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MIT researchers engineer stable copper-gold nanoparticle catalysts for lower energy consumption CO2 reduction

Copper nanoparticles (NPs) are attractive catalysts for chemical reactions including the reduction of CO2 to methane or methanol. However, copper is easily oxidized; 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. For NPs, this can be greatly accelerated because of the high surface-to-volume ratios, and thus can deteriorate catalyst lifetime.

Researchers at MIT engineered nanoparticles of copper (Cu) mixed with gold (Au), which is resistant to corrosion and oxidation, and measured the oxidation rate of the AuCu NPs as a function of composition. They found that increasing the percentage of gold improves the catalyst’s stability, and also found that the overpotential of AuCU NPs for reduction in the presence of CO2 is lower than that for Au or Cu NPs alone. As a result of the findings, the researchers suggest that AuCu NPs could be a promising catalyst to lower the energy consumption of CO2 reduction.

One solution [to the problem of Cu oxidation] is to alloy Cu with stabilizing metals...Alloys with Au are desirable because bulk Au and Cu form a solid solution, so alloy composition is tunable, enabling optimization of optical and/or catalytic properties. A few of solution-based approaches for synthesizing AuCu NPs have been reported, but studies in how composition, structure, and size affect NP activity and optical properties have been limited. Because oxidation of Cu is facile, and can be accelerated in high surface area systems like NPs, an important property that needs to be understood is the stability of AuCu NPs with respect to oxidation, which has not been reported.

Here we study the oxidation of AuCu NPs as a function of composition. We find that the Cu oxidation rate depends on NP composition, where increasing Au% improves stability and alloying Au with Cu potentially lowers the overpotential for CO2 reduction.

—Xu et al.

A paper detailing the results is in press in the RSC 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.

Hamad-Schifferli worked with Yang Shao-Horn, the Gail E. Kendall Associate Professor of Mechanical Engineering at MIT, postdoc Zichuan Xu and Erica Lai ‘14. 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 mdash;and then releasing to allow other CO2 molecules to react with the same sites mdash;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.

Electrochemical CO2 reduction is a complex process producing various surface and solution products, and faradic efficiency of certain products such as methane and methanol is typically used to evaluate catalyst selectivity and activity. While CV cannot definitively evaluate activity, the positive-shift of the onset potential indicates that alloying Au with Cu has potential to lower the energy used for the electrochemical CO2 reduction, which must be considered in catalyst evaluation.

These results show that NP stability can be tuned by composition, which could impact applications using AuxCuy alloys, particularly catalysis and optical applications.

—Xu et al.

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.

Resources

  • Z. Xu, E. Lai, Y. Shao-Horn, and K. Hamad-Schifferli (2012) Compositional dependence of the stability of AuCu alloy nanoparticles. ChemComm, in press.

Comments

A D

I said many time to do fuels (methane or methanol) with the co2 that is expelled from most chimneys and recirculate this new fuel at the input or sell this fuel to consumers, is it clear now. This is not weird science. Natural gas and coal electric power plants could run indefinately with the same fuel that is reconverted again and again and also it eliminate completely pollution and fuel cost. All it take is this new process. Also petrol prices will shrink so i will be able to drive 5 to 10 mph faster then i actually do because i slow down to consume less because gas is costly, less time on the road decrease traffic so everyone is happy.

Arne

A.D. says:

"Natural gas and coal electric power plants could run indefinately with the same fuel that is reconverted again and again and also it eliminate completely pollution and fuel cost."

What you are describing is a perpetuum mobile. Just like you can find 1000's of videos on YouTube in which inventors claim to have invented such a device in their garage. Although the latest fad in this segment seems to be 'cold fusion'.

Study the law of conservation of energy and you'll understand why it is pretty ridiculous what you are saying.

SJC

The world can be divided between scientists and believers. Some people believe in perpetual motion, scientists can show evidence that there is NO such thing.

When you think of how belief and science have been at odds with one another throughout history, it is a wonder that we made any progress at all. Belief tries to eliminate logic and evidence, you are not a team player thus you must be disruptive and have a hidden agenda.

HarveyD

There are more naysayers, brain washed believers, followers, addicts and speculators with agenda than scientists and real believers.

That's how so many drove 8000+ lbs Hummers and 21-ft. long boats on wheels.

A D

The fuel doesn't dissapear, it is transformed in co2. So if we tranform the co2 back to fuel then we recirculate it back at the input for a complete system with endless energy over time without pollution. Why waste co2 and vent it to the outside ?? Stop the brainwash of the fuel resellers. Nostradamus predicted it, the crisis come from the people that argue that. After one person will teach it to the mass then we will have almost free endless non-polluting electricity and hydrogen for mobile application like cars, trucks, trains, ships.

SJC

I think two people post as AD.

Roger Pham

@A D,
It may be more energy-efficient and cost-effective to build a H2 pipeline system and H2 underground storage system for long-term storage of renewable energy.

Incorporating H2 into CO2 for the synthesis of hydrocarbon would cost more than building a H2 storage system, so the idea in this article is a very long shot, way into the future.

Waste biomass can serve as a source of carbon-based energy as well as organic chemical feedstock. Hydrogen enrichment of waste biomass using renewable-energy hydrogen is a more compact and more transportable way of storing renewable energy.

Quit burning coal and leave it on the ground is a much more cost-effective than removing CO2 out of the air synthetically, or the ridiculous scheme of CO2 sequestration from coal combustion.

Roger Pham

Furthermore, gold is quite expensive for the electrochemical reduction of CO2! A steady source of high-concentration CO2 is not easy to have, either. We are talking about going against entropy to pull CO2 out of thin air.

Electrolysis of water to produce H2 is much easier, since water is very cheap and easy to obtain than CO2, and electrolysis of water no longer requires Platinum.

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