temperature.\u201d<\/p>\n<\/blockquote>\n\n\n

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\"Schematic\"\/
The electrocatalytic-thermocatalytic tandem strategy for CNF production circumvents thermodynamic constraints by combining the co-electrolysis of CO2<\/sub> and water into syngas (CO and H2<\/sub>) with a subsequent thermochemical process under mild conditions (370-450 \u00b0C, ambient pressure). This yields a high CNF production rate. The optimal synergy of iron-cobalt (FeCo) alloy and extra metallic Co enhanced the dissociative activation of syngas, promoting carbon-carbon bond formation for CNF production. \u00a9<\/strong> Zhenhua Xie\/Brookhaven National Laboratory and Columbia University<\/figcaption><\/figure><\/div>\n\n\n

The tandem two-step <\/h3>\n\n\n\n

The trick was to break the reaction into stages and to use two different types of catalysts\u2014materials that make it easier for molecules to come together and react.<\/p>\n\n\n\n

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\u201cIf you decouple the reaction into several sub-reaction steps you can consider using different kinds of energy input and catalysts to make each part of the reaction work,\u201d said Brookhaven Lab and Columbia research scientist Zhenhua Xie, lead author on the paper.<\/p>\n<\/blockquote>\n\n\n\n

The scientists started by realizing that carbon monoxide (CO) is a much better starting material than CO2<\/sub> for making carbon nanofibers (CNF). Then they backtracked to find the most efficient way to generate CO from CO2<\/sub>.<\/p>\n\n\n\n

Earlier work from their group steered them to use a commercially available electrocatalyst<\/em> made of palladium supported on carbon. Electrocatalysts drive chemical reactions using an electric current. In the presence of flowing electrons and protons, the catalyst splits both CO2<\/sub> and water (H2<\/sub>O) into CO and H2<\/sub>.<\/p>\n\n\n\n

For the second step, the scientists turned to a heat-activated thermocatalyst<\/em> made of an iron-cobalt alloy. It operates at temperatures around 400 degrees Celsius, significantly milder than a direct CO2<\/sub>-to-CNF conversion would require. They also discovered that adding a bit of extra metallic cobalt greatly enhances the formation of the carbon nanofibers.<\/p>\n\n\n\n

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\u201cBy coupling electrocatalysis and thermocatalysis, we are using this tandem process to achieve things that cannot be achieved by either process alone,\u201d Chen said.<\/p>\n<\/blockquote>\n\n\n

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\"High-resolution
High-resolution transmission electron microscopy (TEM) shows the tip of the resulting carbon nanofiber (left) on the iron-cobalt\/cerium oxide (FeCo\/CeO2<\/sub>) thermocatalyst. Scientists mapped the structure and chemical composition of newly formed carbon nanofibers (right) using scanning transmission electron microscopy (STEM), high-angle annular dark field (HAADF) imaging, and energy-dispersive x-ray spectroscopy (EDS) (scale bar represents 8 nanometers). The images show that the nanofibers are made of carbon (C), and reveal that the catalytic metals, iron (Fe) and cobalt (Co), are pushed away from the catalytic surface and accumulate at the tip of the nanofiber. \u00a9<\/strong> Center for Functional Nanomaterials\/Brookhaven National Laboratory<\/figcaption><\/figure><\/div>\n\n\n

Catalyst characterization<\/h3>\n\n\n\n

To discover the details of how these catalysts operate, the scientists conducted a wide range of experiments. These included computational modeling studies, physical and chemical characterization studies at Brookhaven Lab\u2019s National Synchrotron Light Source II<\/a> (NSLS-II)\u2014using the Quick X-ray Absorption and Scattering<\/a> (QAS) and Inner-Shell Spectroscopy<\/a> (ISS) beamlines\u2014and microscopic imaging at the Electron Microscopy<\/a> facility at the Lab\u2019s Center for Functional Nanomaterials<\/a> (CFN).<\/p>\n\n\n\n

On the modeling front, the scientists used \u201cdensity functional theory\u201d (DFT) calculations to analyze the atomic arrangements and other characteristics of the catalysts when interacting with the active chemical environment.<\/p>\n\n\n\n

