The Future of Solar Technology: New Technology Makes Foldable Cells a Practical Reality (Material Science)

International research team creates solar cells with unprecedented flexibility and resistance

With the recent development of foldable mobile phone screens, research on foldable electronics has never been so intensive. One particularly useful application of the foldable technology is in solar panels.

Current solar cells are restricted to rigid, flat panels, which are difficult to store in large numbers and integrate into everyday appliances, including phones, windows, vehicles, or indoor devices. But, one problem prevents this formidable technology from breaking through: to be integrated into these items, solar cells need to be foldable, to bend at will repeatedly without breaking. Traditional conducting materials used in solar cells lack flexibility, creating a huge obstacle in developing fully foldable cells.

A key requirement for an efficient foldable conductor is the ability to withstand the pressure of bending within a very small radius while maintaining its integrity and other desirable properties. In short, a thin, flexible, transparent, and resilient conductor material is needed. Professor Il Jeon of Pusan National University, Korea, elaborates, “Unlike merely flexible electronics, foldable devices are subject to much harsher deformations, with folding radii as small as 0.5 mm. This is not possible with conventional ultra-thin glass substrates and metal oxide transparent conductors, which can be made flexible but never fully foldable.

Fortunately, an international team of researchers, including Prof. Jeon, have found a solution, in a study published in Advanced Science. They identified a promising candidate to answer all of these requirements: single-walled carbon nanotube (SWNT) films, owing to their high transparency and mechanical resilience. The only problem is that SWNTs struggle to adhere to the substrate surface when force is applied (such as bending) and requires chemical doping. To address this problem, the scientists embedded the conducting layer into a polyimide (PI) substrate, filling the void spaces in the nanotubes.

To ensure maximum performance, they also “doped” the resulting material to increase its conductivity. By introducing small impurities (in this case, withdrawn electrons to molybdenum oxide) into the SWNT-PI nanocomposite layer, the energy needed for electrons to move across the structure is much smaller, and hence more charge can be generated for a given amount of current.

Their resulting prototype far exceeded the team’s expectations. Only 7 micrometers thick, the composite film exhibited exceptional resistance to bending, almost 80% transparency, and a power conversion efficiency of 15.2%, the most ever achieved in solar cells using carbon nanotube conductors! In fact, as pointed out by Prof. Jeon, “The obtained results are some of the best among those reported thus far for flexible solar cells, both in terms efficiency and mechanical stability.

With this novel breakthrough in solar harvesting technology, one can only imagine what next-generation solar panels will look like.

Featured image: Foldable Perovskite Solar Cells Using Carbon Nanotube-Embedded Ultrathin Polyimide Conductor © Pusan National University


Reference: Yoon, J., Kim, U., Yoo, Y., Byeon, J., Lee, S.‐K., Nam, J.‐S., Kim, K., Zhang, Q., Kauppinen, E. I., Maruyama, S., Lee, P., Jeon, I., Foldable Perovskite Solar Cells Using Carbon Nanotube‐Embedded Ultrathin Polyimide Conductor. Adv. Sci. 2021, 2004092. https://doi.org/10.1002/advs.202004092 https://onlinelibrary.wiley.com/doi/10.1002/advs.202004092


Provided by Pusan National University

A Novel Approach To Determine How Carcinogenic Bacteria Find Their Targets (Medicine)

Treatments targeting the motility system of the bacteria could eliminate the risk of antibiotic resistance.

The gram-negative bacteria Helicobacter pylori (H. pylori) colonize the stomachs of the majority of the world’s population. Although most people may never experience major complications due to the pathogen, H. pylori infections increase the risk of certain types of gastric cancer, as well as other illnesses such as peptic ulcers and gastritis.

Currently, H. pylori infections are treatable with a cocktail of antibiotics, but the rapid emergence of antibiotic resistance in H. pylori is a significant concern. To counter these threats, Pushkar Lele, assistant professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M University, investigated how H. pylori locate their ideal environment within a host’s stomach.

