New materials split between water and carbon dioxide

Researchers from North Carolina State University have significantly boosted the efficiency of two related chemical techniques: splitting water to create hydrogen gas and splitting carbon dioxide (CO₂) to create carbon monoxide (CO). The products created by these techniques are valuable feedstocks for clean energy and chemical manufacturing applications.

The water-splitting process, reported in a paper in Science Advances, successfully converts 90% of water into hydrogen gas, while the CO₂-splitting process, reported in a paper in ChemSusChem, converts more than 98% of CO₂ into CO. In addition, the process also uses the released oxygen to convert methane into syngas, which can be used as a feedstock for fuels and other products.

"These advances are made possible by materials that we specifically designed to have the desired thermodynamic properties for each process," says Fanxing Li, an associate professor of chemical and biomolecular engineering at NC State who is corresponding author of the two papers on the work. "These properties had not been reported before unless you used rare earth materials."

For the CO₂-splitting process, the researchers developed a nanocomposite of strontium ferrite dispersed in a chemically inert matrix of calcium oxide or manganese oxide. As CO₂ passes over a packed bed of particles composed of the nanocomposite, they split the CO₂ and capture one of its oxygen atoms, reducing the CO₂ to CO.

"We think both of these materials and processes represent significant steps forward. They use relatively inexpensive materials to efficiently extract valuable feedstock from resources that are either readily available (in the case of water) or are actually greenhouse gases (in the cases of CO2 and methane)."Fanxing Li, North Carolina State University

"Previous CO₂ conversion techniques have not been very efficient, converting well below 90% of the CO₂ into CO," Li says. "We reached conversion rates as high as 99%. And CO is valuable because it can be used to make a variety of chemical products, including everything from polymers to acetic acid." The oxygen captured during the CO₂-splitting process can be combined with methane and converted into syngas using solar energy.

For the water-splitting process, the researchers created iron-doped barium manganese oxide particles. Other than the difference in materials, the process is remarkably similar. As water – in the form of steam – is run over a bed of the particles, the iron-doped barium manganese oxide splits the water molecules and captures the oxygen atoms to leave behind pure hydrogen gas.

"Our conversion here is 90%, which compares very favorably to other techniques – which are often in the 10–20% range," says Vasudev Haribal, a PhD student at NC State and lead author of the paper on the water-splitting work. The oxygen captured during the water-splitting process can also be used to make syngas, using the same technique employed with the CO₂-splitting process.

"We think both of these materials and processes represent significant steps forward," Li says. "They use relatively inexpensive materials to efficiently extract valuable feedstock from resources that are either readily available (in the case of water) or are actually greenhouse gases (in the cases of CO₂ and methane).

"We are now working on developing materials that are even more efficient. And we're open to working with outside groups who are interested in scaling these processes up for manufacturing."

This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.