Foam Fosters Carbon Dioxide Conversion

A foam of copper offers sponge-like pores and channels, providing more active sites for CO2 reactions than a simple surface.
Source: Palmore lab/Brown University

This could result in “the use of renewable energy to drive the electrochemical reduction of CO₂ to chemical feedstock such as formic acid, CO, ethylene, etc., which is the focus of our research center,” says Tayhas Palmore, professor of engineering at the school.“Copper has been studied for a long time as an electrocatalyst for CO₂ reduction, and it’s the only metal shown to be able to reduce CO₂ to useful hydrocarbons,” explains Palmore. “There was some indication that if you roughen the surface of planar copper, it would create more active sites for reactions with CO₂.”Palmore’s team found that copper foam, made by depositing copper on a surface in the presence of hydrogen and a strong electric current, has such a rough surface, with sponge-like pores and channels of varying sizes.The researchers tested the copper foams, deposited on an electrode, in an electrochemical reaction with CO₂ in water to see what products could be produced. The copper foam converted the CO₂ into formic acid — a compound often used as a feedstock for microbes that produce biofuels — at a much greater efficiency than planar copper, and small amounts of propylene — a first in reactions involving copper. More details appear in a recent issue of the journal ACS Catalysis.“The product distribution was unique and very different from what had been reported with planar electrodes, which was a surprise,” notes Palmore. “We’ve identified another parameter to consider in the electroreduction of CO₂. It’s not just the kind of metal that’s responsible for the direction this chemistry goes, but also the architecture of the catalyst.”The team’s ongoing studies include focus on how changes in pore diameter, pore depth and electrolyte concentration affect products obtained. But Palmore’s ultimate goal, which she views as a key challenge, is to identify “structures that yield high faradaic efficiencies for a single reduction product.”“We are interested in the more fundamental question, which is ‘how does 3D structure affect product distribution?’ We would be delighted if the studies led us to structures that yielded more of or exclusively one product, be it formic acid or other reduction products.”     Palmore expects to be able to report results of these studies within 6–12 months. The team has not performed any mechanical tests to determine the nanofoam catalyst’s robustness, but Palmore says the foams seem to be stable during electrolysis (i.e., no indication of loss of mass). In addition, she believes the copper foam’s susceptibility to poisoning equals that of conventional copper electrodes. Palmore feels producing the nanofoam catalysts on electrodes large enough for pilot-plant studies is achievable. “These are electrodeposited foams, so scale is only dependent on the size of the electrochemical cell (of which industry already has very large versions of) or the method used for electrodeposition.”However, “We would need an industrial partner to perform a pilot-plant study as we don't have that capability in an academic laboratory,” she adds.Palmore says companies have been in contact about cooperating on the further development of the catalyst, and she welcomes new industry affiliates.