Motile bacteria such as H. pylori swim by rotating string-like appendages called flagella. They navigate by sensing chemical signals in their environment, a process known as chemotaxis. An intracellular signaling pathway – the chemotaxis network – aids navigation by controlling the direction of rotation of the flagella. Current understanding of how the chemotaxis network operates is based on studies of Escherichia coli (E. coli), which is a model system for bacterial chemotaxis and motility. The chemotaxis network in E. coli modulates the probability of clockwise rotation in otherwise counterclockwise-rotating flagella to help the cell migrate toward favorable chemical environments. How the chemotaxis network modulates flagellar functions in H. pylori is not known.

Popular techniques that use probes to study chemotactic function in bacteria do not work well in H. pylori. This creates significant challenges in understanding flagellar functions in this species. To overcome these challenges, Lele’s group pioneered a novel probe-free approach to study flagellar functions in H. pylori.

Their approach exploited the fact that cells swam around in clockwise circles near glass surfaces when their flagella rotated counterclockwise, and counterclockwise circles when their flagella rotated clockwise. In a paper published in eLife, Lele and his research team used this approach to report the probability of the clockwise rotation in H. pylori for the first time. Jyot Antani, a doctoral student in Lele’s group, performed the experiments that further showed that H. pylori’s chemotaxis network modulates flagellar functions similar to that in E. coli.

Lele said the similarity in the form of flagellar control in the two bacterial species is intriguing given that they differ in many key aspects. Whereas H. coli prefer the stomach, E. coli are found in the lower gastrointestinal tract. The physical characteristics of H. pylori are such that they run forward and reverse, unlike E. coli, which run forward and then tumble. As a result, the modulation of the probabilities of clockwise flagellar rotation, which suits E. coli very well, is predicted to cause errors in chemotaxis in H. pylori.

Lele predicts that future work with their new approach will reveal how H. pylori reach their targets despite the errors and how dietary interventions can be developed to inhibit chemotaxis.

This research was supported by a High Impact High Risk Awards grant from the Cancer Prevention and Research Institute of Texas.

Featured image: An artist’s representation of Helicobacter pylori, a carcinogen that can lead to certain types of cancer. © Getty Images


Reference: Jyot D Antani, Anita X Sumali, Tanmay P Lele, Pushkar P Lele, “Asymmetric random walks reveal that the chemotaxis network modulates flagellar rotational bias in Helicobacter pylori”, ELife, 2021. DOI: 10.7554/eLife.63936 https://elifesciences.org/articles/63936


Provided by Texas A&M University College of Engineering

How The 3-D Structure Of Eye-lens Proteins is Formed? (Biology)

Chemical bonds within the eye-lens protein gamma-B crystallin hold the protein together and are therefore important for the function of the protein within the lens. Contrary to previous assumptions, some of these bonds, called disulphide bridges, are already formed simultaneously with the synthesis of the protein in the cell. This is what scientists at Goethe University Frankfurt, Max Planck Institute of Biophysics  and the French Institute de Biologie Structurale in Grenoble have discovered.

The lens of the human eye gets its transparency and refractive power from the fact that certain proteins are densely packed in its cells. These are mainly crystallines. If this dense packing cannot be maintained, for example due to hereditary changes in the crystallines, the result is lens opacities, known as cataracts, which are the most common cause of vision loss worldwide.

In order for crystallins to be packed tightly in lens fibre cells, they must be folded stably and correctly. Protein folding already begins during the biosynthesis of proteins in the ribosomes, which are large protein complexes. Ribosomes help translate the genetic code into a sequence of amino acids. In the process, ribosomes form a protective tunnel around the new amino acid chain, which takes on three-dimensional structures with different elements such as helices or folded structures immediately after the tunnel’s formation. The gamma-B crystallines studied in Frankfurt and Grenoble also exhibit many bonds between two sulphur-containing amino acids, so-called disulphide bridges.

The production of these disulphide bridges is not easy for the cell, since biochemical conditions prevail in the cell environment that prevent or dissolve such disulphide bridges. In the finished gamma-B crystalline protein, the disulphide bridges are therefore shielded from the outside by other parts of the protein. However, as long as the protein is in the process of formation, this is not yet possible.

