Membraneless process and flow battery promise cheaper, greener carbon capture

Sometimes less really is more—at least that is the case when it comes to improving carbon capture systems, according to a team of researchers at the University of Houston.

Led by Mim Rahimi, a professor at UH’s Cullen College of Engineering, the team made two significant breakthroughs that could reduce the cost of capturing harmful emissions from power plants, marking a major step in addressing climate change.

The first method, published in Nature Communications, introduces a membraneless electrochemical process that slashes energy requirements for amine-based carbon dioxide (CO₂) capture. The second, featured on the cover of ACS ES&T Engineering, demonstrates a vanadium redox flow system capable of both capturing carbon and storing renewable energy.

“Climate change mitigation was basically the reason we pursued this research,” Rahimi said. “We need solutions, and we wanted to be part of the solution. The biggest suspect out there is CO₂ emissions, so the low-hanging fruit would be to eliminate those emissions.”

In the first research paper titled “A Membraneless Electrochemically Mediated Amine Regeneration for Carbon Capture,” the team first focused on replacing the conventional ion-exchange membrane in the electrochemically mediated amine regeneration process with gas diffusion electrodes.

That proved to be a game-changer. Not only were the membranes the most expensive part of the system, but they were also a primary reason for performance issues and maintenance cost.

By engineering the gas diffusion electrodes, the team was able to achieve more than 90% CO₂ removal, nearly 50% more than traditional EMAR approaches. That’s a capture cost of approximately $70 per metric ton of CO₂, which makes it competitive with state-of-the-art amine scrubbing methods, according to Ph.D. student Ahmad Hassan.

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

Fellow Ph.D. student Mohsen Afshari built on those advances, publishing his findings in the second paper, “A Vanadium Redox Flow Process for Carbon Capture and Energy Storage.” That paper presented a reversible flow battery architecture that absorbs CO₂ during charging and releases it upon discharge.

By leveraging the vanadium’s chemistry, the process displayed strong cycle stability and a high capture capacity, suggesting the technology could provide carbon removal and grid balancing when paired with intermittent renewables.

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

These discoveries promise to make waves for carbon capture technology and the energy industry going forward, with the ultimate goal being to reduce the carbon footprint associated with everyone.

“These publications reflect our group’s commitment to fundamental electrochemical innovation and real-world applicability,” Rahimi said. “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.”