Inexpensive, carbon-neutral biofuels are finally possible

When it comes to making fuel from plants, the first step has always been the hardest -- breaking down the plant matter. A new study finds that introducing a simple, renewable chemical to the pretreatment step can finally make next-generation biofuel production both cost-effective and carbon neutral.

For biofuels to compete with petroleum, biorefinery operations must be designed to better utilize lignin. Lignin is one of the main components of plant cell walls. It provides plants with greater structural integrity and resiliency from microbial attacks. However, these natural properties of lignin also make it difficult to extract and utilize from the plant matter, also known as biomass.

"Lignin utilization is the gateway to making what you want out of biomass in the most economical and environmentally friendly way possible," said UC Riverside Associate Research Professor Charles Cai. "Designing a process that can better utilize both the lignin and sugars found in biomass is one of the most exciting technical challenges in this field."

To overcome the lignin hurdle, Cai invented CELF, which stands for co-solvent enhanced lignocellulosic fractionation. It is an innovative biomass pretreatment technology.

"CELF uses tetrahydrofuran or THF to supplement water and dilute acid during biomass pretreatment. It improves overall efficiency and adds lignin extraction capabilities," Cai said. "Best of all, THF itself can be made from biomass sugars."

A landmark Energy & Environmental Science paper details the degree to which a CELF biorefinery offers economic and environmental benefits over both petroleum-based fuels and earlier biofuel production methods.

The paper is a collaboration between Cai's research team at UCR, the Center for Bioenergy Innovation managed by Oak Ridge National Laboratories, and the National Renewable Energy Laboratory, with funding provided by the U.S. Department of Energy's Office of Science. In it, the researchers consider two main variables: what kind of biomass is most ideal and what to do with the lignin once it's been extracted.

First-generation biofuel operations use food crops like corn, soy, and sugarcane as raw materials, or feedstocks. Because these feedstocks divert land and water away from food production, using themfor biofuels is not ideal.

Second-generation operations use non-edible plant biomass as feedstocks. An example of biomass feedstocks includes wood residues from milling operations, sugarcane bagasse, or corn stover, all of which are abundant low-cost byproducts of forestry and agricultural operations.

According to the Department of Energy, up to a billion tons per year of biomass could be made available for the manufacture of biofuels and bioproducts in the US alone, capable of displacing 30% of our petroleum consumption while also creating new domestic jobs.

Because a CELF biorefinery can more fully utilize plant matter than earlier second-generation methods, the researchers found that a heavier, denser feedstock like hardwood poplar is preferable over less carbon-dense corn stover for yielding greater economic and environmental benefits.

Using poplar in a CELF biorefinery, the researchers demonstrate that sustainable aviation fuel could be made at a break-even price as low as $3.15 per gallon of gasoline equivalent. The current average cost for a gallon of jet fuel in the U.S. is $5.96.

The U.S. government issues credits for biofuel production in the form of renewable identification number credits, a subsidy meant to bolster domestic biofuel production. The tier of these credits issued for second-generation biofuels, the D3 tier, is typically traded at $1 per gallon or higher. At this price per credit, the paper demonstrates that one can expect a rate of return of over 20% from the operation.

"Spending a little more for a more carbon-rich feedstock like poplar still yields more economic benefits than a cheaper feedstock like corn stover, because you can make more fuel and chemicals from it," Cai said.

The paper also illustrates how lignin utilization can positively contribute to overall biorefinery economics while keeping the carbon footprint as low as possible. In older biorefinery models, where biomass is cooked in water and acid, the lignin is mostly unusable for more than its heating value.

"The older models would elect to burn the lignin to supplement heat and energy for these biorefineries because they could mostly only leverage the sugars in the biomass -- a costly proposition that leaves a lot of value off the table," said Cai.

In addition to better lignin utilization, the CELF biorefinery model also proposes to produce renewable chemicals. These chemicals could be used as building blocks for bioplastics and food and drink flavoring compounds. These chemicals take up some of the carbon in the plant biomass that would not get released back into the atmosphere as CO2.

"Adding THF helps reduce the energy cost of pretreatment and helps isolate lignin, so you wouldn't have to burn it anymore. On top of that, we can make renewable chemicals that help us achieve a near-zero global warming potential," Cai said. "I think this moves the needle from Gen 2 biofuels to Gen 2+."

In light of the team's recent successes, the Department of Energy's Bioenergy Technology Office has awarded the researchers a $2 million grant to build a small-scale CELF pilot plant at UCR. Cai hopes that demonstrating the pilot plant will lead to larger-scale investment in the technology, as harnessing energy from fossil fuels adds to global warming and hurts the planet.

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Engineers develop an efficient process to make fuel from carbon dioxide

The search is on worldwide to find ways to extract carbon dioxide from the air or from power plant exhaust and then make it into something useful. One of the more promising ideas is to make it into a stable fuel that can replace fossil fuels in some applications. But most such conversion processes have had problems with low carbon efficiency, or they produce fuels that can be hard to handle, toxic, or flammable.

Now, researchers at MIT and Harvard University have developed an efficient process that can convert carbon dioxide into formate, a liquid or solid material that can be used like hydrogen or methanol to power a fuel cell and generate electricity. Potassium or sodium formate, already produced at industrial scales and commonly used as a de-icer for roads and sidewalks, is nontoxic, nonflammable, easy to store and transport, and can remain stable in ordinary steel tanks to be used months, or even years, after its production.

The new process, developed by MIT doctoral students Zhen Zhang, Zhichu Ren, and Alexander H. Quinn, Harvard University doctoral student Dawei Xi, and MIT Professor Ju Li, is described this week in the journal Cell Press Physical Sciences. The whole process -- including capture and electrochemical conversion of the gas to a solid formate powder, which is then used in a fuel cell to produce electricity -- was demonstrated at a small, laboratory scale. However, the researchers expect it to be scalable so that it could provide emissions-free heat and power to individual homes and even be used in industrial or grid-scale applications.

Other approaches to converting carbon dioxide into fuel, Li explains, usually involve a two-stage process: First the gas is chemically captured and turned into a solid form as calcium carbonate, then later that material is heated to drive off the carbon dioxide and convert it to a fuel feedstock such as carbon monoxide. That second step has very low efficiency, typically converting less than 20 percent of the gaseous carbon dioxide into the desired product, Li says.

