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This scanning electron microscope image shows the carbon cathode of a carbon-dioxide-based battery made by MIT researchers, after the battery was discharged. It shows the buildup of carbon compounds on the surface, composed of carbonate material that could be derived from power plant emissions, compared to the original pristine surface (inset) Courtesy of the researchers

Lithium-based battery could make use of greenhouse gas before it ever gets into the atmosphere.

A new type of battery developed by researchers at MIT could be made partly from carbon dioxide captured from power plants. Rather than attempting to convert carbon dioxide to specialized chemicals using metal catalysts, which is currently highly challenging, this battery could continuously convert carbon dioxide into a solid mineral carbonate as it discharges.

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While still based on early-stage research and far from commercial deployment, the new battery formulation could open up new avenues for tailoring electrochemical carbon dioxide conversion reactions, which may ultimately help reduce the emission of the greenhouse gas to the atmosphere.

battery-atmosphereRead Also:  Scientists Have Created Batteries Using Carbon Dioxide From The Atmosphere Which Could Replace Phone And Electric Car Batteries

 

 

 

The battery is made from lithium metal, carbon, and an electrolyte that the researchers designed. The findings are described today in the journal Joule, in a paper by assistant professor of mechanical engineering Betar Gallant, doctoral student Aliza Khurram, and postdoc Mingfu He.

Currently, power plants equipped with carbon capture systems generally use up to 30 percent of the electricity they generate just to power the capture, release, and storage of carbon dioxide. Anything that can reduce the cost of that capture process, or that can result in an end product that has value, could significantly change the economics of such systems, the researchers say.

However, “carbon dioxide is not very reactive,” Gallant explains, so “trying to find new reaction pathways is important.” Generally, the only way to get carbon dioxide to exhibit significant activity under electrochemical conditions is with large energy inputs in the form of high voltages, which can be an expensive and inefficient process. Ideally, the gas would undergo reactions that produce something worthwhile, such as a useful chemical or a fuel. However, efforts at electrochemical conversion, usually conducted in water, remain hindered by high energy inputs and poor selectivity of the chemicals produced.

Gallant and her co-workers, whose expertise has to do with nonaqueous (not water-based) electrochemical reactions such as those that underlie lithium-based batteries, looked into whether carbon-dioxide-capture chemistry could be put to use to make carbon-dioxide-loaded electrolytes — one of the three essential parts of a battery — where the captured gas could then be used during the discharge of the battery to provide a power output.

This approach is different from releasing the carbon dioxide back to the gas phase for long-term storage, as is now used in carbon capture and sequestration, or CCS. That field generally looks at ways of capturing carbon dioxide from a power plant through a chemical absorption process and then either storing it in underground formations or chemically altering it into a fuel or a chemical feedstock.

Instead, this team developed a new approach that could potentially be used right in the power plant waste stream to make material for one of the main components of a battery.

While interest has grown recently in the development of lithium-carbon-dioxide batteries, which use the gas as a reactant during discharge, the low reactivity of carbon dioxide has typically required the use of metal catalysts. Not only are these expensive, but their function remains poorly understood, and reactions are difficult to control.

By incorporating the gas in a liquid state, however, Gallant and her co-workers found a way to achieve electrochemical carbon dioxide conversion using only a carbon electrode. The key is to pre-activate the carbon dioxide by incorporating it into an amine solution.

“What we’ve shown for the first time is that this technique activates the carbon dioxide for more facile electrochemistry,” Gallant says. “These two chemistries — aqueous amines and nonaqueous battery electrolytes — are not normally used together, but we found that their combination imparts new and interesting behaviors that can increase the discharge voltage and allow for sustained conversion of carbon dioxide.”

They showed through a series of experiments that this approach does work, and can produce a lithium-carbon dioxide battery with voltage and capacity that are competitive with that of state-of-the-art lithium-gas batteries. Moreover, the amine acts as a molecular promoter that is not consumed in the reaction.

The key was developing the right electrolyte system, Khurram explains. In this initial proof-of-concept study, they decided to use a nonaqueous electrolyte because it would limit the available reaction pathways and therefore make it easier to characterize the reaction and determine its viability. The amine material they chose is currently used for CCS applications, but had not previously been applied to batteries.

factory-air-pollution-environment-smoke-shutterstock_130778315-34gj4r8xdrgg8mj9r25a0wThis early system has not yet been optimized and will require further development, the researchers say. For one thing, the cycle life of the battery is limited to 10 charge-discharge cycles, so more research is needed to improve rechargeability and prevent degradation of the cell components. “Lithium-carbon dioxide batteries are years away” as a viable product, Gallant says, as this research covers just one of several needed advances to make them practical.

But the concept offers great potential, according to Gallant. Carbon capture is widely considered essential to meeting worldwide goals for reducing greenhouse gas emissions, but there are not yet proven, long-term ways of disposing of or using all the resulting carbon dioxide. Underground geological disposal is still the leading contender, but this approach remains somewhat unproven and may be limited in how much it can accommodate. It also requires extra energy for drilling and pumping.

