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Mainly due to the extensive use of fossil fuels, CO2<\/sub>\u00a0concentrations in the atmosphere have risen from 280 parts per million (ppm) in the pre-industrial era to today’s 410 ppm. With the ever-increasing share of polymer materials in the modern economy, addressing CO2<\/sub>\u00a0emissions associated with plastic production has become a strategic focal point.<\/p>\n\n\n\n Life-cycle analyses of fossil-based feedstocks for the petrochemical and chemical industries, such as ethylene, propylene, and others, show that their production emits approximately 0.4\u20131.2 kg of CO2<\/sub> per kg of feedstock produced by petrochemical cracking processes. Data like this has urged scientists to explore new carbon capture methods that can convert atmospheric CO2<\/sub> into chemicals traditionally sourced from oil or natural gas. Such a scheme, together with the use of recyclable feedstock, has the potential to circularize the polymer production chain.<\/p>\n\n\n\n Besides, electrochemical carbon capture offers an attractive opportunity to store renewable energy in a chemical form by producing carbon-based fuels and chemical feedstock from CO2<\/sub>. The electrochemical reduction of CO2<\/sub> is a complex conversion process comprising multiple proton-electron reaction steps, ultimately generating products with high commercial value, like ethylene, methane, or formic acid.<\/p>\n\n\n\n In the traditional fuel cell-based electrochemical reactor designs, electrodes are separated by a polymer membrane. Due to the low specific surface area, these designs possess intrinsic mass transfer limitations between gas-liquid-solid phases, limiting the overall conversion efficiency. To overcome these issues and enable highly efficient electrochemical CO2<\/sub> conversion, researchers have focused their attention on the development of porous gas diffusion metal electrocatalysts.<\/p>\n\n\n\n As one of the most critical components in a CO2<\/sub> conversion system, the gas diffusion catalytic electrodes have been the subject of intensive research in previous years. One of the most promising avenues to explore is enhancing the CO2<\/sub>selectivity of the catalyst\/electrode assembly. The use of CO2<\/sub> adsorbing materials as an electrode coating proved a promising approach to improve the selectivity of CO2<\/sub> conversion. Unfortunately, the design and synthesis of dedicated compounds with high selectivity and permeability for CO2<\/sub> are complex and expensive.Related: Planetary Hydrogen Ocean Air Capture: Capturing and Storing CO2 while Producing Hydrogen<\/a><\/em><\/p>\n\n\n\n Recently, a research group led by Dr. Yoshikazu Ito, an associate professor at the University of Tsukuba, demonstrated how an inexpensive polymer coating applied to a porous tin (Sn) electrocatalyst can increase CO2<\/sub> conversion efficiency several-fold. Their research was published in the journal ACS Catalysts<\/em><\/a> on July 26th<\/sup>, 2021. <\/p>\n\n\n\n Some polymers like polyethyleneimine (PEI) and polyethylene glycol (PEG) can effectively capture CO2<\/sub> molecules. The idea of Dr. Ito’s team was that such CO2<\/sub>-absorbing polymers could effectively increase the number of CO2<\/sub>molecules reaching the catalyst surface and create a CO2<\/sub>-rich local environment. The result will be an accelerated catalytic reaction on the catalyst’s surface.<\/p>\n\n\n\n The scientists developed an original deposition method that enabled them to create a special conformal PEG (a low-cost and abundant polymer with a wide range of applications) coating on a porous tin electrode without affecting the porosity of the electrocatalyst. The thickness of the polymer layers was optimized in a series of detailed investigations while monitoring the performance of the polymer-coated metal catalyst.<\/p>\n\n\n\n Conventionally, tin-based catalysts are used to convert CO2<\/sub> to formic acid or formate (HCOO\u2212<\/sup>). The experiments of Dr. Ito’s colleagues demonstrated that the PEG-coated electrocatalyst could produce 1.5 times more formate compared to a similar non-coated porous electrode. Compared to a conventional tin plate electrode, the formate production rate was 24 times higher, with no byproducts present (with 99% formate yield).<\/p>\n\n\n\n Next, the scientist devised a series of experiments to understand how the CO2<\/sub> molecules are transferred through the polymer coating and delivered to the catalytically active site. They have compared the CO2<\/sub> conversion rates of the PEG-coated catalyst and the same catalyst coated with another CO2<\/sub>-capturing polymer (PEI), which has a stronger affinity to CO2<\/sub>. The PEG-coating still outperformed the PEI-coating in terms of CO2<\/sub> conversion efficiency.<\/p>\n\n\n\n Further theoretical modeling revealed that PEI-coating held the CO2<\/sub> molecules too tightly, whereas PEG-coating provided the right balance between capture, transport, and release at the electrocatalyst surface. Another critical factor in that balance was the morphology of the polymer coating itself. The PEG-coating was too dense and thick, which also had a detrimental effect on CO2<\/sub> conversion.<\/p>\n\n\n\n According to the team, the newly-developed polymer coating can be employed to improve the existing electrosynthesis processes where an initial CO2<\/sub> adsorption step drives further electrochemical reactions. Such developments enable the production of many other valuable chemicals, such as methane, methanol, ethane, ethanol, and olefins, from atmospheric CO2<\/sub>.<\/p>\n\n\n\n Jeong, S., et al.<\/em>, (2021) Polyethylene Glycol Covered Sn Catalysts Accelerate the Formation Rate of Formate by Carbon Dioxide Reduction. ACS Catalysis 11<\/em> (15), 9962-9969. Available at: https:\/\/doi.org\/10.1021\/acscatal.1c02646<\/a> [Accessed on September 1st<\/sup> 2021].<\/p>\n\n\n\n University of Tsukuba (2021) Polymer coating accelerates fuel production<\/em> [Online] Science Daily. Available at: https:\/\/www.sciencedaily.com\/releases\/2021\/08\/210805133758.htm<\/a> [Accessed on September 1st<\/sup> 2021].<\/p>\n\n\n\n Adamu, A., et al.<\/em>, (2020) Process intensification technologies for CO2<\/sub> capture and conversion \u2013 a review. BMC Chem. Eng.<\/em> 2, 2. Available at: https:\/\/doi.org\/10.1186\/s42480-019-0026-4Y<\/a> [Accessed on September 1st<\/sup> 2021].<\/p>\n\n\n\n Pappijin, C. A. R, et al.<\/em>, (2020) Challenges and Opportunities of Carbon Capture and Utilization: Electrochemical Conversion of CO2<\/sub> to Ethylene. Front. Energy Res.<\/em> Available at: https:\/\/doi.org\/10.3389\/fenrg.2020.557466<\/a> [Accessed on September 1st<\/sup> 2021].<\/p>\n\n\n\nCO2<\/sub>\u00a0Conversion into Value-Added Chemicals<\/strong><\/h3>\n\n\n\n
What Are the Limitations for Electrochemical Carbon Capture?<\/strong><\/h3>\n\n\n\n
Polymer Coatings Accelerate Electrocatalysis<\/strong><\/h3>\n\n\n\n
Optimized Polymer-Coated Metal Catalyst for Future Clean Technology Applications<\/strong><\/h3>\n\n\n\n
References and Further Reading<\/strong><\/h3>\n\n\n\n
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