By contrast, the new process achieves a conversion of well over 90 percent and eliminates the need for the inefficient heating step by first converting the carbon dioxide into an intermediate form, liquid metal bicarbonate. That liquid is then electrochemically converted into liquid potassium or sodium formate in an electrolyzer that uses low-carbon electricity, e.g. nuclear, wind, or solar power. The highly concentrated liquid potassium or sodium formate solution produced can then be dried, for example by solar evaporation, to produce a solid powder that is highly stable and can be stored in ordinary steel tanks for up to years or even decades, Li says.

Several steps of optimization developed by the team made all the difference in changing an inefficient chemical-conversion process into a practical solution, says Li, who holds joint appointments in the departments of Nuclear Science and Engineering and of Materials Science and Engineering.

The process of carbon capture and conversion involves first an alkaline solution based capture that concentrates carbon dioxide, either from concentrated streams such as from power plant emissions or from very low-concentration sources, even open air, into the form of a liquid metal-bicarbonate solution. Then, through the use of a cation-exchange membrane electrolyzer, this bicarbonate is electrochemically converted into solid formate crystals with a carbon efficiency of greater than 96 percent, as confirmed in the team's lab-scale experiments.

These crystals have an indefinite shelf life, remaining so stable that they could be stored for years, or even decades, with little or no loss. By comparison, even the best available practical hydrogen storage tanks allow the gas to leak out at a rate of about 1 percent per day, precluding any uses that would require year-long storage, Li says. Methanol, another widely explored alternative for converting carbon dioxide into a fuel usable in fuel cells, is a toxic substance that cannot easily be adapted to use in situations where leakage could pose a health hazard. Formate, on the other hand, is widely used and considered benign, according to national safety standards.

Several improvements account for the greatly improved efficiency of this process. First, a careful design of the membrane materials and their configuration overcomes a problem that previous attempts at such a system have encountered, where a buildup of certain chemical byproducts changes the pH, causing the system to steadily lose efficiency over time. "Traditionally, it is difficult to achieve long-term, stable, continuous conversion of the feedstocks," Zhang says. "The key to our system is to achieve a pH balance for steady-state conversion."

To achieve that, the researchers carried out thermodynamic modeling to design the new process so that it is chemically balanced and the pH remains at a steady state with no shift in acidity over time. It can therefore can continue operating efficiently over long periods. In their tests, the system ran for over 200 hours with no significant decrease in output. The whole process can be done at ambient temperatures and relatively low pressures (about five times atmospheric pressure).

Another issue was that unwanted side reactions produced other chemical products that were not useful, but the team figured out a way to prevent these side reactions by the introduction of an extra "buffer" layer of bicarbonate-enriched fiberglass wool that blocked these reactions.

The team also built a fuel cell specifically optimized for the use of this formate fuel to produce electricity. The stored formate particles are simply dissolved in water and pumped into the fuel cell as needed. Although the solid fuel is much heavier than pure hydrogen, when the weight and volume of the high-pressure gas tanks needed to store hydrogen is considered, the end result is an electricity output near parity for a given storage volume, Li says.

The formate fuel can potentially be adapted for anything from home-sized units to large scale industrial uses or grid-scale storage systems, the researchers say. Initial household applications might involve an electrolyzer unit about the size of a refrigerator to capture and convert the carbon dioxide into formate, which could be stored in an underground or rooftop tank. Then, when needed, the powdered solid would be mixed with water and fed into a fuel cell to provide power and heat. "This is for community or household demonstrations," Zhang says, "but we believe that also in the future it may be good for factories or the grid."

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Clean, sustainable fuels made 'from thin air' and plastic waste

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 researchers, from the University of Cambridge, 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.

Unlike earlier tests of their solar fuels technology however, the team took CO2 from real-world sources -- such as industrial exhaust or the air itself. The researchers were able to capture and concentrate the CO2 and convert it into sustainable fuel.

Although improvements are needed before this technology can be used at an industrial scale, the results, reported in the journal Joule, represent another important step toward the production of clean fuels to power the economy, without the need for environmentally destructive oil and gas extraction.

For several years, Professor Erwin Reisner's research group, based in the Yusuf Hamied Department of Chemistry, has been developing sustainable, net-zero carbon fuels inspired by photosynthesis -- the process by which plants convert sunlight into food -- using artificial leaves. These artificial leaves convert CO2 and water into fuels using just the power of the sun.

To date, their solar-driven experiments have used pure, concentrated CO2 from a cylinder, but for the technology to be of practical use, it needs to be able to actively capture CO2 from industrial processes, or directly from the air. However, since CO2 is just one of many types of molecules in the air we breathe, making this technology selective enough to convert highly diluted CO2 is a huge technical challenge.

"We're not just interested in decarbonisation, but de-fossilisation -- we need to completely eliminate fossil fuels in order to create a truly circular economy," said 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 took their inspiration from carbon capture and storage (CCS), where CO2 is captured and then pumped and stored underground.

"CCS is a technology that's popular with the fossil fuel industry as a way to reduce carbon emissions while continuing oil and gas exploration," said Reisner. "But if instead of carbon capture and storage, we had carbon capture and utilisation, we could make something useful from CO2 instead of burying it underground, with unknown long-term consequences, and eliminate the use of fossil fuels."

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.

By bubbling air through the system containing an alkaline solution, the CO2 selectively gets trapped, and the other gases present in air, such as nitrogen and oxygen, harmlessly bubble out. This bubbling process allows the researchers to concentrate the CO2 from air in solution, making it easier to work with.

The integrated system contains a photocathode and an anode. The system has two compartments: on one side is captured CO2 solution that gets converted into syngas, a simple fuel. On the other plastics are converted into useful chemicals using only sunlight.

"The plastic component is an important trick to this system," said co-first author Dr Motiar Rahaman. "Capturing and using CO2 from the air makes the chemistry more difficult. But, if we add plastic waste to the system, the plastic donates electrons to the CO2. The plastic breaks down to glycolic acid, which is widely used in the cosmetics industry, and the CO2 is converted into syngas, which is a simple fuel."

"This solar-powered system takes two harmful waste products -- plastic and carbon emissions -- and converts them into something truly useful," said co-first author Dr Sayan Kar.

"Instead of storing CO2 underground, like in CCS, we can capture it from the air and make clean fuel from it," said Rahaman. "This way, we can cut out the fossil fuel industry from the process of fuel production, which can hopefully help us avoid climate destruction."

"The fact that we can effectively take CO2 from air and make something useful from it is special," said Kar. "It's satisfying to see that we can actually do it using only sunlight."

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Astronomers spot a star swallowing a planet

As a star runs out of fuel, it will billow out to a million times its original size, engulfing any matter -- and planets -- in its wake. Scientists have observed hints of stars just before, and shortly after, the act of consuming entire planets, but they have never caught one in the act until now.

