Scientists invent solar device to convert waste into clean energy

“We urgently require new innovations for a sustainable future and this work is a real advance in creating a circular economy”

Plastic rubbish such as single-use drinks bottles could be turned into chemicals to make skincare products after scientists built a sunlight-powered reactor to recycle environmental waste.  

In a world-first, scientists can now also convert harmful greenhouse gases into renewable energy using the hand-held solar-powered prototype.

The results of the ground-breaking work by researchers from St John’s College, University of Cambridge, was published on 9th January in the journal, Nature Synthesis. It is hoped the device, which is the size of a coffee mug, will be scaled-up to help the world move away from relying on fossil fuels to using sustainable green energy. 

Professor Erwin Reisner, Professor of Energy and Sustainability from the Yusuf Hamied Department of Chemistry, a Fellow of St John’s College and senior author of the paper, said: “This is the first solar-powered reactor that can simultaneously convert carbon dioxide to fuel and upcycle plastic waste into something useful. 

“It’s all done by sunlight at ambient room temperature, so there’s no need for another external energy source, which will make it easier to scale up and use in economies anywhere in the world.”

(From left) Professor Erwin Reisner, Subhajit Bhattacharjee and Dr Motiar Rahaman with the solar reactor that can simultaneously convert carbon dioxide into clean fuels and upcycle plastics into glycolic acid, a useful organic chemical for skincare creams.
(From left) Professor Erwin Reisner, Subhajit Bhattacharjee and Dr Motiar Rahaman with the solar reactor that can simultaneously convert carbon dioxide into clean fuels and upcycle plastics into glycolic acid, a useful organic chemical for skincare creams.

Powered by sunlight, the photoelectrochemical reactor converts carbon dioxide gas and plastics in two separate compartments, eradicating two different waste streams in one fell swoop. Three types of renewable fuels can be generated by the carbon dioxide conversion while the plastics are transformed into glycolic acid – an organic chemical used in skincare products, such as acne cream, in the pharmaceutical and cosmetic industries.

Carbon dioxide is released into our atmosphere from the burning of fossil fuels, such as coal, oil and natural gas, to create energy, as well as from other sources in nature including volcanoes and plant decay. In the Earth’s atmosphere carbon dioxide acts as a greenhouse gas, which is a main cause of accelerating global warming and climate change.

The new reactor uses a photoelectrode for carbon dioxide conversion and another electrode to turn the polyethylene terephthalate (PET) plastics into glycolic acid. The photocathode consists of a solar harvesting material that extracts energy from sunlight to generate power and a catalyst to facilitate the process.

The researchers found that by using various catalysts, carbon dioxide can be transformed into different kinds of clean and renewable fuels such as carbon monoxide, syngas (also known as synthesis gas) and formic acid – a liquid energy carrier. 

“We hope to achieve targeted production of high energy density fuels and commodity chemicals on demand for different purposes”

Professor Reisner said: “Our group has been working for several years on simpler systems that can make hydrogen from plastics. But this coupling of processes in a single reactor allows us to convert carbon dioxide into fuel for the first time. Carbon dioxide is an attractive raw material for this because it’s a greenhouse gas and, ultimately, if you'd like to make liquid fuels or some high dense fuels, you really want to make it from carbon dioxide to close the global carbon cycle.

“We urgently require new innovations for a sustainable future and this work is a real advance in creating a circular economy, a proof of concept that also translates into record performance in the field of sunlight-driven devices.”

Subhajit Bhattacharjee, the co-first author of the paper, who is a PhD student at St John’s, said: “Along with efforts to mitigate carbon emissions from different sectors, the development of sustainable technologies to convert carbon dioxide to renewable fuels is important and attractive. At the same time, new strategies to upcycle non-biodegradable plastics must come up.

“We have found a way of tackling these challenges simultaneously and combining all this chemistry in a simple, integrated and efficient process driven by sunlight.”

Solar reactor.
The solar reactor.

“The key strength of this integrated solar-powered system is its tunability. It allows us to generate a large number of high value products from waste by modifying the electrode configuration. With improved design over the next few years, we hope to achieve targeted production of high energy density fuels and commodity chemicals on demand for different purposes,” said Dr Motiar Rahaman, co-first author of the paper and a College Research Associate at St John’s.

The group’s next step is to make the solar device even more efficient and experiment with different catalyst systems and waste streams to find out what other chemicals and fuel substitutes could be produced, such as alcohols, kerosene or gasoline. They hope the processes will have an impact on the energy and chemicals industry, making them greener in the future. 

Nature Synthesis article

Published 13/01/2023

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