Every year, the billions of metric tons of carbon dioxide (CO2) we release into the atmosphere add to the growing threat of climate change. But what if we could simply recycle all that wasted CO2 and turn it into something useful?
By adding electricity, water, and a variety of catalysts, scientists can reduce CO2 into short molecules such as carbon monoxide and methane, which they can then combine to form more complex hydrocarbon fuels like butane. Now, researchers think we could be on the cusp of a CO2-recycling revolution, which would capture CO2 from power plants—and maybe even directly from the atmosphere—and convert it into these fuels at scale, they report today in Joule.
Science talked with one of the study’s authors, materials scientists and graduate student Phil De Luna at the University of Toronto in Canada, about how CO2 recycling works—and what the future holds for these technologies. This interview has been edited for clarity and length.
Q: Why CO2 recycling?
A: The developed world has been emitting CO2 almost frivolously for a really long time, and there’s a lot that can be done there. But I could imagine a day when the entire energy mix is fueled by renewable energy sources, and then all of the hydrocarbon products—consumable plastics, the fuels that you need for long-term energy storage and heating your home in the winter—all of that could be derived from CO2 conversion. And then when that happens, CO2 becomes a way to store renewable energy, in chemical form, over long periods of time, in a stable way. And that’s kind of the goal—to have CO2 be a carrier of energy rather than just being a waste or an emission.
Q: Where did the idea come from?
A: The idea stems from artificial photosynthesis: Whereas nature has been able to take light, CO2, and water and create food, we’re looking at ways of engineering devices to take CO2, renewable energy, and water, and reduce that into more value-added products.
Q: How does this technology convert CO2 into fuel?
A: [It’s] kind of like a reverse fuel cell. There’s a cathode and an anode; at the anode, water is split into protons and oxygen gas, and at the cathode, CO2 is electrochemically reduced to other value-added chemicals, such as carbon monoxide, methane, ethylene. So you are feeding CO2 protons and electrons [from the water and the electricity], and you are electrochemically reducing them.
Q: It sounds like you can make a lot of molecules from this process. How would you decide which ones to produce?
A: We took an economic approach, and looked at all the hydrocarbon fuels which you could potentially make with CO2. Even though [molecules with more carbon atoms] are more energy dense, it takes more energy to make them. So for the current technology that we have, it makes more sense to stick with [molecules with fewer carbon atoms] such as ethylene or carbon monoxide, and then to upgrade those molecules using other processes.
Q: Is this technology ready to use now?
A: The scale-up and the advancements that have been happening in the last couple of years are really quite incredible. In terms of how close we are to industrial impact—it’s really a matter of maybe 5 to 10 years.
Q: What other methods could be used for recycling CO2 in the future?
A: In photocatalysis the driving force is sunlight [rather than electricity]. Biohybrid systems combine something like electrocatalysis or photocatalysis with enzymes or microbes that can upgrade the products of CO2 conversion into finer chemicals. Molecular machines are this idea that we could make molecular-scale factories that can take in CO2, break apart the bonds, and rearrange the atoms all on the atomic scale. That’s a really far out and optimistic idea, but … it may one day be a possibility.
Q: What do you think will decide which technology ultimately wins out?
A: At the end of the day it’s always going to be the market—which technology can get enough industrial sponsorship and acceptance from industry. That’s the one that’s going to win out, that’s the one that’ll be implemented at scale, and that’s the one the one that’ll be competitive. These large energy companies are looking for ways to diversify their portfolios and technology. And this idea … fits perfectly into what they’re skilled at, and it really hedges the bets against becoming irrelevant.