In a study that will appear in Nature, scientists at MIT, Harvard University, Caltech, and elsewhere report that they have observed a star swallowing a planet, for the first time.

The planetary demise appears to have taken place in our own galaxy, some 12,000 light-years away, near the eagle-like constellation Aquila. There, astronomers spotted an outburst from a star that became more than 100 times brighter over just 10 days, before quickly fading away. Curiously, this white-hot flash was followed by a colder, longer-lasting signal. This combination, the scientists deduced, could only have been produced by one event: a star engulfing a nearby planet.

"We were seeing the end-stage of the swallowing," says lead author Kishalay De, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research.

What of the planet that perished? The scientists estimate that it was likely a hot, Jupiter-sized world that spiraled close, then was pulled into the dying star's atmosphere, and, finally, into its core.

A similar fate will befall the Earth, though not for another 5 billion years, when the sun is expected to burn out, and burn up the solar system's inner planets.

"We are seeing the future of the Earth," De says. "If some other civilization was observing us from 10,000 light-years away while the sun was engulfing the Earth, they would see the sun suddenly brighten as it ejects some material, then form dust around it, before settling back to what it was."

The study's MIT co-authors include Deepto Chakrabarty, Anna-Christina Eilers, Erin Kara, Robert Simcoe, Richard Teague, and Andrew Vanderburg, along with colleagues from Caltech, the Harvard and Smithsonian Center for Astrophysics, and multiple other institutions.

Hot and cold

The team discovered the outburst in May 2020. But it took another year for the astronomers to piece together an explanation for what the outburst could be.

The initial signal showed up in a search of data taken by the Zwicky Transient Facility (ZTF), run at Caltech's Palomar Observatory in California. The ZTF is a survey that scans the sky for stars that rapidly change in brightness, the pattern of which could be signatures of supernovae, gamma-ray bursts, and other stellar phenomena.

De was looking through ZTF data for signs of eruptions in stellar binaries -- systems in which two stars orbit each other, with one pulling mass from the other every so often and brightening briefly as a result.

"One night, I noticed a star that brightened by a factor of 100 over the course of a week, out of nowhere," De recalls. "It was unlike any stellar outburst I had seen in my life."

Hoping to nail down the source with more data, De looked to observations of the same star taken by the Keck Observatory in Hawaii. The Keck telescopes take spectroscopic measurements of starlight, which scientists can use to discern a star's chemical composition.

But what De found further befuddled him. While most binaries give off stellar material such as hydrogen and helium as one star erodes the other, the new source gave off neither. Instead, what De saw were signs of "peculiar molecules" that can only exist at very cold temperatures.

"These molecules are only seen in stars that are very cold," De says. "And when a star brightens, it usually becomes hotter. So, low temperatures and brightening stars do not go together."

"A happy coincidence"

It was then clear that the signal was not of a stellar binary. De decided to wait for more answers to emerge. About a year after his initial discovery, he and his colleagues analyzed observations of the same star, this time taken with an infrared camera at the Palomar Observatory. Within the infrared band, astronomers can see signals of colder material, in contrast to the white-hot, optical emissions that arise from binaries and other extreme stellar events.

"That infrared data made me fall off my chair," De says. "The source was insanely bright in the near-infrared."

It seemed that, after its initial hot flash, the star continued to throw out colder energy over the next year. That frigid material was likely gas from the star that shot into space and condensed into dust, cold enough to be detected at infrared wavelengths. This data suggested that the star could be merging with another star rather than brightening as a result of a supernovae explosion.

But when the team further analyzed the data and paired it with measurements taken by NASA's infrared space telescope, NEOWISE, they came to a much more exciting realization. From the compiled data, they estimated the total amount of energy released by the star since its initial outburst, and found it to be surprisingly small -- about 1/1,000 the magnitude of any stellar merger observed in the past.

"That means that whatever merged with the star has to be 1,000 times smaller than any other star we've seen," De says. "And it's a happy coincidence that the mass of Jupiter is about 1/1,000 the mass of the sun. That's when we realized: This was a planet, crashing into its star."

With the pieces in place, the scientists were finally able to explain the initial outburst. The bright, hot flash was likely the final moments of a Jupiter-sized planet being pulled into a dying star's ballooning atmosphere. As the planet fell into the star's core, the outer layers of the star blasted away, settling out as cold dust over the next year.

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How a record-breaking copper catalyst converts CO2 into liquid fuels

Since the 1970s, scientists have known that copper has a special ability to transform carbon dioxide into valuable chemicals and fuels. But for many years, scientists have struggled to understand how this common metal works as an electrocatalyst, a mechanism that uses energy from electrons to chemically transform molecules into different products.

Now, a research team led by Lawrence Berkeley National Laboratory (Berkeley Lab) has gained new insight by capturing real-time movies of copper nanoparticles (copper particles engineered at the scale of a billionth of a meter) as they convert CO2 and water into renewable fuels and chemicals: ethylene, ethanol, and propanol, among others. The work was reported in the journal Nature last week.

"This is very exciting. After decades of work, we're finally able to show -- with undeniable proof -- how copper electrocatalysts excel in CO2 reduction," said Peidong Yang, a senior faculty scientist in Berkeley Lab's Materials Sciences and Chemical Sciences Divisions who led the study. Yang is also a professor of chemistry and materials science and engineering at UC Berkeley. "Knowing how copper is such an excellent electrocatalyst brings us steps closer to turning CO2 into new, renewable solar fuels through artificial photosynthesis."

The work was made possible by combining a new imaging technique called operando 4D electrochemical liquid-cell STEM (scanning transmission electron microscopy) with a soft X-ray probe to investigate the same sample environment: copper nanoparticles in liquid. First author Yao Yang, a UC Berkeley Miller postdoctoral fellow, conceived the groundbreaking approach under the guidance of Peidong Yang while working toward his Ph.D. in chemistry at Cornell University.

Scientists who study artificial photosynthesis materials and reactions have wanted to combine the power of an electron probe with X-rays, but the two techniques typically can't be performed by the same instrument.

Electron microscopes (such as STEM or TEM) use beams of electrons and excel at characterizing the atomic structure in parts of a material. In recent years, 4D STEM (or "2D raster of 2D diffraction patterns using scanning transmission electron microscopy") instruments, such as those at Berkeley Lab's Molecular Foundry, have pushed the boundaries of electron microscopy even further, enabling scientists to map out atomic or molecular regions in a variety of materials, from hard metallic glass to soft, flexible films.

On the other hand, soft (or lower-energy) X-rays are useful for identifying and tracking chemical reactions in real time in an operando, or real-world, environment.