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\u201cWe are looking at the structures to determine what are the stable phases of the catalyst under reaction conditions,\u201d explained study co-author Ping Liu of Brookhaven\u2019s Chemistry Division who led these calculations. \u201cWe are looking at active sites and how these sites are bonding with the reaction intermediates. By determining the barriers, or transition states, from one step to another, we learn exactly how the catalyst is functioning during the reaction.\u201d<\/p>\n<\/blockquote>\n\n\n\n

X-ray diffraction and x-ray absorption experiments at NSLS-II tracked how the catalysts change physically and chemically during the reactions. For example, synchrotron x-rays revealed how the presence of electric current transforms metallic palladium in the catalyst into palladium hydride, a metal that is key to producing both H2<\/sub> and CO in the first reaction stage.<\/p>\n\n\n\n

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For the second stage, \u201cWe wanted to know what\u2019s the structure of the iron-cobalt system under reaction conditions and how to optimize the iron-cobalt catalyst,\u201d Xie said. The x-ray experiments confirmed that both an alloy of iron and cobalt plus some extra metallic cobalt are present and needed to convert CO to carbon nanofibers.<\/p>\n\n\n\n

\u201cThe two work together sequentially,\u201d said Liu, whose DFT calculations helped explain the process.<\/p>\n\n\n\n

\u201cAccording to our study, the cobalt-iron sites in the alloy help to break the C-O bonds of carbon monoxide. That makes atomic carbon available to serve as the source for building carbon nanofibers. Then the extra cobalt is there to facilitate the formation of the C-C bonds that link up the carbon atoms,\u201d she explained.<\/p>\n<\/blockquote>\n\n\n\n

\"Zhenhua

<\/a>Brookhaven Lab members of the research team: Zhenhua Xie (Brookhaven\/Columbia), Ping Liu (Brookhaven), Erwei Huang (Brookhaven), Sooyeon Hwang (Brookhaven), Jingguang Chen (Brookhaven\/Columbia). \u00a9<\/strong> Roger Stoutenburgh\/Brookhaven National Laboratory<\/figcaption><\/figure>\n\n\n\n

Recycle-ready, carbon-negative<\/h3>\n\n\n\n
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\u201cTransmission electron microscopy (TEM) analysis conducted at CFN revealed the morphologies, crystal structures, and elemental distributions within the carbon nanofibers both with and without catalysts,\u201d said CFN scientist and study co-author Sooyeon Hwang.<\/p>\n<\/blockquote>\n\n\n\n

The images show that, as the carbon nanofibers grow, the catalyst gets pushed up and away from the surface. That makes it easy to recycle the catalytic metal, Chen said.<\/p>\n\n\n\n

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\u201cWe use acid to leach the metal out without destroying the carbon nanofiber so we can concentrate the metals and recycle them to be used as a catalyst again,\u201d he said.<\/p>\n<\/blockquote>\n\n\n\n

This ease of catalyst recycling, commercial availability of the catalysts, and relatively mild reaction conditions for the second reaction all contribute to a favorable assessment of the energy and other costs associated with the process, the researchers said.<\/p>\n\n\n\n

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\u201cFor practical applications, both are really important\u2014the CO2<\/sub> footprint analysis and the recyclability of the catalyst,\u201d said Chen. \u201cOur technical results and these other analyses show that this tandem strategy opens a door for decarbonizing CO2<\/sub> into valuable solid carbon products while producing renewable H2<\/sub>.\u201d<\/p>\n<\/blockquote>\n\n\n\n

If these processes are driven by renewable energy, the results would be truly carbon-negative, opening new opportunities for CO2<\/sub> mitigation.<\/p>\n\n\n\n

This research was supported by the DOE Office of Science (BES). The DFT calculations were performed using computational resources at CFN and at the National Energy Research Scientific Computing Center<\/a> (NERSC) at DOE\u2019s Lawrence Berkeley National Laboratory<\/a>. NSLS-II, CFN, and NERSC are DOE Office of Science user facilities.<\/p>\n\n\n\n

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. <\/p>\n\n\n\n

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