Cleaner air with gold and copper

Researchers at MIT have discovered that a mix of gold and copper can turn power-plant's CO2 emission into hydrocarbon fuels.
Written by Ina Muri, Weekend Editor

Researchers at MIT have discovered a way to make copper turn carbon dioxide into hydrocarbon fuels, with help of just a little bit of gold.

When copper is stimulated with voltage, it acts as a strong catalyst that sets off an electrochemical reaction with carbon dioxide that reduces the greenhouse gas to methane or methanol. But the problem was that copper is temperamental and oxidize too easily. Copper is inherently unstable, which significantly slows down the reaction with carbon dioxide by producing unwanted byproducts.

Various researchers around the world have studied copper's potential as an energy-efficient means of recycling carbon dioxide emissions in power plants  for years. Instead of being released into the atmosphere, carbon dioxide would be circulated through a copper catalyst and turned into methane or methanol. In return, methane and methanol could power the rest of the plant by combustion, or be converted to chemical products such as ethylene. A system like that could vastly reduce greenhouse gas emissions form coal-fired and natural gas-powered plants.

MIT's Kimberly Hamad- Schefferli, an associate professor of mechanical engineering and biological engineering, and her team have come up with a solution of using gold to reduce the energy needed for copper to convert carbon dioxide. Since gold is resistant to corrosion and oxidation, the group has engineered a mix of tiny nano-particles of gold with the copper. They observed that just a touch of gold makes copper much more stable. In these experiments, they coated electrodes with the hybrid nano-particles to react with carbon dioxide, compared to nano-particles of pure copper.

"You normally have to put a lot of energy into converting carbon dioxide into something useful," Hamad-Schifferli said. " We demonstrated that a hybrid of copper-gold nano particles are much more stable, and have the potential to lower the energy you need for the reaction."

The team chose the engineered particles at the nanoscale in order to "get more bang for their buck," Hamad- Schifferli said. The smaller the particles, the larger the surface area is 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 said.

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

Of course, she also acknowledges that coating industrial-scale electrodes partly with gold can get expensive. But she said the energy  they can save and potential of reuse for such electrodes may balance the initial cost.

"It's a trade off," Hamad-Schifferli said. " Gold is obviously more expensive than copper. But if it helps you to get a product that's more attractive, like methane instead for carbon dioxide, in addition to a lower energy consumption, than 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."

This post was originally published on Smartplanet.com

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