Researchers have discovered that a chemical element shows a “Goldilocks” degree of reactivity—neither too much nor too little—making it an excellent choice for carbon cleansing tools.
Vanadium, one of the CO2 capture materials, displaying a brilliant deep purple color. Image Credit: May Nyman, chemistry professor, OSU College of Science
The element is vanadium, and researchers at Oregon State University have shown that vanadium peroxide molecules can interact with and bind carbon dioxide, paving the way for enhanced carbon dioxide removal technology.
The study is part of a $24 million federal initiative to discover novel ways for direct air capture, or DAC, of carbon dioxide, a greenhouse gas produced by the combustion of fossil fuels and linked to climate change.
Facilities that filter carbon from the air have begun to sprout up throughout the world, although they are still in their infancy. Carbon dioxide mitigation technologies, such as those used in power plants, are becoming increasingly advanced. Scientists predict that both methods of carbon capture will be required if the Earth is to escape the worst effects of climate change.
May Nyman, the Terence Bradshaw Chemistry Professor in the College of Science at Oregon State, was selected to oversee one of the Department of Energy’s nine direct air capture projects in 2021. Her group is studying the process by which some transition metal complexes react with air to extract carbon dioxide and transform it into a metal carbonate, which is akin to the carbonate found in a variety of naturally occurring minerals.
The shift of electrons from low energy to high energy states and back again, giving birth to different hues, is the reason behind the moniker “transition metals,” which are found close to the center of the periodic table. The Scandinavian goddess of love, Vanadis, was named after her in old Norse mythology and is claimed to have been so beautiful that her tears changed to gold. This led scientists to choose vanadium for their study.
According to Nyman, the density of carbon dioxide in the atmosphere is 400 parts per million. This indicates that 400 air molecules, or 0.04%, are carbon dioxide for every million air molecules.
A challenge with direct air capture is finding molecules or materials that are selective enough, or other reactions with more abundant air molecules, such as reactions with water, will outcompete the reaction with CO2. Our team synthesized a series of molecules that contain three parts that are important in removing carbon dioxide from the atmosphere, and they work together.
May Nyman, Terence Bradshaw Chemistry Professor, College of Science, Oregon State University
One component was vanadium, which gets its name from the variety of exquisite colors it can display. The other component was peroxide, which joined with the vanadium to form a bond. According to Nyman, a vanadium peroxide molecule requires alkali cations for charge balancing since it is negatively charged. For this investigation, the researchers employed potassium, rubidium, and cesium alkali cations.
She continued by saying that the collaborators also experimented with replacing vanadium with other metals from the same neighborhood on the periodic table.
Nyman added, “Tungsten, niobium and tantalum were not as effective in this chemical form. On the other hand, molybdenum was so reactive it exploded sometimes.”
Furthermore, the researchers replaced the alkalis with ammonium and tetramethyl ammonium, the former of which has a mild acidity. The fact that certain chemicals had no reaction at all is a mystery that the researchers continue to investigate.
“And when we removed the peroxide, again, not so much reactivity. In this sense, vanadium peroxide is a beautiful, purple Goldilocks that becomes golden when exposed to air and binds a carbon dioxide molecule,” Nyman further added.
She points out that one other important property of vanadium is that it permits the absorbed oxygen to be released at a very low temperature—roughly 200 degrees Celsius.
She stated, “That’s compared to almost 700 degrees Celsius when it is bonded to potassium, lithium or sodium, other metals used for carbon capture. Being able to rerelease the captured CO2 enables reuse of the carbon capture materials, and the lower the temperature required for doing that, the less energy that’s needed and the smaller the cost. There are some very clever ideas about reuse of captured carbon already being implemented – for example, piping the captured CO2 into a greenhouse to grow plants.”
Tim Zuehlsdorff, an assistant professor of theoretical and physical chemistry at Oregon State, and Eduard Garrido, a postdoctoral researcher, were among the other authors of the study.
Nyman concluded, “I am also really proud of the hard work of the graduate students in my lab, Zhiwei Mao and Karlie Bach, and undergraduate Taylor Linsday. This is a brand new area for my lab, as well as for Tim Zuehlsdorff, who supervised PhD. student Jacob Hirschi on the computational studies to explain the reaction mechanisms. Starting a new area of study involves many unknowns.”
The study was conducted by Casey Simons of the University of Oregon and Eric Walter of the Pacific Northwest National Laboratory. The results were published in Chemical Science, the official journal of the Royal Society of Chemistry.
Journal Reference
Ribo, E. G., et. al. (2024) Implementing vanadium peroxides as direct air carbon capture materials. Chemical Science. doi:10.1039/D3SC05381D