Researchers from the University of Tsukuba (Tsukuba, Japan) and Osaka University (Suita, Japan) designed a polymer-coated metal catalyst that accelerates carbon dioxide (CO2) transformation into a useful carbon-based fuel. In their study, which was recently published in ACS Catalysis, the researchers illustrate how porous tin (Sn) catalysts coated with polyethylene glycol (PEG) facilitates CO2 transformation into this useful, eco-friendly fuel source.
Various polymers can capture CO2 molecules, and Sn catalysts are known to reduce CO2 to other molecules like formate (HCOO-), which can be reused to power fuel cells.
“We were interested in combining these capabilities into a single catalytic system that could scrub CO2 from its surroundings and recycle it into formate,” says research group leader Prof. Yoshikazu Ito. “However, it's difficult to obtain only the desired product, formate, at a high production rate and in high yield, so we had to fine-tune the catalyst design.”
The HCOO- production rate of PEG-coated Sn was 24 times higher than that of a conventional Sn plate electrode, and no byproducts were detected. To understand this enhanced CO2-reduction reaction, the researchers fabricated an Sn catalyst coated with another CO2-capturing polymer, polyethyleneimine (PEI), whose structure interacts differently with incoming CO2.
The PEG-coated Sn still outperformed the PEI-coated Sn, and considering the chemical characteristics of these polymers, the authors proposed that PEI held the CO2 molecules too tightly, whereas PEG struck a key balance in capturing and then releasing CO2 to the catalytic Sn core.
“Modeling this reaction using theoretical computations confirmed the favorability of PEG shuttling CO2 to the Sn center and explained the accelerated formate production,” explains PhD student Samuel Jeong. “However, we wanted to further clarify the PEG-CO2 interactions.”
More detailed computations revealed that while the absence of polymer limits the Sn catalyst's CO2-capture ability, an excessively dense layer of PEG inhibits CO2 transfer to the metal surface, thereby decreasing HCOO- production. Therefore, a complete but relatively sparse layer of PEG is optimal for funneling CO2 to Sn, while maintaining a CO2-rich environment and preventing byproduct release. It also means that this technique can be used to develop systems that efficiently recycle CO2 into useful compounds that can power fuel cell devices that provide green electricity, according to the researchers.
Source: University of Tsukuba, www.tsukuba.ac.jp.