The electrochemical device captures carbon dioxide with the flick of a switch

(Nanowerk NewsThe new technology developed by Rice University engineers can lower the cost of capturing carbon dioxide from all types of emissions, a potential game changer for both industries seeking to adapt to evolving greenhouse gas standards and the emerging energy transition economies.

According to a study published in Natural (“Continuous carbon capture in a solid-electrolyte electrochemical reactor”), a system from chemical and biomolecular engineer Haotian Wang’s lab can directly remove carbon dioxide from sources ranging from exhaust gases to the atmosphere by using electricity to induce an electrochemical reaction based on water and oxygen. This technological feat could turn an immediate aerial capture of a fringe industry ⎯ there are only 18 factories currently operating worldwide ⎯ into a promising front for climate change mitigation.

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Most carbon capture systems involve a two-step process: First, a high pH liquid is used to separate carbon dioxide, which is acidic, from a mixed gas stream such as flue gas. Next, carbon dioxide is regenerated from solution by heating or by injecting a low pH liquid.

“Once the carbon dioxide is trapped in this solvent, you have to regenerate it,” Wang said.

“The traditional amine scrubbing method requires temperatures of 100-200 degrees Celsius (212-392 Fahrenheit). For a calcium carbonate based process, you need temperatures as high as 900 Celsius (1652 Fahrenheit).

“Literally no chemicals are produced or consumed with our process. We also don’t need to heat or stress our device, we just need to plug it into a power outlet and it will work.

Another drawback of current carbon capture technologies is their reliance on large-scale, centralized infrastructure. In contrast, the system developed in Wang’s lab is a scalable, modular, point-of-use concept that can adapt to various scenarios.

“This technology can be scaled to industrial settings ⎯ power plants, chemical plants ⎯ but the great thing is that it allows for small-scale use as well: I can even use it in my office,” said Wang. “We could, for example, pull carbon dioxide from the atmosphere and continuously inject this concentrated gas into a greenhouse to stimulate plant growth. We have heard from space technology companies that are interested in using devices on the space station to remove carbon dioxide exhaled by astronauts.”

The reactor developed by Wang and his team can continuously remove carbon dioxide from the simulated exhaust gas with an efficiency above 98% using relatively low electrical input.

“Electricity used to power a 50-watt light bulb for one hour will produce 10 to 25 liters of high-purity carbon dioxide,” said Peng Zhu, a chemical and biomolecular engineering graduate student and lead author of the study.

Wang noted that the process has “no carbon footprint or a very limited footprint” when powered by electricity from a renewable source such as the sun or wind.

“This is great news considering that renewable electricity is becoming more and more cost-effective,” said Wang.

The reactor consists of a cathode prepared to carry out oxygen reduction, an anode which carries out the oxygen evolution reaction, and a dense but porous solid electrolyte layer which allows efficient ion conduction. Earlier versions of the reactor were used to reduce carbon dioxide to pure liquid fuel and to reduce oxygen to pure hydrogen peroxide solution.

“Before, our group focused mainly on carbon dioxide utilization,” said Zhu. “We are working towards producing pure liquid products such as acetic acid, formic acid, etc.”

According to Wang, Zhu observed during the research process that gas bubbles flowed out of the reactor center chamber along with the liquid.

“At first, we didn’t pay much attention to this phenomenon,” Wang said. “However, Peng observed that if we apply more current, there will be more bubbles. It is a direct correlation, meaning something that is not random is happening.”

The researchers realized that the alkaline interface generated during the reduction reaction on the cathode side of the reactor interacts with carbon dioxide molecules to form carbonate ions. Carbonate ions migrate to the reactor’s solid electrolyte coating where they combine with protons generated from the oxidation of water on the anode side, forming a continuous stream of high-purity carbon dioxide.

“We randomly encountered this phenomenon during our previous studies,” said Wang. “We then tune and optimize the technology for these new projects and applications. We have spent many years working continuously on this type of electrochemical device.

“Scientific discoveries often require patience, constant observation, and curiosity to learn what is really going on, a choice not to ignore phenomena that do not always fit within the experimental framework.”