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Green Chemistry

Improved electrode efficiently converts CO2 to ethylene

Electrochemical system runs 15 times as long as best previous design

by Stu Borman
May 21, 2018 | APPEARED IN VOLUME 96, ISSUE 21

09621-scicon7-electrode.jpg
Credit: Adapted from Science
In the new electrode design, electrons and water molecules reach the Cu catalyst (red spheres) through layers of graphite (rods) and carbon nanoparticles (gray spheres), while CO2 accesses Cu via a porous polytetrafluoroethylene layer (gray cylinders). The catalyst electroreduces CO2 in the presence of H2O to form ethylene.

Researchers have been trying for some time to develop an efficient and stable industrial process in which renewable energy converts the greenhouse gas carbon dioxide to ethylene, a chemical feedstock for polyethylene production that usually has to be obtained from petroleum. Such a system could make it more feasible economically for industry to capture CO2 emissions, reducing pollution and producing a useful product at the same time. Edward H. Sargent of the University of Toronto and coworkers have now developed a system that moves this concept closer to reality (Science 2018, DOI: 10.1126/science.aas9100). As in earlier work, a copper catalyst in a gas diffusion electrode catalyzes reduction of gaseous CO2 in the presence of an aqueous hydroxide solution to produce ethylene. But the researchers’ use of a more highly concentrated hydroxide solution than before improved their system’s ethylene selectivity from 60% to 70%. And in their electrode design, they positioned the copper catalyst between a porous polytetrafluoroethylene support layer, which is highly stable under CO2 reduction conditions, and carbon nanoparticle and graphite layers, which protect the catalyst and deliver current to it. The electrode design improved continuous run time by a factor of 15 and enabled the reaction to run faster and at much lower applied electrochemical potential than before, factors that boost energy efficiency. Catalysis engineer Guido Mul of the University of Twente comments that the technology still has a long way to go but that the new system’s productivity begins to approach levels that could be useful industrially.

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