Clean, Sustainable Fuels Made from ‘Thin Air’ and Plastic Waste

Andrew Corselli

Researchers have demonstrated how carbon dioxide can be captured from industrial processes — or even directly from the air — and transformed into clean, sustainable fuels using just the energy from the sun.

The University of Cambridge researchers developed a solar-powered reactor that converts captured CO₂ and plastic waste into sustainable fuels and other valuable chemical products. In tests, CO₂ was converted into syngas, a key building block for sustainable liquid fuels, and plastic bottles were converted into glycolic acid, which is widely used in the cosmetics industry.

“We’re not just interested in decarbonization, but de-fossilization – we need to completely eliminate fossil fuels in order to create a truly circular economy,” said Professor Erwin Reisner. “In the medium term, this technology could help reduce carbon emissions by capturing them from industry and turning them into something useful, but ultimately, we need to cut fossil fuels out of the equation entirely and capture CO₂ from the air.”

The researchers adapted their solar-driven technology so that it works with flue gas or directly from the air, converting CO₂ and plastics into fuel and chemicals using only the power of the sun.

Here is an exclusive Tech Briefs interview, edited for clarity and length, with co-first authors Dr. Motiar Rahaman and Dr. Sayan Kar.

Tech Briefs: Can you explain in simple terms how the technology works please?

Kar: Basically, at the heart of it is a two-compartment reactor. And in one compartment we have carbon dioxide capture and conversion, so we pass air or exhaust gas through it. What it does is it selectively captures the carbon dioxide in solution, and it traps it there. And on the other side, we take plastic and we put it in the other compartment, and then we shine sunlight on it. Then what happens is that the captured carbon dioxide is converted into fuel, and the plastic gets converted into a pharmaceutical product — glycolic acid.

Tech Briefs: While designing this technology, what were the biggest technical challenges you faced?

Rahaman: Carbon dioxide conversion is itself a challenging process, and sunlight-driven carbon dioxide conversion is a challenging process. We’re trying to combine the carbon capture and conversion processes together in an integrated process. When you want to convert carbon dioxide, people generally use water oxidation as a counter reaction, and it actually doesn’t work with a counter water oxidation reaction. So, we couple plastic reforming on one side with the captured carbon dioxide conversion on the other.

The main challenge is to make the system autonomous and solely sunlight-driven. Here, our system is completely light-driven without any applied energy or without any external bias. We have a photo electrode on one side; on the other side, a photo electrode does the carbon dioxide conversion — it absorbs sunlight, it converts sunlight into photo voltage, and it does the captured carbon dioxide conversion into syngas, which is carbon monoxide and hydrogen, that can be converted further into liquid hydrocarbon. And a dark anode converts plastic into glycolic acid. So, we connect these two electrodes in two compartments for photo electrochemical reactions, and with sunlight it’s self-driven without any external bias.

Tech Briefs: How long do you estimate it’ll be before we see the technology implemented at an industrial scale?

Kar: We’ve shown the proof of concept — we can do it driven solely by sunlight. But, efficiency-wise, it’s still not as far as we expect for the industrial process. We are trying to improve the efficiencies and the durability of the system. But I would say at least a decade or so — not anytime soon.

Tech Briefs: The team is currently working on a benchtop demonstrator device with improved efficiency and practicality to highlight the benefits of coupling direct air capture with CO₂utilization. How is that coming along? Do you have any updates or any info you could provide on that?

Rahaman: We have a lab-scale reactor, which is what we use as a photo electrochemical cell to demonstrate that the experiment is possible. So now to bring it to the industrial scale, it will take some time and we need to optimize all the other components. We have to make the photo electrodes bigger, we have to make a big reactor, and then we might use the natural sunlight to convert this captured carbon dioxide along with the plastic reforming.

One important part is we need to improve the efficiency of carbon capture, the efficiency of the photo absorber. We need to improve the the solar cell, so it absorbs sunlight more efficiently and then transforms it into photo voltage. So, more step-by-step optimizations are required and then it needs to be implemented at a large scale.

So, basically, the scientific thing is there, but the next part is more or less the technical part to make it at a large scale.

Tech Briefs: What’s the next step? What’s your next move?

Kar: We want to improve the rates. Right now, when we use post-combustion flue gas we get decent rates, but when we move to air as the carbon dioxide source — because carbon dioxide in air is so dilute — it’s almost 0.04 percent. So, we want to focus a little bit on improving the performance in the lab scale. And then after that we will think about how to scale it up. But, right now, we are basically fine-tuning the system to get as much fuel as quickly as possible.

Tech Briefs: Is there anything else you’d like to add?

Rahaman: People have already achieved the process of carbon capture and conversion, using electricity — electrical energy. This is the first report, however, which shows that by using direct sunlight or solar energy it is possible to convert captured carbon dioxide into syngas in addition to simultaneously converting plastic waste into a chemical. So, it’s like two processes combined.

Kar: Carbon capture from air is getting huge momentum nowadays — basically the idea has been that we can take CO₂ from air and then store it underground . But the long-term consequences of such storage are still unknown. So, what our study shows is that we can instead use sunlight to convert carbon dioxide into fuel. Thus, the cycle is carbon-neutral throughout.

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