With these scalable, affordable materials, carbon capture can become practical

Northwestern University researchers have demonstrated that there are a variety of suitable and abundant materials that can promote the potential of direct capture of carbon capture technology that pulls carbon dioxide directly from the air.

In a paper published in the journal Environmental Science and Technology, researchers proposed new low-cost materials to facilitate moisture rotation to capture and then release carbon dioxide based on the moisture content of local air, calling it “one of the most promising methods for carbon dioxide capture.”

The carbon dioxide in the atmosphere continues to increase, and despite efforts around the world to reduce carbon waste, it is expected to increase in the coming decades. Efficient and economical ideas of exploring how to isolate excess CO2 from the air can help make up for the ground by offsetting emissions from delocalized sectors such as delocalized and agriculture, where emissions are particularly difficult to determine and capture.

Humid direct air capture (DAC) uses changes in humidity to capture carbon, which will be central to a global strategy to combat climate change, but its scalability is limited due to the previously ubiquitous use of engineered polymer materials, called ion exchange resins. The team found that they could reduce costs and energy utilization by adopting sustainable, rich and inexpensive materials, which can often be supplied from organic waste or raw materials, making DAC technology cheaper and more scalable.

“This study introduces and compares novel platform nanomaterials for moisture volatile carbon capture, especially carbonaceous materials such as activated carbon, nanostructured graphite, carbon nanotubes and flake graphite as well as metal oxide nanoparticles, including iron, aluminum and manganese oxides,” said Northwestern Materials Science and Machine Science ph.d. Candidate John Hegarty, co-author. “For the first time, we applied a structured experimental framework to identify the important potential of different materials for CO2 capture. Among these materials, alumina and activated carbon have the fastest kinetics, while iron oxide and nanostructured graphite can capture the most CO2.”

The paper demonstrates that the pore size of a material (the space pocket in the porous material where carbon dioxide can nest) is of great significance in predicting the power it captures carbon. Engineers believe that such research will support the development of design principles to improve performance by modifying the structure of the material.

Scaling carbon capture

Due to its high cost and technical complexity, traditional methods of directly capturing atmospheric carbon dioxide cannot compete in many markets. More accessible and low-cost DAC technology can offset emissions from agriculture, aviation and concrete and steel manufacturing sectors that are challenging or impossible to decarbonize through renewable energy alone.

“The moisture volatile approach can isolate carbon dioxide at low humidity and release it at high humidity, reducing or eliminating the energy costs associated with heating adsorbent materials, so it can be reused,” said McCormick School of Engineering. According to Shindel and other authors of the study, this approach is attractive because it removes carbon from almost anywhere and can be used to connect with other systems that will run in the carbon utilization paradigm.

“If you design the system correctly, you can rely on natural gradients, for example, through day and night cycles, or using two rolls of air, one of which is wet and is already dry in the region,” said Professor Vinayak P. Dravid, a materials engineer, who led the study.

After the team evaluated why ion exchange resins were so effective in promoting capture, the ideal pore size and the presence of negatively charged ions on their surface combined with the carbon dioxide that could be attached to – they identified other platforms with more abundant and similar properties, with the emphasis on not adding materials in the environment.

Previous literature tends to wrap the mechanisms of the entire system together, so it is difficult to evaluate the performance impact of a single component. By systematically, especially looking at each material, they found the “just right” mid-range of the pore size (about 50 to 150 Estrom) with the highest swing ability, finding correlations between the amount of area in the pore and the capacity shown by the material, Hegarty said.

The team plans to improve their understanding of the life cycle of new materials, including the overall cost and energy use of the platform, and hopefully it inspires other researchers to think out of the box.

“As a field, carbon capture is still in its nascent stage,” said Shindel. “This technology will only become cheaper and more efficient until it becomes a viable way to meet global emissions. We hope to see these materials tested at scale in the pilot study.”

About the researchers

Dravid is a professor of materials science and engineering at Abraham Harris of McCormick and a faculty member of the Paula M. Trienens Institute for Sustainability and Energy. He is also the founding director of the Center for Atomic and Nanoscale Features (NUANCE) at Northwestern University, and the Soft Nanotech Experimental (Shyne) Resources, and serves as Deputy Director of Global Programs at the School of Nanotechnology International. Hegarty and Shindel share the first author, as well as a PhD from the Weinberg School of Arts and Sciences. Student Michael L. Barsoum and his consultant, Northwestern Chemistry Chairman and Professor Omar K. Farha are also authors.