Producing syngas in a sustainable and simple way via an artificial leaf

via University of Cambridge

A widely-used gas that is currently produced from fossil fuels can instead be made by an ‘artificial leaf’ that uses only sunlight, carbon dioxide and water, and which could eventually be used to develop a sustainable liquid fuel alternative to petrol.

Being able to produce syngas sustainably would be a critical step in closing the global carbon cycle and establishing a sustainable chemical and fuel industry

The carbon-neutral device sets a new benchmark in the field of solar fuels, after researchers at the University of Cambridge demonstrated that it can directly produce the gas – called syngas – in a sustainable and simple way.

Rather than running on fossil fuels, the artificial leaf is powered by sunlight, although it still works efficiently on cloudy and overcast days. And unlike the current industrial processes for producing syngas, the leaf does not release any additional carbon dioxide into the atmosphere. The results are reported in the journal Nature Materials.

Syngas is currently made from a mixture of hydrogen and carbon monoxide, and is used to produce a range of commodities, such as fuels, pharmaceuticals, plastics and fertilisers.

“You may not have heard of syngas itself but every day, you consume products that were created using it. Being able to produce it sustainably would be a critical step in closing the global carbon cycle and establishing a sustainable chemical and fuel industry,” said senior author Professor Erwin Reisner from Cambridge’s Department of Chemistry, who has spent seven years working towards this goal.

The device Reisner and his colleagues produced is inspired by photosynthesis – the natural process by which plants use the energy from sunlight to turn carbon dioxide into food.

On the artificial leaf, two light absorbers, similar to the molecules in plants that harvest sunlight, are combined with a catalyst made from the naturally abundant element cobalt.

When the device is immersed in water, one light absorber uses the catalyst to produce oxygen. The other carries out the chemical reaction that reduces carbon dioxide and water into carbon monoxide and hydrogen, forming the syngas mixture.

As an added bonus, the researchers discovered that their light absorbers work even under the low levels of sunlight on a rainy or overcast day.

“This means you are not limited to using this technology just in warm countries, or only operating the process during the summer months,” said PhD student Virgil Andrei, first author of the paper. “You could use it from dawn until dusk, anywhere in the world.”

The research was carried out in the Christian Doppler Laboratory for Sustainable SynGas Chemistry in the University’s Department of Chemistry. It was co-funded by the Austrian government and the Austrian petrochemical company OMV, which is looking for ways to make its business more sustainable.

“OMV has been an avid supporter of the Christian Doppler Laboratory for the past seven years. The team’s fundamental research to produce syngas as the basis for liquid fuel in a carbon neutral way is ground-breaking,” said Michael-Dieter Ulbrich, Senior Advisor at OMV.

Other ‘artificial leaf’ devices have also been developed, but these usually only produce hydrogen. The Cambridge researchers say the reason they have been able to make theirs produce syngas sustainably is thanks the combination of materials and catalysts they used.

These include state-of-the-art perovskite light absorbers, which provide a high photovoltage and electrical current to power the chemical reaction by which carbon dioxide is reduced to carbon monoxide, in comparison to light absorbers made from silicon or dye-sensitised materials. The researchers also used cobalt as their molecular catalyst, instead of platinum or silver. Cobalt is not only lower-cost, but it is better at producing carbon monoxide than other catalysts.

The team is now looking at ways to use their technology to produce a sustainable liquid fuel alternative to petrol.

Syngas is already used as a building block in the production of liquid fuels. “What we’d like to do next, instead of first making syngas and then converting it into liquid fuel, is to make the liquid fuel in one step from carbon dioxide and water,” said Reisner, who is also a Fellow of St John’s College.

Although great advances are being made in generating electricity from renewable energy sources such as wind power and photovoltaics, Reisner says the development of synthetic petrol is vital, as electricity can currently only satisfy about 25% of our total global energy demand. “There is a major demand for liquid fuels to power heavy transport, shipping and aviation sustainably,” he said.

“We are aiming at sustainably creating products such as ethanol, which can readily be used as a fuel,” said Andrei. “It’s challenging to produce it in one step from sunlight using the carbon dioxide reduction reaction. But we are confident that we are going in the right direction, and that we have the right catalysts, so we believe we will be able to produce a device that can demonstrate this process in the near future.”

Learn more: ‘Artificial leaf’ successfully produces clean gas

 

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Sunlight and air produces liquid hydrocarbon fuels under real field conditions

The research plant is located on the roof of the ETH building on Sonneggstrasse. Credit: ETH Zurich / Alessandro Della Bella

Researchers from ETH Zurich have developed a novel technology that produces liquid hydrocarbon fuels exclusively from sunlight and air. For the first time worldwide they demonstrate the entire thermochemical process chain under real field conditions. The new solar mini-refinery is located on the roof of ETH’s Machine Laboratory building in Zurich.

