• Researchers have combined gold nanoparticles (in light red) with copper nanoparticles (in light green) to form hybrid nanoparticles (dark red), which they turned into powder (foreground) to catalyze carbon dioxide reduction.

    Photo: Zhichuan Xu

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  • An electron microscopy image of hybrid gold/copper nanoparticles.

    Image: Zhichuan Xu

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Hybrid copper-gold nanoparticles convert CO2

May reduce greenhouse gas emissions


Copper — the stuff of pennies and tea kettles — is also one of the few metals that can turn carbon dioxide into hydrocarbon fuels with relatively little energy. When fashioned into an electrode and stimulated with voltage, copper acts as a strong catalyst, setting off an electrochemical reaction with carbon dioxide that reduces the greenhouse gas to methane or methanol.

Various researchers around the world have studied copper’s potential as an energy-efficient means of recycling carbon dioxide emissions in powerplants: Instead of being released into the atmosphere, carbon dioxide would be circulated through a copper catalyst and turned into methane or methanol — which could then power the rest of the plant by combustion, or be converted to chemical products such as ethylene. Such a system, paired with energy from solar or wind, could vastly reduce greenhouse gas emissions from coal-fired and natural gas-powered plants.

But copper is temperamental: easily oxidized, as when an old penny turns green. As a result, the metal is unstable, which can significantly slow its reaction with carbon dioxide and produce unwanted byproducts such as carbon monoxide and formic acid.

Now researchers at MIT have come up with a solution that may further reduce the energy needed for copper to convert carbon dioxide, while also making the metal much more stable. The group has engineered tiny nanoparticles of copper mixed with gold, which is resistant to corrosion and oxidation. The researchers observed that just a touch of gold makes copper much more stable. In experiments, they coated electrodes with the hybrid nanoparticles and found that much less energy was needed for these engineered nanoparticles to react with carbon dioxide, compared to nanoparticles of pure copper.

A paper detailing the results will appear in the journal Chemical Communications; the research was funded by the National Science Foundation. Co-author Kimberly Hamad-Schifferli of MIT says the findings point to a potentially energy-efficient means of reducing carbon dioxide emissions from powerplants.

“You normally have to put a lot of energy into converting carbon dioxide into something useful,” says Hamad-Schifferli, an associate professor of mechanical engineering and biological engineering. “We demonstrated hybrid copper-gold nanoparticles are much more stable, and have the potential to lower the energy you need for the reaction.”

Going small

The team chose to engineer particles at the nanoscale in order to “get more bang for their buck,” Hamad-Schifferli says: The smaller the particles, the larger the surface area available for interaction with carbon dioxide molecules. “You could have more sites for the CO2 to come and stick down and get turned into something else,” she says.

Hamad-Schifferli worked with Yang Shao-Horn, the Gail E. Kendall Associate Professor of Mechanical Engineering at MIT, postdoc Zhichuan Xu and Erica Lai ’14. The team settled on gold as a suitable metal to combine with copper mainly because of its known properties. (Researchers have previously combined gold and copper at much larger scales, noting that the combination prevented copper from oxidizing.)

To make the nanoparticles, Hamad-Schifferli and her colleagues mixed salts containing gold into a solution of copper salts. They heated the solution, creating nanoparticles that fused copper with gold. Xu then put the nanoparticles through a series of reactions, turning the solution into a powder that was used to coat a small electrode.

To test the nanoparticles’ reactivity, Xu placed the electrode in a beaker of solution and bubbled carbon dioxide into it. He applied a small voltage to the electrode, and measured the resulting current in the solution. The team reasoned that the resulting current would indicate how efficiently the nanoparticles were reacting with the gas: If CO2 molecules were reacting with sites on the electrode — and then releasing to allow other CO2 molecules to react with the same sites — the current would appear as a certain potential was reached, indicating regular “turnover.” If the molecules monopolized sites on the electrode, the reaction would slow down, delaying the appearance of the current at the same potential.

The team ultimately found that the potential applied to reach a steady current was much smaller for hybrid copper-gold nanoparticles than for pure copper and gold — an indication that the amount of energy required to run the reaction was much lower than that required when using nanoparticles made of pure copper.

Going forward, Hamad-Schifferli says she hopes to look more closely at the structure of the gold-copper nanoparticles to find an optimal configuration for converting carbon dioxide. So far, the team has demonstrated the effectiveness of nanoparticles composed of one-third gold and two-thirds copper, as well as two-thirds gold and one-third copper.

Hamad-Schifferli acknowledges that coating industrial-scale electrodes partly with gold can get expensive. However, she says, the energy savings and the reuse potential for such electrodes may balance the initial costs.

“It’s a tradeoff,” Hamad-Schifferli says. “Gold is obviously more expensive than copper. But if it helps you get a product that’s more attractive like methane instead of carbon dioxide, and at a lower energy consumption, then it may be worth it. If you could reuse it over and over again, and the durability is higher because of the gold, that’s a check in the plus column.”


