Scientists Develop Polymer-Coated Metal Catalyst to Efficiently Recycle CO2

The accumulation of greenhouse gases, such as carbon dioxide (CO₂), in the atmosphere contributes to climate change. Therefore, capturing and recycling CO₂ are crucial for reducing detrimental environmental effects and to deal with the climate crisis.

Japanese scientists created a polymer-coated metal catalyst that speeds up CO₂ conversion and provides green energy insights.

Scientists from the University of Tsukuba showed how porous tin (Sn) catalysts coated with polyethylene glycol (PEG) polymer promote CO₂ transformation into a useful carbon-based fuel. The research has been published in the ACS Catalysis journal.

Different polymers can capture CO₂ molecules, and Sn catalysts are recognized for reducing CO₂ to other molecules, such as 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. 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.

Yoshikazu Ito, Professor and Research Group Leader, University of Tsukuba

The production rate of formate by PEG-coated Sn was found to be 24 times higher when compared to conventional Sn plate electrodes, and no byproducts were identified (>99% yield of formate). To gain in-depth knowledge on this enhanced CO₂-reduction reaction, the scientists created an Sn catalyst coated with another CO₂-capturing polymer (polyethyleneimine; PEI) whose structure interacts variably with incoming CO₂.

The PEG-coated Sn still outclassed the PEI-coated Sn, and the researchers took the chemical characteristics of these polymers into account and remarked that PEI held the CO₂ molecules too tightly. On the contrary, 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. However, we wanted to further clarify the PEG-CO₂ interactions.

Samuel Jeong, PhD Student, University of Tsukuba

Further comprehensive computations showed that the absence of polymer restricts the Sn catalyst’s ability to capture CO₂ and that an excessively dense layer of PEG inhibits the transfer of CO₂ to the metal surface, which decreases formate production. Hence, a complete but relatively minimal layer of PEG is ideal for funneling CO₂ to Sn, while maintaining a CO₂-rich environment and prohibiting byproduct release.

The mantra “reduce, reuse, recycle” does not refer to single-use plastics any longer. The simple catalyst-coating technique indicated by Ito and colleagues can be employed to create systems that effectively recycle CO₂ into beneficial compounds, such as formate, which can power fuel cell devices that offer green electricity.

Journal Reference:

Jeong, S., et al. (2021) Polyethylene Glycol Covered Sn Catalysts Accelerate the Formation Rate of Formate by Carbon Dioxide Reduction. ACS Catalysis. doi.org/10.1021/acscatal.1c02646.