New solar-powered system converts harmful emissions into sustainable fuels

Researchers from the University of Cambridge have developed a system that can transform plastic waste and greenhouse gases into sustainable fuels and other valuable products – using only energy from the Sun.

The system is a one-of-a-kind invention, being the only solar-powered reactor that can convert two waste streams into two chemical products at the same time.

The reactor converts carbon dioxide (CO2) and plastics into sustainable fuels that are useful in a range of different industries. During the testing stage, CO2 was converted into syngas, an important building block for sustainable liquid fuels. Moreover, plastic bottles were converted into glycolic acid, which is widely used in the cosmetics industry. The system can be easily tuned to produce different products by changing the type of catalyst used in the reactor.

Converting these harmful substances, which are two of the biggest threats facing the natural world, into sustainable fuels using solar energy is an important step in the transition to a more sustainable, circular economy. The results of the study were reported in the journal Nature Synthesis.

Combining recycling technologies into a single process

“Converting waste into sustainable fuels using solar energy is a major goal of our research,” said Professor Erwin Reisner from the Yusuf Hamied Department of Chemistry and the paper’s senior author. “Plastic pollution is a huge problem worldwide, and often, many of the plastics we throw into recycling bins are incinerated or end up in landfill.”

Reisner also leads the Cambridge Circular Plastics Centre (CirPlas), which aims to eliminate plastic waste by combining blue-sky thinking with practical measures.

Alternative solar-powered recycling technologies have also held promise for addressing plastic pollution and for reducing the amount of greenhouse gases in the atmosphere. However, so far, they have not been combined into a single process.

“A solar-driven technology that could help to address plastic pollution and greenhouse gases at the same time could be a game-changer in the development of a circular economy,” commented Subhajit Bhattacharjee, the paper’s co-first author.

Another co-first author, Dr Motiar Rahaman, added: “We also need something that’s tuneable, so that you can easily make changes depending on the final product you want.”

To address these concerns, the team developed an integrated reactor with two separate compartments to create separate sustainable fuels for the different products. The reactor uses a light absorber based on perovskite – a promising alternative to silicon for next-generation solar cells.

What makes this system different to previous designs?

The team designed different catalysts, which were integrated into the light absorber. By changing the catalyst, the end product was still able to be changed.

Tests on the reactor under normal temperature and pressure conditions showed that it could efficiently convert PET plastic bottles and CO2 into different sustainable fuels, such as CO, syngas, or formate, as well as glycolic acid.

The Cambridge-developed reactor produced these sustainable fuels at a rate that is much higher than conventional photocatalytic CO2 reduction processes.

“Generally, CO2 conversion requires a lot of energy, but with our system, basically you just shine a light at it, and it starts converting harmful products into something useful and sustainable,” explained Rahaman. “Prior to this system, we didn’t have anything that could make high-value products selectively and efficiently.”

“What’s so special about this system is the versatility and tuneability – we’re making fairly simple carbon-based molecules right now, but in future, we could be able to tune the system to make far more complex products, just by changing the catalyst,” Bhattacharjee added.

Addressing the climate crisis through reactor-produced sustainable fuels

Reisner and his team recently received new funding from the European Research Council to help the development of sustainable fuels through their solar-powered reactor. Over the next five years, they are aiming to further develop the reactor to produce more complex molecules.

According to the researchers, similar techniques to this one could be used someday to develop an entirely solar-powered recycling plant.

“Developing a circular economy where we make useful, sustainable fuels from waste instead of throwing it into landfill is vital if we’re going to meaningfully address the climate crisis and protect the natural world,” Reisner concluded. “And powering these solutions using the Sun means that we’re doing it cleanly and sustainably.”

The research was supported in part by the European Union, the European Research Council, the Cambridge Trust, Hermann and Marianne Straniak Stiftung, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

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