How NAU faculty are advancing technology to remove greenhouse gas from the air 

A graphic showing how moisture-based direct air capture works.

How do we remove greenhouse gases from the air? 

Answering that question is a critical step in slowing the devastating effects of global climate change. A mechanical engineer from NAU is on the front lines of creating a machine that will, in a way, vacuum out greenhouse gases and create a cleaner atmosphere. 

Jennifer Wade is leading two separate but related projects, funded by the National Science Foundation and Department of Energy (DOE), related to direct air capture, which is the process of separating carbon dioxide—the most abundant greenhouse gas (GHG)—out of the atmosphere and storing it permanently and safely, all without using the fossil fuels that would contribute additional CO2 into the air. The U.S. government is prioritizing direct air capture in response to scientific findings that the world is on a collision course with uncontrolled warming unless countries make drastic and immediate changes, both to stop further GHG emissions and remove unavoidable GHG from the air. 

In fact, it’s critical enough that U.S. leaders have set the Carbon Negative Earthshot: Being able to remove carbon at $100 a ton at a scale of a million tons per year. Currently, Wade estimates that first-of-kind attempts of direct air capture and storage are in the range of $300-to-$400 a ton. It’s a long shot, Wade said, but it is doable. 

“All of those climate models show that we have to turn off emissions as fast as we can but stopping the greenhouse gas emission is not enough to stay below uncontrolled warming,” she said. “We also have to just get it out of the atmosphere, so we need all the things to limit warming, including carbon dioxide removal.” 

Direct air capture, which is one type of carbon dioxide removal, removes CO2, the most abundant greenhouse gas, straight from the atmosphere. What that looks like isn’t a vacuum—more of a giant fan blowing air through “sticky” material to which mostly carbon dioxide adheres. The big questions are how to cost effectively scale these sticky material, how to efficiently release the COfrom the material and how to store the carbon dioxide once it’s concentrated—and how to do all of that quickly, effectively and with the fewest possible natural and financial resources. 

It’s an important piece of the climate puzzle, though not the only piece, Wade said; societies need to create smarter cities, transit and revamp our energy sector so we are burning less fossil fuel, and in climates where it makes sense, plant more trees and protect the ones we have. But that is not enough. Society needs to be tackling climate change with every tool available and creating new tools along the way. 

“The thing I tell people is that I want this to work so we’re not instead injecting aerosols into our atmosphere to cool things down because we have no other choice,” she said. “Direct air capture is reversing the cause of the problem, not managing the symptom.” 

Jennifer Wade's lab group in the forestNSF grant: Mixing materials science and community engagement 

This $1.7 million, four-year grant is building on the research that is driving the few early commercial applications of direct air capture. Most materials that can separate carbon dioxide from the air require heat to re-release the gas to concentrate it for permanent storage. High temperature heat largely comes from fossil fuel combustion, but new solid sorbents can release the  CO2 at lower temperatures. Other investigators are looking at alternative energetic inputs that can more efficiently and quickly concentrate the trapped carbon.   

However, Wade’s collaborators at Arizona State University discovered a material that can release carbon using water instead of heat. But there are still questions before this family of materials can be commercialized: researchers don’t completely understand why this material responds to moisture, and they need to find a way to remain efficient with that water, and if possible, reclaim and reuse it. 

The NSF grant will allow Wade to examine new processes enabled by this new class of materials and couple them to other processes that can convert the carbon dioxide into a useful, non-fossil chemical. She also will look into technology that will allow them to use low-quality water, like saline aquifers or seawater. 

“We definitely don’t want to be competing with freshwater supplies,” she said. “We don’t want to solve one problem and create another.” 

Direct air capture systems will require land to contact the separators, and land to site new renewable power to operate these systems. In the Southwest and particularly in Arizona, much of the open lands are owned by sovereign Native nations. The researchers will work with Native nations, including communicating the motivation of the work, discussing various costs and how they plan to reduce those costs and collaborate on how to use the captured carbon, which can have real financial value. A company Wade is working with, for example, uses captured carbon dioxide to make ethanol and jet fuel.    

“We want the tribal communities to weigh in on whether that captured carbon is of any value, and if so, in what form do they want that captured carbon to be? Do they want us to trap it permanently or turn it into a commodity?” Wade said.  

Alternatively, they can look at the different types of inputs and optimize them on something that the tribal communities will value, such as treating the water used in the direct air capture process so it can be reused for agriculture. 

“As we optimize these processes, we want to weigh their objectives based on their input,” she said. “If possible, we want to scale the process to something that they could own and operate, as opposed to a giant oil company owning and operating it.” 

Lab members talk to community members at a festival.DOE grant: Finding the right questions to ask 

This $4.4 million, three-year grant is part of a $450 million expenditure from DOE, all aimed at the goal of developing clean energy technology and low-carbon manufacturing. NAU’s piece is a wide-ranging examination of the materials used to pull carbon out of the air—why does this process happen, how fast can it happen and how can the materials be manufactured and put to use to make direct air capture a reality. 

Nine investigators, including three from NAU, are looking into different pieces of this puzzle. They’re not testing any specific process or any kind of form for the carbon capture material; they’re just asking a lot of questions and going where the science takes them. 

“We’re just trying to understand the underlying phenomenon,” Wade said. “It’s largely still a mystery of what’s going on with these moisture-responsive materials.” 

This project is looking at a number of different pieces of the direct air capture process and how they may work together to make the whole process more efficient. In addition to Wade, mechanical engineering professor Heidi Feigenbaum will model structural mechanics of the materials, looking at how they strain and eventually fail when undergoing cycles of loading and unloading, and Miguel José Yacamán, Regents’ professor of applied physics and materials science, will look at the material microstructure in their native “wet” state and test how they change when temperature or moisture level changes. 

The anticipated results should help researchers make better materials—either materials that capture more carbon, that release that carbon more easily, that last significantly longer, that are less resource-heavy to create or any combination of the above. All of that will move the U.S. closer to its 2030 carbon capture goal. 

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Heidi Toth | NAU Communications
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NAU Communications