But because the ribosomal tunnel was considered too narrow, it was assumed – also on the basis of other studies – that the disulphide bridges of the gamma-B crystallins are formed only after the proteins have been completed. To test this assumption, the researchers from Frankfurt and Grenoble used genetically modified bacterial cells as a model system, stopped the synthesis of the gamma-B crystallins at different points in time and examined the intermediate products with mass spectrometric, nuclear magnetic resonance spectroscopic and electron microscopic methods, and supplemented these with theoretical simulation calculations. The result: The disulphide bridges are already formed on the not yet finished protein during the synthesis of the amino acid chain.

„We were thus able to show that disulphide bridges can already form in the ribosomal tunnel, which offers sufficient space for this and shields the disulphide bridges from the cellular milieu,“ says Prof. Harald Schwalbe from the Institute of Organic Chemistry and Chemical Biology at Goethe University. „Surprisingly, however, these are not the same disulphide bridges that are later present in the finished gamma-B crystallin. We conclude that at least some of the disulphide bridges are later dissolved again and linked differently. The reason for this probably lies in the optimal timing of protein production: the ‚preliminary‘ disulphide bridges accelerate the formation of the ‚final‘ disulphide bridges when the gamma-B crystallin is released from the ribosome.“

In further studies, the researchers now want to test whether the synthesis processes in the slightly different ribosomes of higher cells are similar to those in the bacterial model system.

Featured image: In cells, ribosomes (blue and yellow) move along mRNA molecules (red „string“) and produce proteins which are depicted here as violett strings. ©GUF


Reference: Linda Schulte, Jiafei Mao, Julian Reitz, Sridhar Sreeramulu, Denis Kudlinzki, Victor-Valentin Hodirnau, Jakob Meier-Credo, Krishna Saxena, Florian Buhr, Julian D. Langer, Martin Blackledge, Achilleas S. Frangakis, Clemens Glaubitz, Harald Schwalbe: Cysteine oxidation and disulfide formation in the ribosomal exit tunnel. Nature Communications, 2021. https://doi.org/10.1038/s41467-020-19372-x


Provided by Goethe University Frankfrut

Researchers Unravel What Makes Someone a COVID-19 Super-spreader (Medicine)

Scientists and public health experts have long known that certain individuals, termed “super-spreaders,” can transmit COVID-19 with incredible efficiency and devastating consequences. 

Now, researchers at Tulane University, Harvard University, MIT and Massachusetts General Hospital have learned that obesity, age and COVID-19 infection correlate with a propensity to breathe out more respiratory droplets — key spreaders of SARS-CoV-2, the virus that causes COVID-19. Their findings were published in Proceedings of the National Academy of Sciences

Using data from an observational study of 194 healthy people and an experimental study of nonhuman primates with COVID-19, researchers found that exhaled aerosol particles vary greatly between subjects. Those who were older with higher body mass indexes (BMI) and an increasing degree of COVID-19 infection had three times the number of exhaled respiratory droplets as others in the study groups.

Researchers found that 18% of the human subjects accounted for 80% of the exhaled particles of the group, reflecting a distribution of exhaled aerosol particles that follows the 20/80 rule seen in other infectious disease epidemics – meaning 20% of infected individuals are responsible for 80% of transmissions. 

Aerosol droplets in nonhuman primates increased as infection with COVID-19 progressed, reaching peak levels a week after infection before falling to normal after two weeks. Notably, as infection with COVID-19 progressed, viral particles got smaller, reaching the size of a single micron at the peak of infection. Tiny particles are more likely to be expelled as people breathe, talk or cough. They can also stay afloat much longer, travel farther in the air and penetrate deeper into the lungs when inhaled.

The increase in exhaled aerosols occurred even among those with asymptomatic cases of COVID-19, said Chad Roy, PhD, corresponding author and director of infectious disease aerobiology at the Tulane National Primate Research Center.