Topics: Biological engineering, Carbon dioxide, Climate change, Energy, Greenhouse gases, Mechanical engineering, Nanoparticles, Nanoscience and nanotechnology

Comments

You indicated possible use in stationary applications. What is prohibitive for mobile appllications - cars, busses, trains?
"....carbon dioxide would be circulated through a copper catalyst and turned into methane — which could then power the rest of the plant." Methane is a more potent greenhouse gas than CO2, so releasing the methane is not a viable option. If the methane is used to power the rest of the plant the methane is converted to ..... CO2! So I guess we would use the process again to convert it back to methane. So it is either a perpetual motion machine, or something that just wastes energy converting CO2 to methane and back to CO2 again.
This seems to bee a perpetuum mobile using hydrocarbons to create electricity and CO2, and then converting the same CO2 back to hydrocarbons. It must be an April fools joke
My crude geuess is: You missed the publication date for this release. I bet intended was 2012-04-01. Alternatively you might have missed the paragraph on the 4th Law of thermodynamics revealing that the First Law will be rewritten.
Keep going on your work. What is wrong with a “perpetual motion machine” when its main product is electricity? This recycling system attacks emissions in powerplants/electricity. Scrubbing emission waste by turning carbon dioxide into fuel to power its own machinery becomes self-sustaining: utilizing CO2 as its raw material. Hamad-Schifferli/ economic issues: “If you could reuse it over and over again, and the durability is higher because of the gold, that’s a check in the plus column” shows a practical side missing from academic techies. Her concern is unwarranted. Gold will still be there. Gold has economic and environmental benefits that other elements lack: immunity to oxidation. Only man-made chemicals impact gold. Car toxic emissions are tamed with platinum scrubbers; this idea may lead to social benefits for power plants necessary now and in the future. Driving on the Los Angeles freeways in 1967, we could not see past three telephone poles due to smog. Go researchers.
I agree with the criticism that using this research as a means of cycling between CO2 and CH4 for energy efficiency purposes is fundamentally flawed, as each cycle no matter how close to ideal it is made must lose energy. However, the research claim is for a lower energy method of using copper/gold nanoparticles to catalyze this rxn compared to plain copper. The "reuse" I believe Hamad-Schifferli is referring to in the last paragraph is the reuse of the copper catalyst (which ordinarily would be fouled). The article is perhaps misleadingly written. In a coal-powered plant, this would be beneficial compared to merely venting the CO2 or attempting to sequester it. CH4 has greater applications than CO2. The same amount of CO2 must eventually leave the system at some point, but it opens up the potential to redirect the CH4 into producing fertilizer or as feedstock into other chemical processes (provided it isn't released, since as mentioned it is a worse GHG than CO2).
Let us temper our enthusiasm here. It's these kinds of press releases that give public relations offices bad reps and make the S&E faculty look foolish Did anybody ever do the thermochemistry?? If all you do is recycle methane the reaction will be thermoneutral or worse depending on the energy cost for your hydrogen (from water?? Graetzel and friends have been chasing catalysts for splitting water for decades with scientific but not economic success) and if you have a free source of hydrogen, why not just burn it? The only thing that CO2 cracking makes sense for is production of higher value hydrocarbons (e.g. plastic/solvents, auto fuel, etc.) and that has huge economic barriers as well as issues of volume. This is press release abuse at it's worst. Premature is a very kind description.
<b><i>Editor's note: The text has been updated to address some concerns noted in the comments section. Here, as well, is a note from the researchers</i></b> Yes, you have to use energy to convert CO2, so it is not a perpetual motion machine. Rather, it is a good way to convert something that is environmentally bad into something useful-- and this comes at an energetic cost of course. If a plant wanted to use the methane it made by CO2 reduction they could, but it is at a cost ($ and energetically). However, the CO2 reduction is a long-term complementary technique to the energy production those by fossil fuel combustion. It minimizes the emission of CO2 by converting them back to chemical fuels, and of course this process needs external energy. However, there are many energy sources can be choosed to power this process, not the energy originally generated from the fuel combustion while generating CO2. For example, using solar cell generating electricity and then store the electricity energy in form of chemical fuels by CO2 electrochemical reduction process. That means solar energy was store in form of chemicals, and that is actually what we want to learn from the nature process, photosynthsis by plants. This technique is not just making a C circle between fossil fuels and CO2 and wasting energy from the origin of fossil fuels. In addition, although methane is a bad greenhouse gas it can be converted into more viable fuel products (ethylene). - Zhichuan Xu
Please don't try and double down. You really don't have a grasp on the issue as the comments have shown and your press release was torn to bits by just about anyone who read it no matter what their opinion on climate change.
I would suggest thinking toward fuel-cell development with this technology because it closes a chemical cycle while remaining an overall energy-losing process. In fuel cells, the CH4 can be returned to CO2 with a net output of (thermal and electric) energy. Upon recharging, the fuel cell can reconvert its CO2 to CH4. You may have to consider constituent containment such as pressurized gas bottles to contain chemicals at different phases of the charge-discharge cycle. Additionally this type of storage may render the reagents available for other buffering/temporary applications including catalysis within seperate reactions, carried out mid-cycle outside of the fuel-cell system. Think of the overall system as perhaps a big electric battery, whose constituent contents may be temporarily repurposed and then returned to service as needed. A good basis for perhaps a space or submarine technology for energy storage and transduction.