The researchers are also investigating the possibility of developing a continuous-operation version of the process, which would use a steady stream of carbon dioxide under pressure with the amine material, rather than a preloaded supply the material, thus allowing it to deliver a steady power output as long as the battery is supplied with carbon dioxide. Ultimately, they hope to make this into an integrated system that will carry out both the capture of carbon dioxide from a power plant’s emissions stream, and its conversion into an electrochemical material that could then be used in batteries. “It’s one way to sequester it as a useful product,” Gallant says.

“It was interesting that Gallant and co-workers cleverly combined the prior knowledge from two different areas, metal-gas battery electrochemistry and carbon-dioxide capture chemistry, and succeeded in increasing both the energy density of the battery and the efficiency of the carbon-dioxide capture,” says Kisuk Kang, a professor at Seoul National University in South Korea, who was not associated with this research.

“Even though more precise understanding of the product formation from carbon dioxide may be needed in the future, this kind of interdisciplinary approach is very exciting and often offers unexpected results, as the authors elegantly demonstrated here,” Kang adds.

MIT’s Department of Mechanical Engineering provided support for the project.

GH Gas 031716 global-climate-changeHybrid materials developed at Berkeley Lab could lead to cheaper ways to reduce power plant greenhouse gas emissions

In this animation, exhaust from a power plant contacts a hybrid membrane recently developed at Berkeley Lab. The membrane’s carbon dioxide highways (yellow) enable the rapid flow of carbon dioxide (red and white molecules) while maintaining selectivity over nitrogen (blue molecules). The membrane is eight times more carbon dioxide permeable than a polymer-only membrane. (Credit: Berkeley Lab)

A new, highly permeable carbon capture membrane developed by scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) could lead to more efficient ways of separating carbon dioxide from power plant exhaust, preventing the greenhouse gas from entering the atmosphere and contributing to climate change.

The researchers focused on a hybrid membrane that is part polymer and part metal-organic framework, which is a porous three-dimensional crystal with a large internal surface area that can absorb enormous quantities of molecules.

In a first, the scientists engineered the membrane so that carbon dioxide molecules can travel through it via two distinct channels. Molecules can travel through the polymer component of the membrane, like they do in conventional gas-separation membranes. Or molecules can flow through “carbon dioxide highways” created by adjacent metal-organic frameworks.

Initial tests show this two-route approach makes the hybrid membrane eight times more carbon dioxide permeable than membranes composed only of the polymer. Boosting carbon dioxide permeability is a big goal in efforts to develop carbon capture materials that are energy efficient and cost competitive.

The research is the cover article of the March issue of the journalEnergy & Environmental Science.

“In our membrane, some CO2 molecules get an express ride through the highways formed by metal-organic frameworks, while others take the polymer pathway. This new approach will enable the design of higher performing gas separation membranes,” says Norman Su, a graduate student in the Chemical and Biomolecular Engineering Department at UC Berkeley and a user at the Molecular Foundry.

He conducted the research with Jeff Urban, Facility Director of the Inorganic Nanostructures Facility at the Molecular Foundry, and a team of scientists that included staff at the Advanced Light Source.

Capturing carbon emissions from electric power plants and other sources is a hot research topic because there’s a lot of room for improvement. The conventional way of separating carbon dioxide from flue gas is amine adsorption, which isn’t economical at scale because it adds significant capital cost and reduces the electrical output of power plants.

Scientists are exploring polymer membranes as a more energy efficient alternative to amine adsorption. These membranes are relatively inexpensive and easy to work with, but current commercial membranes have low carbon dioxide permeability. To overcome this, scientists have developed hybrid membranes that are part polymer and part metal-organic framework. These hybrids harness the carbon dioxide selectivity of metal-organic frameworks while maintaining the processability of polymers.

But, until now, scientists have not been able to engineer hybrid membranes with enough metal-organic frameworks to form continuous channels through the membrane. This means that, somewhere in a carbon dioxide molecule’s journey through the membrane, the molecule must contact the polymer. This constrains the molecule’s transport to the polymer.

In this latest research, Berkeley Lab scientists have developed a hybrid membrane in which metal-organic frameworks account for 50 percent of its weight, which is about 20 percent more than other hybrid membranes. Previously, the mechanical stability of a hybrid membrane limited the amount of metal-organic frameworks that could be packed in it.

“But we got our membrane to 50 weight percent without compromising its structural integrity,” says Su.

And 50 weight percent appears to be the magic number. At that threshold, there are so many metal organic frameworks in the membrane that they form a continuous network of highways through the membrane. When that happens, the hybrid membrane switches from having a single channel to transport carbon dioxide, in which the molecules must go through the polymer, to two channels, in which the molecules can either move through the polymer or through the metal-organic framework highways.

“This is the first hybrid polymer-MOF membrane to have these dual transport pathways, and it could be a big step toward more competitive carbon capture processes,” says Su.

In addition to fabricating the hybrid membrane at the Molecular Foundry, the scientists analyzed the material at beamline 12.2.2 of the Advanced Light Source.

The research was supported by the Department of Energy’s Office of Science, Berkeley Lab’s Laboratory-Directed Research and Development Program, and the Department of Defense.

The Advanced Light Source and the Molecular Foundry are DOE Office of Science User Facilities located at Berkeley Lab.

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Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s 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. For more information, please visit science.energy.gov

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