“We’ve seen a similar increase in droplets during the acute infection stage with other infectious diseases like tuberculosis,” Roy said. “It seems likely that viral and bacterial infections of the airway can weaken airway mucus, which promotes the movement of infectious particles into this environment.” 

The generation of respiratory drops in the airways varies between people depending on their body composition, said lead author David Edwards, PhD, professor of the practice of biomedical engineering at Harvard University.

“While our results show that the young and healthy tend to generate far fewer droplets than the older and less healthy, they also show that any of us, when infected by COVID-19, may be at risk of producing a large number of respiratory droplets,” Edwards said.

Featured image: Chad Roy, PhD, corresponding author of the study and director of infectious disease aerobiology at the Tulane National Primate Research Center. © Tulane


Reference: David A. Edwards, Dennis Ausiello, Jonathan Salzman, Tom Devlin, Robert Langer, Brandon J. Beddingfield, Alyssa C. Fears, Lara A. Doyle-Meyers, Rachel K. Redmann, Stephanie Z. Killeen, Nicholas J. Maness, Chad J. Roy, “Exhaled aerosol increases with COVID-19 infection, age, and obesity“, Proceedings of the National Academy of Sciences Feb 2021, 118 (8) e2021830118; DOI: 10.1073/pnas.2021830118


Provided by University of Tulane

A Recipe For Regenerating Bioengineered Hair (Biology)

Researchers at the RIKEN Center for Biosystems Dynamics Research in Japan have discovered a recipe for continuous cyclical regeneration of cultured hair follicles from hair follicle stem cells.

Scientists have been making waves in recent years by developing ways to grow a variety of useful items in laboratories, from meat and diamonds to retinas and other organoids. At the RIKEN Center for Biosystems Dynamics Research in Japan, a team led by Takashi Tsuji has been working on ways to regenerate lost hair from stem cells. In an important step, a new study identifies a population of hair follicle stem cells in the skin and a recipe for normal cyclical regeneration in the lab.

The researchers took fur and whisker cells from mice and cultured them in the laboratory with other biological “ingredients”. They used 220 combinations of ingredients, and found that combining a type of collagen with five factors–the NFFSE medium–led to the highest rate of stem cell amplification in the shortest period of time.

Diagram of a hair follicle taken from back fur. This study found that when Itg-beta5 was present in hair follicle stem cells located in the upper bulge of the follicle, the hair went through many more cycles than when those cells were absent. © RIKEN

Hair growth in mammals is a continuous cyclical process in which hair grows, falls out, and is grown again. Growth occurs in the anagen phase and hair falls out in the telogen phase. Thus, a successful hair-regeneration treatment must produce hair that recycles. To test whether stem cells cultured in the NFFSE medium produce hair that cycles, the researchers placed bioengineered hair follicle stem cells in NFFSE medium or in medium missing one of the ingredients and observed the regenerated hair for several weeks. They found 81% of hair follicles generated in NFFSE medium went through at least three hair cycles and produced normal hair. In contrast, 79% of follicles grown in the other medium produced only one hair cycle.

Knowing that stem-cell renewal can depend on what is attached to the outside of the cells, the researchers next looked for markers on the surface of cells cultured in the NFFSE medium. In addition to the expected CD34 and CD49f markers, they found the best hair cycling was related to the addition of Itgβ5. “We found almost 80% of follicles reached three hair cycles when Itgβ5 was also bioengineered into the hair follicle germ,” explains first author Makoto Takeo. “In contrast, only 13% reached three cycles when it was not present.” Analysis showed that these important cells are naturally located in the upper part of the hair follicle’s bulge region.

“Our culture system establishes a method for cyclical regeneration of hair follicles from hair follicle stem cells,” says Tsuji, “and will help make hair follicle regeneration therapy a reality in the near future.” As preclinical animal-safety tests using these cultured cells were completed in 2019, the next step in the process is clinical trials.

“RIKEN is primarily an institute that does basic research,” explains Tsuji. “And clinical trials usually require outside collaborators. We are therefore looking for a partner company to help develop the clinical applications and welcome donations to promote the R&D.”