But now, scientists can have the best of both worlds. At the heart of the new technique is an electrochemical "liquid cell" sample holder with remarkable versatility. A thousand times thinner than a human hair, the device is compatible with both STEM and X-ray instruments.

The electrochemical liquid cell's ultrathin design allows reliable imaging of delicate samples while protecting them from electron beam damage. A special electrode custom-designed by co-author Cheng Wang, a staff scientist at Berkeley Lab's Advanced Light Source, enabled the team to conduct X-ray experiments with the electrochemical liquid cell. Combining the two allows researchers to comprehensively characterize electrochemical reactions in real time and at the nanoscale.

Getting granular

During 4D-STEM experiments, Yao Yang and team used the new electrochemical liquid cell to observe copper nanoparticles (ranging in size from 7 nanometers to 18 nanometers) evolve into active nanograins during CO2 electrolysis -- a process that uses electricity to drive a reaction on the surface of an electrocatalyst.

The experiments revealed a surprise: copper nanoparticles combined into larger metallic copper "nanograins" within seconds of the electrochemical reaction.

To learn more, the team turned to Wang, who pioneered a technique known as "resonant soft X-ray scattering (RSoXS) for soft materials," at the Advanced Light Source more than 10 years ago.

With help from Wang, the research team used the same electrochemical liquid cell, but this time during RSoXS experiments, to determine whether copper nanograins facilitate CO2 reduction. Soft X-rays are ideal for studying how copper electrocatalysts evolve during CO2 reduction, Wang explained. By using RSoXS, researchers can monitor multiple reactions between thousands of nanoparticles in real time, and accurately identify chemical reactants and products.

The RSoXS experiments at the Advanced Light Source -- along with additional evidence gathered at Cornell High Energy Synchrotron Source (CHESS) -- proved that metallic copper nanograins serve as active sites for CO2 reduction. (Metallic copper, also known as copper(0), is a form of the element copper.)

During CO2 electrolysis, the copper nanoparticles change their structure during a process called "electrochemical scrambling." The copper nanoparticles' surface layer of oxide degrades, creating open sites on the copper surface for CO2 molecules to attach, explained Peidong Yang. And as CO2 "docks" or binds to the copper nanograin surface, electrons are then transferred to CO2, causing a reaction that simultaneously produces ethylene, ethanol, and propanol along with other multicarbon products.

"The copper nanograins essentially turn into little chemical manufacturing factories," Yao Yang said.

Further experiments at the Molecular Foundry, the Advanced Light Source, and CHESS revealed that size matters. All of the 7-nanometer copper nanoparticles participated in CO2 reduction, whereas the larger nanoparticles did not. In addition, the team learned that only metallic copper can efficiently reduce CO2 into multicarbon products. The findings have implications for "rationally designing efficient CO2 electrocatalysts," Peidong Yang said.

The new study also validated Peidong Yang's findings from 2017: That the 7-nanometer-sized copper nanoparticles require low inputs of energy to start CO2 reduction. As an electrocatalyst, the 7-nanometer copper nanoparticles required a record-low driving force that is about 300 millivolts less than typical bulk copper electrocatalysts. The best-performing catalysts that produce multicarbon products from CO2 typically operate at high driving force of 1 volt.

The copper nanograins could potentially boost the energy efficiency and productivity of some catalysts designed for artificial photosynthesis, a field of research that aims to produce solar fuels from sunlight, water, and CO2. Currently, researchers within the Department of Energy-funded Liquid Sunlight Alliance (LiSA) plan to use the copper nanograin catalysts in the design of future solar fuel devices.

"The technique's ability to record real-time movies of a chemical process opens up exciting opportunities to study many other electrochemical energy conversion processes. It's a huge breakthrough, and it would not have been possible without Yao and his pioneering work," Peidong Yang said.

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Massive fuel-hungry black holes feed off intergalactic gas

Research led by the University of Southampton has revealed how supermassive black holes (SMBHs) are feeding off gas clouds which reach them by travelling hundreds of thousands of light years from one galaxy to another.

An international team of scientists has shown there is a crucial link between the interaction of neighbouring galaxies and the enormous amount of gas needed to 'fuel' these giant, super-dense, space phenomena. Their findings are due to be published in the journal Nature Astronomy.

A black hole can be created when a star collapses, squeezing matter into a relatively tiny space. This increases the force of gravity to a point where nothing can escape, not even light -- hence the name.

Some black holes are gigantic, with masses millions of times greater than our sun, emitting enormous amounts of energy. These are known as 'supermassive black holes' and exactly how they are formed or gain enough fuel to power themselves is still a mystery.

Astrophysicist and lead researcher from the University of Southampton, Dr Sandra Raimundo, comments: "Supermassive black holes fuel their activity by, in part, the gradual accumulation of gas from the environment around them. Supermassive black holes can make the centres of galaxies shine very brightly when they capture gas and it's thought this process can be a major influence on the way that galaxies look today. How SMBHs get enough fuel to sustain their activity and growth still puzzles astronomers, but the work we have carried out provides a step towards understanding this."

The Southampton scientist, working with researchers at the universities of Copenhagen and California, used data from the 4-metre Anglo-Australian telescope in New South Wales, Australia* to study the orbits of gas and stars in a large sample of more than 3000 galaxies. They identified those with the presence of what is known as 'misaligned' gas -- in other words, gas which rotates in a different direction from the stars in the galaxy, signalling a past galaxy interaction. They then found that galaxies with misaligned gas had a higher fraction of active supermassive black holes.

The results showed a clear link between misaligned gas and supermassive black hole activity -- suggesting the gas is transferred where two galaxies meet, meanders vast distances through space and then succumbs to the huge gravitational forces of the supermassive black hole -- pulled in and swallowed up as a vital source of fuel. Astronomers have long suspected that a merger with another galaxy could provide this source of gas, but direct evidence for this has been elusive.

Dr Raimundo explains: "The work that we carried out shows the presence of gas that is misaligned from stars is associated with an increase in the fraction of active supermassive black holes. Since misaligned gas is a clear sign of a past interaction between two galaxies, our work shows that galaxy interactions provide fuel to power active supermassive black holes.

"This is the first time that a direct connection has been observed between the formation and presence of misaligned gas and the fuelling of active supermassive black holes."

Dr Marianne Vestergaard, a co-author in the study, highlights: "What is exciting about these observations is that we can now, for the very first time, identify the captured gas and trace it all the way to the centre where the black hole is devouring it."

