new findings

Rice University and UH labs team up to improve emerging carbon capture technique

New research from Rice and UH has helped boost the lifespan of CO2RR systems, a newer technology used for carbon capture. Photo via htxenergytransition.org

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.”

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A View From HETI

A team from UH has published two breakthrough studies that could help cut costs and boost efficiency in carbon capture. Photo courtesy UH.

A team of researchers at the University of Houston has made two breakthroughs in addressing climate change and potentially reducing the cost of capturing harmful emissions from power plants.

Led by Professor Mim Rahimi at UH’s Cullen College of Engineering, the team released two significant publications that made significant strides relating to carbon capture processes. The first, published in Nature Communications, introduced a membraneless electrochemical process that cuts energy requirements and costs for amine-based carbon dioxide capture during the acid gas sweetening process. Another, featured on the cover of ES&T Engineering, demonstrated a vanadium redox flow system capable of both capturing carbon and storing renewable energy.

“These publications reflect our group’s commitment to fundamental electrochemical innovation and real-world applicability,” Rahimi said in a news release. “From membraneless systems to scalable flow systems, we’re charting pathways to decarbonize hard-to-abate sectors and support the transition to a low-carbon economy.”

According to the researchers, the “A Membraneless Electrochemically Mediated Amine Regeneration for Carbon Capture” research paper marked the beginning of the team’s first focus. The research examined the replacement of costly ion-exchange membranes with gas diffusion electrodes. They found that the membranes were the most expensive part of the system, and they were also a major cause of performance issues and high maintenance costs.

The researchers achieved more than 90 percent CO2 removal (nearly 50 percent more than traditional approaches) by engineering the gas diffusion electrodes. According to PhD student and co-author of the paper Ahmad Hassan, the capture costs approximately $70 per metric ton of CO2, which is competitive with other innovative scrubbing techniques.

“By removing the membrane and the associated hardware, we’ve streamlined the EMAR workflow and dramatically cut energy use,” Hassan said in the news release. “This opens the door to retrofitting existing industrial exhaust systems with a compact, low-cost carbon capture module.”

The second breakthrough, published by PhD student Mohsen Afshari, displayed a reversible flow battery architecture that absorbs CO2 during charging and releases it upon discharge. The results suggested that the technology could potentially provide carbon removal and grid balancing when used with intermittent renewables, such as solar or wind power.

“Integrating carbon capture directly into a redox flow battery lets us tackle two challenges in one device,” Afshari said in the release. “Our front-cover feature highlights its potential to smooth out renewable generation while sequestering CO2.”

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