Carbon-neutral fuels are crucial for making aviation and maritime transport sustainable. ETH researchers have developed a solar plant to produce synthetic liquid fuels that release as much CO2 during their combustion as previously extracted from the air for their production. CO2 and water are extracted directly from ambient air and split using solar energy. This process yields syngas, a mixture of hydrogen and carbon monoxide, which is subsequently processed into kerosene, methanol or other hydrocarbons. These drop-in fuels are ready for use in the existing global transport infrastructure.

Aldo Steinfeld, Professor of Renewable Energy Carriers at ETH Zurich, and his research group developed the technology. “This plant proves that carbon-neutral hydrocarbon fuels can be made from sunlight and air under real field conditions,” he explained. “The thermochemical process utilises the entire solar spectrum and proceeds at high temperatures, enabling fast reactions and high efficiency.” The research plant at the heart of Zurich advances ETH’s research towards sustainable fuels.

A small demonstration unit with big potential

The solar mini-refinery on the roof of ETH Zurich proves that the technology is feasible, even under the climate conditions prevalent in Zurich. It produces around one decilitre of fuel per day. Steinfeld and his group are already working on a large-scale test of their solar reactor in a solar tower near Madrid, which is carried out within the scope of the EU project sun-to-liquid. The solar tower plant is presented to the public in Madrid at the same time today as the mini-refinery in Zurich.

The next project goal is to scale the technology for industrial implementation and make it economically competitive. “A solar plant spanning an area of one square kilometre could produce 20,000 litres of kerosene a day,” said Philipp Furler, Director (CTO) of Synhelion and a former doctoral student in Steinfeld’s group. “Theoretically, a plant the size of Switzerland – or a third of the Californian Mojave Desert – could cover the kerosene needs of the entire aviation industry. Our goal for the future is to efficiently produce sustainable fuels with our technology and thereby mitigate global CO2 emissions.”

Two spin-offs already

Two spin-offs already emerged from Aldo Steinfeld’s research group: Synhelion, founded in 2016, commercializes the solar fuel production technology. Climeworks, founded already in 2010, commercialises the technology for CO2 capture from air.

How the new solar mini-refinery works

The process chain of the new system combines three thermochemical conversion processes: Firstly, the extraction of CO2 and water from the air. Secondly, the solar-thermochemical splitting of CO2 and water. Thirdly, their subsequent liquefaction into hydrocarbons. CO2 and water are extracted directly from ambient air via an adsorption/desorption process. Both are then fed into the solar reactor at the focus of a parabolic reflector. Solar radiation is concentrated by a factor of 3,000, generating process heat at a temperature of 1,500 degrees Celsius inside the solar reactor. At the heart of the solar reactor is a ceramic structure made of cerium oxide, which enables a two-step reaction – the redox cycle – to split water and CO2 into syngas. This mixture of hydrogen and carbon monoxide can then be processed into liquid hydrocarbon fuels through conventional methanol or Fischer–Tropsch synthesis.

Learn more: Carbon-neutral fuel made from sunlight and air

 

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More carbon neutral fuels progress

via EPFL

Chemists at EPFL have developed an efficient process for converting carbon dioxide into carbon monoxide, a key ingredient of synthetic fuels and materials.

The carbon dioxide (CO2) produced when fossil fuels are burned is normally released into the atmosphere. Researchers working on synthetic fuels – also known as carbon-neutral fuels – are exploring ways to capture and recycle that CO2. At EPFL, this research is spearheaded by a team led by Professor Xile Hu at the Laboratory of Inorganic Synthesis and Catalysis (LSCI). The chemists have recently made a landmark discovery, successfully developing a high-efficiency catalyst that converts dissolved CO2 into carbon monoxide (CO) – an essential ingredient of all synthetic fuels, as well as plastics and other materials. The researchers published their findings in Science on 14 June.

Replacing gold with iron

The new process is just as efficient as previous technologies, but with one major benefit. “To date, most catalysts have used atoms of precious metals such as gold,” explains Professor Hu. “But we’ve used iron atoms instead. At extremely low currents, our process achieves conversion rates of around 90%, meaning it performs on a par with precious-metal catalysts.”

“Our catalyst converts such a high percentage of CO2 into CO because we successfully stabilized iron atoms to achieve efficient CO2 activation,” adds Jun Gu, a PhD student and lead author of the paper. To help them understand why their catalyst was so highly active, the researchers called on a team led by Professor Hao Ming Chen at National Taiwan University, who conducted a key measurement of the catalyst under operating conditions using synchrotron X-rays.

Closing the carbon cycle

Although the team’s work is still very much experimental, the research paves the way for new applications. At present, most of the carbon monoxide needed to make synthetic materials is obtained from petroleum. Recycling the carbon dioxide produced by burning fossil fuels would help preserve precious resources, as well as limit the amount of CO2 – a major greenhouse gas – released into the atmosphere.

The process could also be combined with storage batteries and hydrogen-production technologies to convert surplus renewable power into products that could fill the gap when demand outstrips supply.

Learn more: Carbon-neutral fuels move a step closer

 

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