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Solar-powered system converts plastic and greenhouse gases into sustainable fuels

Researchers have developed a system that can transform plastic waste and greenhouse gases into sustainable fuels and other valuable products -- using just the energy from the Sun.

The researchers, from the University of Cambridge, developed the system, which can convert two waste streams into two chemical products at the same time -- the first time this has been achieved in a solar-powered reactor.

The reactor converts the carbon dioxide (CO2) and plastics into different products that are useful in a range of industries. 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. The system can easily be tuned to produce different products by changing the type of catalyst used in the reactor.

Converting plastics and greenhouse gases -- two of the biggest threats facing the natural world -- into useful and valuable products using solar energy is an important step in the transition to a more sustainable, circular economy. The results are reported in the journal Nature Synthesis.

"Converting waste into something useful using solar energy is a major goal of our research," said Professor Erwin Reisner from the Yusuf Hamied Department of Chemistry, 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.

Other solar-powered 'recycling' technologies hold promise for addressing plastic pollution and for reducing the amount of greenhouse gases in the atmosphere, but to date, they have not been combined in 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," said Subhajit Bhattacharjee, the paper's co-first author.

"We also need something that's tuneable, so that you can easily make changes depending on the final product you want," said co-first author Dr Motiar Rahaman.

The researchers developed an integrated reactor with two separate compartments: one for plastic, and one for greenhouse gases. The reactor uses a light absorber based on perovskite -- a promising alternative to silicon for next-generation solar cells.

The team designed different catalysts, which were integrated into the light absorber. By changing the catalyst, the researchers could then change the end product. Tests of the reactor under normal temperature and pressure conditions showed that the reactor could efficiently convert PET plastic bottles and CO2 into different carbon-based fuels such as CO, syngas or formate, in addition to glycolic acid. The Cambridge-developed reactor produced these products at a rate that is also 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," said 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," said Bhattacharjee.

Reisner recently received new funding from the European Research Council to help the development of their solar-powered reactor. Over the next five years, they hope to further develop the reactor to produce more complex molecules. The researchers say that similar techniques could someday be used to develop an entirely solar-powered recycling plant.

"Developing a circular economy, where we make useful things 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," said Reisner. "And powering these solutions using the Sun means that we're doing it cleanly and sustainably."

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Floating 'artificial leaves' ride the wave of clean fuel production

Researchers have developed floating 'artificial leaves' that generate clean fuels from sunlight and water, and could eventually operate on a large scale at sea.

The researchers, from the University of Cambridge, designed ultra-thin, flexible devices, which take their inspiration from photosynthesis -- the process by which plants convert sunlight into food. Since the low-cost, autonomous devices are light enough to float, they could be used to generate a sustainable alternative to petrol without taking up space on land.

Outdoor tests of the lightweight leaves on the River Cam -- near iconic Cambridge sites including the Bridge of Sighs, the Wren Library and King's College Chapel -- showed that they can convert sunlight into fuels as efficiently as plant leaves.

This is the first time that clean fuel has been generated on water, and if scaled up, the artificial leaves could be used on polluted waterways, in ports or even at sea, and could help reduce the global shipping industry's reliance on fossil fuels. The results are reported in the journal Nature.

While renewable energy technologies, such as wind and solar, have become significantly cheaper and more available in recent years, for industries such as shipping, decarbonisation is a much taller order. Around 80% of global trade is transported by cargo vessels powered by fossil fuels, yet the sector has received remarkably little attention in discussions around the climate crisis.

For several years, Professor Erwin Reisner's research group in Cambridge has been working to address this problem by developing sustainable solutions to petrol which are based on the principles of photosynthesis. In 2019, they developed an artificial leaf, which makes syngas -- a key intermediate in the production of many chemicals and pharmaceuticals -- from sunlight, carbon dioxide and water.

The earlier prototype generated fuel by combining two light absorbers with suitable catalysts. However, it incorporated thick glass substrates and moisture protective coatings, which made the device bulky.

"Artificial leaves could substantially lower the cost of sustainable fuel production, but since they're both heavy and fragile, they're difficult to produce at scale and transport," said Dr Virgil Andrei from Cambridge's Yusuf Hamied Department of Chemistry, the paper's co-lead author.

"We wanted to see how far we can trim down the materials these devices use, while not affecting their performance," said Reisner, who led the research. "If we can trim the materials down far enough that they're light enough to float, then it opens up whole new ways that these artificial leaves could be used."

For the new version of the artificial leaf, the researchers took their inspiration from the electronics industry, where miniaturisation techniques have led to the creation of smartphones and flexible displays, revolutionising the field.

The challenge for the Cambridge researchers was how to deposit light absorbers onto lightweight substrates and protect them against water infiltration. To overcome these challenges, the team thin-film metal oxides and materials known as perovskites, which can be coated onto flexible plastic and metal foils. The devices were covered with micrometre thin, water-repellent carbon-based layers that prevented moisture degradation. They ended up with a device that not only works, but also looks like a real leaf.

"This study demonstrates that artificial leaves are compatible with modern fabrication techniques, representing an early step towards the automation and up-scaling of solar fuel production," said Andrei. "These leaves combine the advantages of most solar fuel technologies, as they achieve the low weight of powder suspensions and the high performance of wired systems."

Tests of the new artificial leaves showed that they can split water into hydrogen and oxygen, or reduce CO2 to syngas. While additional improvements will need to be made before they are ready for commercial applications, the researchers say this development opens whole new avenues in their work.

"Solar farms have become popular for electricity production; we envision similar farms for fuel synthesis," said Andrei. "These could supply coastal settlements, remote islands, cover industrial ponds, or avoid water evaporation from irrigation canals."

"Many renewable energy technologies, including solar fuel technologies, can take up large amounts of space on land, so moving production to open water would mean that clean energy and land use aren't competing with one another," said Reisner. "In theory, you could roll up these devices and put them almost anywhere, in almost any country, which would also help with energy security."

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Lunar soil has the potential to generate oxygen and fuel

Soil on the moon contains active compounds that can convert carbon dioxide into oxygen and fuels, scientists in China report May 5 in the journal Joule. They are now exploring whether lunar resources can be used to facilitate human exploration on the moon or beyond.

Nanjing University material scientists Yingfang Yao and Zhigang Zou hope to design a system that takes advantage of lunar soil and solar radiation, the two most abundant resources on the moon. After analyzing the lunar soil brought back by China's Chang'e 5 spacecraft, their team found the sample contains compounds -- including iron-rich and titanium-rich substances -- that could work as a catalyst to make desired products such as oxygen using sunlight and carbon dioxide.

