Catalyst design speeds up CO2 conversion to carbon products

SOPHIA CHEN: The challenge for the world to reduce carbon emissions is steep. To reduce these emissions in the long run, some scientists believe it will be necessary to extract carbon dioxide from the air. But once you extract all that carbon dioxide, what do you do with it? Pelayo Garcia de Arquer, a materials scientist at the University of Toronto in Canada, has a potential answer. He’s working on technology for converting carbon dioxide into useful hydrocarbons, such as plastics, fabrics and fuels that are now produced by the petrochemical industry. In other words, he’s trying to turn lemons into lemonade. 

PELAYO GARCIA DE ARQUER: Our approach is to decarbonize this process by taking existing CO2 in the atmosphere, in the exhaust of an industry for example, and using electricity, which could come from renewables, and using water, and upgrade the CO2 into other molecules that can be used in these production systems, for example upgrading CO2 into ethylene, which is the precursor to a lot of polymers. 

SC: To convert carbon dioxide into ethylene, they pump CO2 gas to a spongelike catalyst interface, where the CO2 breaks down and ultimately reacts with water and an electrolyte. But it’s difficult to orchestrate this reaction quickly and efficiently, at the rates needed to make this technology economically viable. On their own, the individual reactants don’t tend to move to the right location very quickly. 

PGDA: You need to have all the ingredients of your cake in the right place and in the right time. 

SC: The difficulty is that CO2 does not like to dissolve in water. It also tends to undergo undesired reactions with the electrolyte to produce hydrogen molecules, for example. This makes the reactions proceed slowly. So their lab’s innovation was to include an extra ingredient on the surface of the catalyst known as an ionomer, a polymer that conducts ions. The ionomer had both hydrophobic and hydrophilic parts, which in effect created distinct channels for carbon dioxide, water, and the other ingredients to travel through separately to reach the catalyst. Monitoring the electric activity in their system, which is an indication of how quickly the chemical reaction is proceeding, they measured an electric current density of more than one ampere per square centimeter, which Garcia de Arquer says is about 10x improvement compared to the state-of-the-art just 2 years ago. 

PGDA: This is enabled, we believe, because of this phenomenon, like CO2 can travel faster through these more dry channels that do not have water.

SC: They also achieved an efficiency of 45%, meaning that 45% of the energy they put in created the ethylene. It’s not clear yet what metrics will make this system commercially viable, as the economics depend on many outside factors, such as the cost of electricity. But Garcia de Arquer says that the field is moving closer to a deployable technology.

PGDA: Achieving current densities in the realm of amperes per square centimeter, together with energy efficiencies above 60%, that’s the threshold we predict with the numbers we have right now, where we think things will become more and more interesting.