Using aluminum and oxygen, new technology can convert carbon dioxide into useful chemicals and also generate substantial amounts of electrical energy, researchers say.
The large-scale adoption of carbon capture, utilization and sequestration (CCUS) technologies is currently limited in part by how much energy it can take to capture carbon. In addition, methods to make the most of carbon dioxide once it gets stored by converting it into useful chemicals and fuels have proven difficult to develop.
But recently, chemical engineer Lynden Archer and his colleagues at Cornell University investigated whether electrochemical cells could both capture carbon dioxide and generate power. Such electrochemical cells, they hypothesized, would use a metal as the anode and mixed streams of carbon dioxide and oxygen as the active ingredients of the cathode. The electrochemical reactions between the anode and the cathode would sequester the carbon dioxide into carbon-rich compounds while also producing electricity.
Archer and his colleague Wajdi Al Sadat detailed their findings in the 20 July online edition of the journal Science Advances.
Previous research used lithium, sodium, and magnesium as the anodes in such electrochemical cells. These converted carbon dioxide into carbonates, “which are not that useful,” Archer says. “It then occurred to us to use aluminum, which is the third most abundant element in Earth's crust.” Aluminum's abundance makes it cheap, and it is also less chemically reactive than lithium and sodium, which makes it safer to work with, Archer adds.
In the new device, the anode consists of aluminum foil, the cathode consists of a porous, electrically conductive material such as a stainless steel mesh that allows carbon dioxide and oxygen to pass through it, and the electrolyte bridging the anode and cathode is a liquid through which molecules can diffuse.
In experiments, the electrochemical cell could generate as much as 13 ampere-hours for each gram of carbon it captured, without the need for a catalyst or high temperatures. Moreover, it converted carbon dioxide into aluminum oxalate, which, in turn, is easily converted into oxalic acid, a chemical widely used in industry. “It's a versatile product that's a nice starting material for plastics and so forth,” Archer says. In theory, adding extra compounds to the cathode might help convert carbon dioxide to other useful chemicals, Archer adds.
Archer notes that the electrolyte in his group’s electrochemical cell does not work if exposed to water. This is a problem because the carbon dioxide emissions that this device might treat, such as those from factories or power plants, might be loaded with moisture. However, it might be possible to find an electrolyte that is much less sensitive to water, Archer says.
Charles Q. Choi is a science reporter who contributes regularly to IEEE Spectrum. He has written for Scientific American, The New York Times, Wired, and Science, among others.