Based on the observation, the team proposed an "extraterrestrial photosynthesis" strategy. Mainly, the system uses lunar soil to electrolyze water extracted from the moon and in astronauts' breathing exhaust into oxygen and hydrogen powered by sunlight. The carbon dioxide exhaled by moon inhabitants is also collected and combined with hydrogen from water electrolysis during a hydrogenation process catalyzed by lunar soil.

The process yields hydrocarbons such as methane, which could be used as fuel. The strategy uses no external energy but sunlight to produce a variety of desirable products such as water, oxygen, and fuel that could support life on a moonbase, the researchers say. The team is looking for an opportunity to test the system in space, likely with China's future crewed lunar missions.

"We use in-situ environmental resources to minimize rocket payload, and our strategy provides a scenario for a sustainable and affordable extraterrestrial living environment," Yao says.

While the catalytic efficiency of lunar soil is less than catalysts available on Earth, Yao says the team is testing different approaches to improve the design, such as melting the lunar soil into a nanostructured high-entropy material, which is a better catalyst.

Previously, scientists have proposed many strategies for extraterrestrial survival. But most designs require energy sources from Earth. For example, NASA's Perseverance Mars rover brought an instrument that can use carbon dioxide in the planet's atmosphere to make oxygen, but it's powered by a nuclear battery onboard.

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Scientists find elusive gas from post-starburst galaxies hiding in plain sight

Post-starburst galaxies were previously thought to scatter all of their gas and dust -- the fuel required for creating new stars -- in violent bursts of energy, and with extraordinary speed. Now, new data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveals that these galaxies don't scatter all of their star-forming fuel after all. Instead, after their supposed end, these dormant galaxies hold onto and compress large amounts of highly-concentrated, turbulent gas. But contrary to expectation, they're not using it to form stars.

In most galaxies, scientists expect gas to be distributed in a way similar to starlight. But for post-starburst galaxies, or PSBs, this isn't the case. PSBs are different from other galaxies because they are born in the aftermath of violent collisions, or mergers between galaxies. Galaxy mergers typically trigger massive bursts of star formation, but in PSBs, this outburst slows down and near-completely stops almost as soon as it begins. As a result, scientists previously believed that little or no star-forming fuel was left in these galaxies' central star-forming factories. And until now, the belief was that the molecular gases had been redistributed to radii well beyond the galaxies, either through stellar processes or by the effects of black holes. The new results challenge this theory.

"We've known for some time that large amounts of molecular gas remains in the vicinity of PSBs but haven't been able to say where, which in turn, has prevented us from understanding why these galaxies stopped forming stars. Now, we have discovered a considerable amount of remaining gas within the galaxies and that remaining gas is very compact," said Adam Smercina, an astronomer at the University of Washington and the principal investigator of the study. "While this compact gas should be forming stars efficiently, it isn't. In fact, it is less than 10-percent as efficient as similarly compact gas is expected to be."

In addition to being compact enough to make stars, the gas in the observed dormant -- or quiescent -- galaxies had another surprise in store for the team: it was often centrally-located, though not always, and was surprisingly turbulent. Combined, these two characteristics led to more questions than answers for researchers.

"The rates of star formation in the PSBs we observed are much lower than in other galaxies, even though there appears to be plenty of fuel to sustain the process," said Smercina. "In this case, star formation may be suppressed due to turbulence in the gas, much like a strong wind can suppress a fire. However, star formation can also be enhanced by turbulence, just like wind can fan flames, so understanding what is generating this turbulent energy, and how exactly it is contributing to dormancy, is a remaining question of this work."

Decker French, an astronomer at the University of Illinois, and a co-author of the research added, "These results raise the question of what energy sources are present in these galaxies to drive turbulence and prevent the gas from forming new stars. One possibility is energy from the accretion disk of the central supermassive black holes in these galaxies."

A clear understanding of the processes that govern the formation of stars and galaxies is key to providing context to the Universe and our place in it. The discovery of turbulent, compact gas in otherwise dormant galaxies gives researchers one more clue to solving the mystery of how galaxies in particular live, evolve and die over the course of billions of years. And that means additional future research with the help of ALMA's 1.3mm receiver, which sees the otherwise invisible with stark clarity.

J.D. Smith, an astronomer at the University of Toledo, and a co-author of the research said, "There is much about the evolution of a typical galaxy we don't understand, and the transition from their vibrant star-forming lives into quiescence is one of the least understood periods. Although post-starbursts were very common in the early Universe, today they are quite rare. This means the nearest examples are still hundreds of millions of light-years away, but these events foreshadow the potential outcome of a collision, or merger, between the Milky Way Galaxy and the Andromeda Galaxy several billion years from now. Only with the incredible resolving power of ALMA could we peer deep into the molecular reservoirs left behind 'after the fall.'"

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Carbon dioxide reactor makes 'Martian fuel'

Engineers at the University of Cincinnati are developing new ways to convert greenhouse gases to fuel to address climate change and get astronauts home from Mars.

UC College of Engineering and Applied Science assistant professor Jingjie Wu and his students used a carbon catalyst in a reactor to convert carbon dioxide into methane. Known as the "Sabatier reaction" from the late French chemist Paul Sabatier, it's a process the International Space Station uses to scrub the carbon dioxide from air the astronauts breathe and generate rocket fuel to keep the station in high orbit.

But Wu is thinking much bigger.

The Martian atmosphere is composed almost entirely of carbon dioxide. Astronauts could save half the fuel they need for a return trip home by making what they need on the red planet once they arrive, Wu said.

"It's like a gas station on Mars. You could easily pump carbon dioxide through this reactor and produce methane for a rocket," Wu said.

UC's study was published in the journal Nature Communications with collaborators from Rice University, Shanghai University and East China University of Science and Technology.

Wu began his career in chemical engineering by studying fuel cells for electric vehicles but began looking at carbon dioxide conversion in his chemical engineering lab about 10 years ago.

"I realized that greenhouse gases were going to be a big issue in society," Wu said. "A lot of countries realized that carbon dioxide is a big issue for the sustainable development of our society. That's why I think we need to achieve carbon neutrality."

The Biden Administration has set a goal of achieving a 50% reduction in greenhouse gas pollutants by 2030 and an economy that relies on renewable energy by 2050.

"That means we'll have to recycle carbon dioxide," Wu said.

Wu and his students, including lead author and UC doctoral candidate Tianyu Zhang, are experimenting with different catalysts such as graphene quantum dots -- layers of carbon just nanometers big -- that can increase the yield of methane.

Wu said the process holds promise to help mitigate climate change. But it also has a big commercial advantage in producing fuel as a byproduct.