Featured image: Top row: Hair regenerated using the NFFSE medium that contains five critical factors. Note the hair cycles 4 times (growth ? falling out ? new growth ? repeat). Bottom row: Hair regenerated on medium missing one of the critical ingredients. Hair only cycled once in this case. © RIKEN


Reference: Takeo, M., Asakawa, K., Toyoshima, Ke. et al. Expansion and characterization of epithelial stem cells with potential for cyclical hair regeneration. Sci Rep 11, 1173 (2021). https://doi.org/10.1038/s41598-020-80624-3


Provided by RIKEN

Russian Scientists Significantly Improved Coal-Burning Efficiency (Chemistry)

Highlights

• New study showed that addition of copper salts decreases the delay time and temperature of the ignition.

• Microexplosions occur at early stages of the coal combustion process with additives.

• The content of unburnt carbon in ash residue was averagely reduced by 3.1 times.

• CO content in the gaseous combustion products was diminished by 40%.

• The CO-formation peak is shifted into earlier stages of combustion due to additives.


A team of Russian scientists from NUST MISIS, Tomsk Polytechnic University (TPU) and Boreskov Institute of Catalysis has suggested a new approach to modifying the combustion behavior of coal. The addition of copper salts reduces the content of unburnt carbon in ash residue by 3.1 times and CO content in the gaseous combustion products by 40%, the scientists found. The research was published in Fuel Processing Technology.

According to the International Energy Agency (IEA), coal is the predominant energy resource used as the primary fuel for power generation. According to reports, coal supplied over one-third of global electricity generation in 2020. Experts believe that despite the generally accepted energy policy aimed at reducing the share of coal usage and switching to renewable energy sources, coal, as the main type of fuel in the world, will most likely still occupy a leading position in power generation in the coming years. However, the widespread use of coal is limited by a number of problems, such as incomplete combustion of fuel and concomitant formation of toxic gases. Taking this into account, development of technologies aiming at more effective and environmentally friendly coal thermal conversion is a priority task for the coal-fired power generation industry. One of the possible solutions to improve the coal-burning efficiency is the use of catalytically active agents, such as oxides of various metals and their precursors (salts based on nitrates, sulfates, acetates, and carbonates), to intensify the combustion process.

“It is too early to give up on coal. China, for instance, relies on coal as the primary energy source for much of the 21st century despite all the ‘green’ trends. In Russia, coal accounts for a little under 20% of the country’s energy balance. Even in Great Britain, the country that’s been consistently implementing its decarbonisation policy, the demand for coal by electricity generators was registered at over 200 thousand tons in the third quarter of 2020. It is safe to say that the search for catalytic additives for improved coal-burning efficiency will continue. For us, the search has been quite successful: the use of the additives proposed by our team has been proven to significantly improve coal-burning efficiency, especially with high-ash coals,” noted Alexander Gromov, the NUST MISIS team lead and head of MISIS Catalysis Lab.

The method of coal combustion activation by metal salts is based on intensification of the combustion process and reduction of the combustion temperature. The use of the salt-based additives makes the combustion more manageable, the researchers note.

In their experiments, the scientists used copper salts as activating additives to improve reactivity of the high-ash coal fuels, such as anthracite, also known as hard coal, and semicoke. High-ash fuels are characterized by high minimum ignition and combustion temperatures, and low combustion intensity. The introduction of copper salts resulted in improved reactivity and higher burn rate of the fuel samples. It is also worth mentioning that the content of unburnt carbon in the ash residue of the modified samples was significantly lower than that in the reference samples.

The introduction of copper nitrates, acetates and sulfates to the fuel samples was carried out by the incipient wetness procedure. Ignition and combustion experiments were then performed in a combustion chamber at temperatures of the heating medium varying from 500 °C to 700 °C.

The mechanism of combustion activation relies on the intensification of the production of gas-phase combustion products at the early stage of volatiles’ release and the generation of micro-explosions to prevent formation of slag layers that would otherwise block oxygen from the fuel.

