Driving on sunshine: clean liquid fuels generated from solar power and CO2
[May 19, 2023: Staff Writer, The Brighter Side of News]
Most solar cells are currently silicon based; however, their efficiency is limited. (CREDIT: Creative Commons)
Scientists have created a solar-powered mechanism that transforms carbon dioxide and water into liquid fuels. These fuels can be used as an immediate alternative in car engines.
The team, based at the University of Cambridge, utilized the process of photosynthesis to transmute CO2, water, and sunlight into multicarbon fuels like ethanol and propanol in one go. These fuels are characterized by high energy density and the ease with which they can be stored or transported.
Contrary to fossil fuels, these solar-generated fuels result in net zero carbon emissions and are completely renewable. Additionally, they do not lead to the misappropriation of agricultural land for non-food purposes, unlike many bioethanol sources.
Despite being in the experimental phase and primarily demonstrated at lab scale, the team asserts that their 'artificial leaves' present a significant development in moving away from a fossil fuel-dependent economy. The findings are documented in the scientific journal Nature Energy.
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Bioethanol is often proposed as a more environmentally friendly alternative to petrol, being plant-derived rather than fossil fuel-based. Most of today's cars and trucks operate on petrol with up to 10% ethanol content, known as E10 fuel. The US is the largest bioethanol producer globally; the U.S. Department of Agriculture reports that nearly 45% of all corn grown in the US is used for ethanol production.
Lead researcher Professor Erwin Reisner said, “Biofuels like ethanol are a controversial technology, not least because they take up agricultural land that could be used to grow food instead.”
For many years, the research team led by Reisner at the Yusuf Hamied Department of Chemistry has been tirelessly working on the creation of eco-friendly, zero-carbon fuels. These are inspired by the photosynthetic process, in which plants transform solar energy into nutrients, and are being crafted through the medium of synthetic leaves.
A photoreactor with an artificial leaf working under solar irradiation. (CREDIT: Motiar Rahaman)
In the past, these synthetic leaves were only capable of generating simple compounds like syngas - a combination of hydrogen and carbon monoxide employed in the production of fuels, pharmaceuticals, plastics, and fertilisers. However, to enhance the practicality of the technology, it needs to be upgraded to manufacture more intricate chemicals in a single step powered by solar energy.
In a significant advancement, the synthetic leaf can now directly generate clean ethanol and propanol, thereby eliminating the intermediate phase of syngas production.
A standalone artificial leaf attached to a metal rod support. The photoanode side (green square) is visible in the photograph. (CREDIT: Motiar Rahaman)
To enable the process, the research team devised a catalyst based on copper and palladium. This catalyst was fine-tuned to enable the synthetic leaf to manufacture more intricate chemicals, specifically the multicarbon alcohols ethanol and n-propanol. Both these alcohols are high energy density fuels which are easy to transport and store.
While other scientists have succeeded in manufacturing similar chemicals using electrical power, this marks the first occasion such intricate chemicals have been created with a synthetic leaf, powered solely by solar energy.
“Shining sunlight on the artificial leaves and getting liquid fuel from carbon dioxide and water is an amazing bit of chemistry,” said Dr Motiar Rahaman, the paper’s first author.
“Normally, when you try to convert CO2 into another chemical product using an artificial leaf device, you almost always get carbon monoxide or syngas, but here, we’ve been able to produce a practical liquid fuel just using the power of the Sun. It’s an exciting advance that opens up whole new avenues in our work,” he continued.
Currently, the device merely exists as a prototype, demonstrating only a fair degree of efficiency. The researchers are in the process of enhancing the light absorbers for superior sunlight absorption and refining the catalyst to increase its capacity to convert sunlight into fuel. Additionally, considerable efforts are needed to scale up the device for it to generate substantial amounts of fuel.
“Even though there’s still work to be done, we’ve shown what these artificial leaves are capable of doing,” said Reisner. “It’s important to show that we can go beyond the simplest molecules and make things that are directly useful as we transition away from fossil fuels.”
The research received funding support from various sources, including the European Commission Marie Skłodowska-Curie Fellowship, the Cambridge Trust, and the Winton Programme for the Physics of Sustainability. Both Erwin Reisner and Motiar Rahaman are affiliated with St John's College, Cambridge, with Reisner as a Fellow and Rahaman as a Research Associate.
For more science news stories check out our New Innovations section at The Brighter Side of News.
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