"The process is 100 times more productive than it was just 10 years ago. So you can imagine that progress will come faster and faster," Wu said. "In the next 10 years, we'll have a lot of startup companies to commercialize this technique."

Wu's students are using different catalysts to produce not only methane but ethylene. Called the world's most important chemical, ethylene is used in the manufacture of plastics, rubber, synthetic clothing and other products.

"Green energy will be very important. In the future, it will represent a huge market. So I wanted to work on it," Zhang said.

Synthesizing fuel from carbon dioxide becomes even more commercially viable when coupled with renewable energy such as solar or wind power, Wu said.

"Right now we have excess green energy that we just throw away. We can store this excess renewable energy in chemicals," he said.

The process is scalable for use in power plants that can generate tons of carbon dioxide. And it's efficient since the conversion can take place right where excess carbon dioxide is produced.

Wu said advances in fuel production from carbon dioxide make him more confident that humans will set foot on Mars in his lifetime.

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California's diesel emissions rules reduce air pollution, protect vulnerable communities

 Extending California's stringent diesel emissions standards to the rest of the U.S. could dramatically improve the nation's air quality and health, particularly in lower income communities of color, finds a new analysis published today in the journal Science.

Since 1990, California has used its authority under the federal Clean Air Act to enact more aggressive rules on emissions from diesel vehicles and engines compared to the rest of the U.S. These policies, crafted by the California Air Resources Board (CARB), have helped the state reduce diesel emissions by 78% between 1990 and 2014, while diesel emissions in the rest of the U.S. dropped by just 51% during the same time period, the new analysis found.

The study estimates that by 2014, improved air quality cut the annual number of diesel-related cardiopulmonary deaths in the state in half, compared to the number of deaths that would have occurred if California had followed the same trajectory as the rest of the U.S. Adopting similar rules nationwide could produce the same kinds of benefits, particularly for communities that have suffered the worst impacts of air pollution.

"Everybody benefits from cleaner air, but we see time and again that it's predominantly lower income communities of color that are living and working in close proximity to sources of air pollution, like freight yards, highways and ports. When you target these sources, it's the highly exposed communities that stand to benefit most," said study lead author Megan Schwarzman, a physician and environmental health scientist at the University of California, Berkeley's School of Public Health. "It's about time, because these communities have suffered a disproportionate burden of harm."

The study also points out that exposure to fine particulate matter (PM2.5) has been linked to poor outcomes from COVID-19, adding urgency to the need to reduce air pollution, par¬ticularly for communities of color that are disproportionately affected by both.

Diesel exhaust consists of both particles and gases and contributes significantly to PM2.5 air pollution worldwide. PM2.5 exposure from any source can compromise children's lung development and can trigger airway inflammation and exacerbate asthma and cardiopulmonary diseases. Diesel exhaust has also been designated a human carcinogen by California's Office of Environmental Health Hazard Assessment (OEHHA).

"There are hundreds of studies around the world that link particulate matter exposure and premature death," said study co-author Álvaro Alvarado, a former air pollution specialist at CARB who now works for OEHHA. "In cities with higher levels of air pollution, there are also higher hospitalization rates for respiratory and cardiovascular illnesses and more emergency room visits for asthma."

To improve air quality, CARB's policies have gone beyond federal standards to limit diesel emissions from a variety of mobile sources, including heavy-duty trucks and buses, ships and port equipment, train locomotives, and the engines that power construction equipment and agricultural machinery.

In their study, Schwarzman and colleagues catalogued the wide range of CARB policies that target each emissions sector and tracked how changes in diesel emissions corresponded to the implementation of those rules. They then show the impact of CARB policies by comparing California's reductions in diesel emissions to those in the rest of the U.S. Their analysis reveals that CARB's policies reduced emissions to the extent that, by 2014, California was emitting less than half the diesel particulate matter, as would be expected had the state followed the same trajectory as the rest of the U.S.

One key policy approach that sets California apart is the requirement that older diesel engines be retrofitted to meet strict emissions standards, Schwarzman said. In the rest of the U.S., new diesel engines must meet updated emissions standards, but older, dirtier engines are allowed to operate without upgrades.

"The average lifetime of a diesel engine is about 20 years, or a million miles, so waiting for fleet turnover is just too slow," Schwarzman said. "California requires retrofits for existing trucks so that all diesel engines are held to a higher standard. This has made an enormous difference for air quality."

Requiring upgrades for the engines that power heavy-duty trucks and buses has reduced California's diesel emissions in that sector by 85% since 1990, the study found. By comparison, the study estimates that if California's heavy-duty vehicle sector had followed the trajectory of other U.S. states, the sector's emissions would have dropped by only 58% in that period.

Because the highways, ports and rail yards where diesel engines operate are more likely to be located near lower income communities of color than affluent, white communities, regulating diesel emissions can help correct persistent disparities in air quality and health, said senior study author John Balmes, a Berkeley Public Health professor and professor of medicine at the University of California, San Francisco.

"There are truly different levels of exposure to air pollution, and those differences in exposure have been linked to differential health outcomes," said Balmes, who also serves as the physician member of CARB.

The study reports that every dollar the state has spent controlling air pollution has generated $38 in benefits attributable to lower rates of illness, premature death and lost productivity attributable to air pollution. As a result, there is no reason why the U.S. as a whole shouldn't adopt diesel emissions standards similar to California's, the authors argue.

"In terms of public health, federal air quality policy should be moving toward that of California, because we've shown that it works, and we've also shown that greening transportation can be good for economic growth," Balmes said. "These environmental regulations not only save lives and improve public health, they actually drive innovation and grow the green economy, which is the future."

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Wireless device makes clean fuel from sunlight, CO2 and water

 Researchers have developed a standalone device that converts sunlight, carbon dioxide and water into a carbon-neutral fuel, without requiring any additional components or electricity.

The device, developed by a team from the University of Cambridge, is a significant step toward achieving artificial photosynthesis -- a process mimicking the ability of plants to convert sunlight into energy. It is based on an advanced 'photosheet' technology and converts sunlight, carbon dioxide and water into oxygen and formic acid -- a storable fuel that can be either be used directly or be converted into hydrogen.

The results, reported in the journal Nature Energy, represent a new method for the conversion of carbon dioxide into clean fuels. The wireless device could be scaled up and used on energy 'farms' similar to solar farms, producing clean fuel using sunlight and water.

Harvesting solar energy to convert carbon dioxide into fuel is a promising way to reduce carbon emissions and transition away from fossil fuels. However, it is challenging to produce these clean fuels without unwanted by-products.