The CO2 produced by power plants is heavily diluted with nitrogen, oxygen and moisture (amongst other things). For this technology to produce a 'pure' fuel you would need near pure CO2, which can only be achieved using a carbon capture technology. Furthermore, using electrical energy to convert CO2 into CH4 is effectively taking 'high potential energy' and converting it into 'low potential energy' which can only be reversed back to electrical power with a ~60% efficiencly (in a CCGT for example). "Instead of being released into the atmosphere, carbon dioxide would be circulated through a copper catalyst and turned into methane or methanol — which could then power the rest of the plant by combustion" The last bit of that actually suggests taking electrical energy, converting it to CH4 then burning it to make more power - doesn't add up. I like the idea of storing solar energyinto fuel, but at what efficiency loss? Some battery technologies can do that today at higher efficiencly.
This work represents a significant increment towards a storage solution for electrical energy created during low demand periods, especially by non-fossil powered generation. The pressing need is for fuels, liquid fuels in particular, for nonstationary uses. With consideration to transmission costs and losses, of both CO2 and electricity, it is likely that application will first make sense at coal fired plants which are sited near windpower, solar power, nuclear or geothermal plants. The use of 'surplus' electricity to synthesize liquid fuels will help offset the use of fossil fuels and reduce energy imports compared to what they would otherwise be.
three years ago I wrote a column talking about CO@ conversion in power plants to economically useful carbon nanotubes. The issue was the energy needed to get CO2 to C and O2. These catalysts go a long way toward economically viable systems. Using methane for CNT product is a standard process and with the power already in the plane augmented by the resultant O2, you can produce CNT's economically for incorporation in Concrete, plastics, Cement, etc... local construction applications justifying the process. alan shalleck, Pres. nanoclarity LLC
The Space Shuttle used molecular seive technology to separate CO2 from a mixed-gas stream. There may be significant scalability opportunities for this approach to obtaining a pure stream of CO2 for use in this catalytic process. Overall, please keep up the research in this direction; every step we take to learn more toward an efficient means to control atmospheric CO2 levels is vital to our survival. And we have a ways to go yet.
That was exactly what I was thinking. There are many hurdles from what I understand though. Firstly, The system would have to be lightweight. Leaks (liquid and gas) would have to be either reduced or completely sealed. The electricity required to power the conversion would have to come from somewhere (like solar panels on the roof and solar windows). the battery in the car would be bigger and heavier to hold the electricity gained by the solar panel before being used to convert the CO2. And then the question has to be asked, "is it worth going through all this trouble to get the more explosive output of a combustion engine a "green" vehicle, when the electricity from the solar panel can go towards an electric vehicle?" I will admit this idea would remove the notorious "range anxiety" that many owners of electric vehicles face today.
All that is being said is that the activation energy (Ea) of CO2+2H20 = CH4+202 is being reduced by the copper catalyst, nothing else. this can be used in many ways. It can be used to store energy. Because electric engines struggle to reach the output of combustion engines and CO2 is so readily available in a combustion engine, then the reaction is usefull. The fuel can be recycled constantly as long as electricity is available. You then get the output of a combustion engine with the clean environmental conscience of an electric car. A vehicle powered by a combustion engine is safer in my opinion also. Wires running through electric cars have a lot of current and "the jaws of life" can not be used on a wrecked electric vehicle because of this. That may have changed since I learned that bit of information; so, tell me if I'm wrong. Also, this article was posted before all of the research was done. They are still working on it. So, to quote, "to what use is a new born child?"
Because certain governments (EU and US etc) believe CO2 is in some way harmful, we have crackpots covering huge swathes of land and water with wind farms. We also have a situation in which the cheapest, most efficioent forms of energy production are being demonised because they produce CO2. This system if it can be made commercially affordable can satisfy the need for cheap efficient energy and also keep the crackpots happy at the same time. CO2 is plant food folks and it does not cause warming ^.^
Yes, this is potentially useful research that could help mitigate urgent problems related to CO2 production by industrial processes. However, as interesting as the research and future utility of the technology is, perhaps the responses to the summary reported here are even more important and interesting: We see a reactionary comment by one who does not recognize our critical environmental problems, and blames government. We see others who are weak critical readers, or perhaps inconsistent readers when they scan technology summaries, and did not notice or understand the lines that referred to the need for energy input. ...or did I miss something that should have told me that the reaction could be auto-catalytic in nano particles of gold-copper alloys on some sort of supporting matrix. Sometimes, too, people's hope for panaceas lead them to understand those things not implied, and so think that there would be net energy gains in the process.
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