A team of researchers led by professors from two Houston universities has discovered new methods that help stabilize an emerging technique known as carbon dioxide reduction reaction, or CO2RR, that is used for carbon capture and utilization processes.
The team led by Rice University’s Haotian Wang, associate professor in chemical and biomolecular engineering, and Xiaonan Shan, associate professor of electrical and computer engineering at University of Houston, published its findings in a recent edition of the journal Nature Energy.
CO2RR is an emerging carbon capture and utilization technique where electricity and chemical catalysts are used to convert carbon dioxide gas into carbon-containing compounds like alcohols, ethylene, formic acids or carbon monoxide, according to a news release from Rice. The result can be used as fuels, chemicals or as starting materials to produce other compounds.
The technology is used in commercial membrane electrode assembly (MEA) electrolyzers to convert carbon dioxide into valuable compounds, but the technology isn’t perfected. A significant challenge in CO2RR technology has been the accumulation of bicarbonate salt crystals on the backside of the cathode gas diffusion electrode and within the gas flow channels. The salt precipitates block the flow of carbon dioxide gas through the cathode chamber, which reduce the performance and can cause a failure of the electrolyzers.
The goal in the study was to understand why and how bicarbonate salts form during this reaction. The Rice and UH teams worked together using operando Raman spectroscopy, which is a technique that allows researchers to study the structure of materials and any precipitates that adhere to them while the device is functioning.
“By utilizing operando Raman spectroscopy and optical microscopy, we successfully tracked the movement of bicarbonate-containing droplets and identified their migration pattern,” Shan said in the release. “This provided us the information to develop an effective strategy to manage these droplets without interrupting system stability.”
Next, the team worked to prevent the salt crystals from forming. First, they tested lowering the concentration of cations, like sodium or potassium, in the electrolyte to slow down the salt formation. This method proved to be effective.
They also coated the cathode with parylene, a synthetic polymer that repels water, like Teflon, which also notably improved the stability of the electrolyzer and prevented salt accumulation.
“Inspired by the waxy surface of the lotus leaf which causes water droplets to bead up and roll off, carrying off any dirt particles with it and leaving the leaf’s surface clean, we wondered if coating the gas flow channel with a nonstick substance will prevent salt-laden droplets from staying on the surface of the electrodes for too long and, therefore, reduce salt buildup.” Wang said in the release.
According to Wang, these relatively simple discoveries can extend the operational lifespan of CO2RR systems from a few hundred hours to over 1,000 hours.
The findings also have major implications for commercial applications, Shan added.
“This advancement paves the way for longer-lasting and more reliable (CO2RR) systems, making the technology more practical for large-scale chemical manufacturing,” Shan said in the release. “The improvements we developed are crucial for transitioning CO2 electrolysis from laboratory setups to commercial applications for producing sustainable fuels and chemicals.”