"It's been difficult to achieve artificial photosynthesis with a high degree of selectivity, so that you're converting as much of the sunlight as possible into the fuel you want, rather than be left with a lot of waste," said first author Dr Qian Wang from Cambridge's Department of Chemistry.

"In addition, storage of gaseous fuels and separation of by-products can be complicated -- we want to get to the point where we can cleanly produce a liquid fuel that can also be easily stored and transported," said Professor Erwin Reisner, the paper's senior author.

In 2019, researchers from Reisner's group developed a solar reactor based on an 'artificial leaf' design, which also uses sunlight, carbon dioxide and water to produce a fuel, known as syngas. The new technology looks and behaves quite similarly to the artificial leaf but works in a different way and produces formic acid.

While the artificial leaf used components from solar cells, the new device doesn't require these components and relies solely on photocatalysts embedded on a sheet to produce a so-called photocatalyst sheet. The sheets are made up of semiconductor powders, which can be prepared in large quantities easily and cost-effectively.

In addition, this new technology is more robust and produces clean fuel that is easier to store and shows potential for producing fuel products at scale. The test unit is 20 square centimetres in size, but the researchers say that it should be relatively straightforward to scale it up to several square metres. In addition, the formic acid can be accumulated in solution, and be chemically converted into different types of fuel.

"We were surprised how well it worked in terms of its selectivity -- it produced almost no by-products," said Wang. "Sometimes things don't work as well as you expected, but this was a rare case where it actually worked better."

The carbon-dioxide converting cobalt-based catalyst is easy to make and relatively stable. While this technology will be easier to scale up than the artificial leaf, the efficiencies still need to be improved before any commercial deployment can be considered. The researchers are experimenting with a range of different catalysts to improve both stability and efficiency.

The current results were obtained in collaboration with the team of Professor Kazunari Domen from the University of Tokyo, a co-author of the study.

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New catalyst efficiently turns carbon dioxide into useful fuels and chemicals

 As levels of atmospheric carbon dioxide continue to climb, scientists are looking for new ways of breaking down CO2 molecules to make useful carbon-based fuels, chemicals and other products. Now, a team of Brown University researchers has found a way to fine-tune a copper catalyst to produce complex hydrocarbons -- known as C2-plus products -- from CO2 with remarkable efficiency.

In a study published in Nature Communications, the researchers report a catalyst that can produce C2-plus compounds with up to 72% faradaic efficiency (a measure of how efficiently electrical energy is used to convert carbon dioxide into chemical reaction products). That's far better than the reported efficiencies of other catalysts for C2-plus reactions, the researchers say. And the preparation process can be scaled up to an industrial level fairly easily, which gives the new catalyst potential for use in large-scale CO2 recycling efforts.

"There had been reports in the literature of all kinds of different treatments for copper that could produce these C2-plus with a range of different efficiencies," said Tayhas Palmore, the a professor of engineering at Brown who co-authored the paper with Ph.D. student Taehee Kim. "What Taehee did was a set of experiments to unravel what each of these treatment steps was actually doing to the catalyst in terms of reactivity, which pointed the way to optimizing a catalyst for these multi-carbon compounds."

There have been great strides in recent years in developing copper catalysts that could make single-carbon molecules, Palmore says. For example, Palmore and her team at Brown recently developed a copper foam catalyst that can produce formic acid efficiently, an important single-carbon commodity chemical. But interest is increasing in reactions that can produce C2-plus products.

"Ultimately, everyone seeks to increase the number of carbons in the product to the point of producing higher carbon fuels and chemicals," Palmore said.

There had been evidence from prior research that halogenation of copper -- a reaction that coats a copper surface with atoms of chlorine, bromine or iodine in the presence of an electrical potential -- could increase a catalyst's selectivity of C2-plus products. Kim experimented with a variety of different halogenation methods, zeroing in on which halogen elements and which electrical potentials yielded catalysts with the best performance in CO2-to-C2-plus reactions. He found that the optimal preparations could yield faradaic efficiencies of between 70.7% and 72.6%, far higher than any other copper catalyst.

The research helps to reveal the attributes that make a copper catalyst good for C2-plus products. The preparations with the highest efficiencies had a large number of surface defects -- tiny cracks and crevices in the halogenated surface -- that are critical for carbon-carbon coupling reactions. These defect sites appear to be key to the catalysts' high selectivity toward ethylene, a C2-plus product that can be polymerized and used to make plastics.

Ultimately, such a catalyst will aid in large-scale recycling of CO2. The idea is to capture CO2 produced by industrial facilities like power plants, cement manufacturing or directly from air, and convert it into other useful carbon compounds. That requires an efficient catalyst that is easy to produce and regenerate, and inexpensive enough to operate on an industrial scale. This new catalyst is a promising candidate, the researchers say.

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Scientists create 'artificial leaf' that turns carbon into fuel

Scientists have created an "artificial leaf" to fight climate change by inexpensively converting harmful carbon dioxide (CO2) into a useful alternative fuel.

The new technology, outlined in a paper published today in the journal Nature Energy, was inspired by the way plants use energy from sunlight to turn carbon dioxide into food.

"We call it an artificial leaf because it mimics real leaves and the process of photosynthesis," said Yimin Wu, an engineering professor at the University of Waterloo who led the research. "A leaf produces glucose and oxygen. We produce methanol and oxygen."

Making methanol from carbon dioxide, the primary contributor to global warming, would both reduce greenhouse gas emissions and provide a substitute for the fossil fuels that create them.

The key to the process is a cheap, optimized red powder called cuprous oxide.

Engineered to have as many eight-sided particles as possible, the powder is created by a chemical reaction when four substances -- glucose, copper acetate, sodium hydroxide and sodium dodecyl sulfate -- are added to water that has been heated to a particular temperature.

The powder then serves as the catalyst, or trigger, for another chemical reaction when it is mixed with water into which carbon dioxide is blown and a beam of white light is directed with a solar simulator.

"This is the chemical reaction that we discovered," said Wu, who has worked on the project since 2015. "Nobody has done this before."

The reaction produces oxygen, as in photosynthesis, while also converting carbon dioxide in the water-powder solution into methanol. The methanol is collected as it evaporates when the solution is heated.

Next steps in the research include increasing the methanol yield and commercializing the patented process to convert carbon dioxide collected from major greenhouse gas sources such as power plants, vehicles and oil drilling.

"I'm extremely excited about the potential of this discovery to change the game," said Wu, a professor of mechanical and mechatronics engineering, and a member of the Waterloo Institute for Nanotechnology. "Climate change is an urgent problem and we can help reduce CO2 emissions while also creating an alternative fuel."

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