When using oxide-based additives, dynamic contact between the fuel and the additive has to be ensured, the researchers noted. The use of salts as a catalyzing agent doesn’t require that type of contact, which makes this new method of coal modifying potentially applicable in the energy industry.

The researchers believe that the use of salt-based additives for increasing the efficiency of coal-burning could help improve fuel efficiency in energy production, minimize energy use for preheating power generating equipment and reduce carbon emissions from coal-fired power plants.

Featured image: Alexander Gromov, the NUST MISIS team lead and head of MISIS Catalysis Lab. © Sergey Gnuskov/NUST MISIS


Reference: K.B. Larionov, I.V. Mishakov, K.V. Slyusarskiy, S.A. Tsibulskiy, R.B. Tabakaev, Yu.I. Bauman, A.A. Vedyagin, A.Yu. Nalivaiko, A.A. Gromov, “Combustion of bituminous coal and semicoke with copper salts”, Fuel Processing Technology, Volume 213, 2021, 106706, ISSN 0378-3820,
https://doi.org/10.1016/j.fuproc.2020.106706.
(https://www.sciencedirect.com/science/article/pii/S0378382020309978)


Adult Neurogenesis May Hold Clues For More Effective Treatment Of Alcoholism (Medicine)

New research and analysis examine how alcohol exposure impacts many aspects of neuroplasticity in a special issue of Brain Plasticity

Neuroplasticity, the remarkable ability of the brain to modify and reorganize itself, is affected by or in response to excessive alcohol, whether through individual consumption or exposure in the womb. It is now well accepted that the birth and integration of new neurons continue beyond development and into adulthood. New discoveries and insights on how alcohol impacts this and other plastic processes are discussed in “Alcohol and Neural Plasticity,” a special issue of Brain Plasticity.

“The discovery and evolution of our acceptance of the role of adult neurogenesis in brain structure and function have revolutionized our understanding of the brain’s response to insult, but has also introduced a potential mechanism of recovery in some regions,” explains Guest Editor Kimberly Nixon, PhD, The University of Texas at Austin, College of Pharmacy, Austin, TX, USA.

In models of Fetal Alcohol Spectrum Disorder, earlier research found that gestational exposure to moderate levels of alcohol in mice throughout a period equivalent to the first and second human trimesters profoundly impacted neurogenesis. In a follow up study published in this special issue, lead investigator Lee Anna Cunningham, PhD, Department of Neurosciences, University of New Mexico School of Medicine, Albuquerque, NM, USA, and colleagues examined the functional and structural consequences of prenatal alcohol exposure on adult-generated neurons. They found no direct effects of prenatal alcohol exposure on adult hippocampal neurogenesis in mice housed under standard conditions, but prenatal alcohol exposure impaired the neurogenic response to enriched environment. These mice also performed poorly in a neurogenesis-dependent pattern discrimination task and displayed impaired enrichment-mediated increases in dendrite complexity.

“This study further underscores the impact of moderate gestational alcohol exposure on adult hippocampal plasticity and supports adult hippocampal neurogenesis as a potential therapeutic target to remediate certain neurological outcomes in fetal alcohol syndrome,” notes Dr. Cunningham.

The mechanisms of recovery from adult alcohol use disorder are not clear, although reactive neurogenesis has been observed following alcohol dependence. Dr. Nixon and colleagues studied the role of adult-born neurons in the recovery of hippocampal learning and memory during withdrawal and abstinence from alcohol dependence. They hypothesized that reducing reactive neurogenesis would impair functional recovery. Adult male rats were subjected to a four-day binge alcohol exposure, and then reactive neurogenesis was chemically inhibited. Despite reducing this potential mechanism of hippocampal repair, learning and memory behavior still recovered and were identical to controls.

“Further work is needed to better characterize and differentiate how adult-born neurons contribute to both hippocampal impairments in alcohol misuse but also recovery in abstinence,” Dr. Nixon says.

The special issue also reviews several key issues: the effect of combined alcohol and cocaine exposure on neural stem cells and adult neurogenesis; the neurotoxic effects of binge alcohol consumption, highlighting the scarcity of work on females and the aged; the role of immune activation as a mechanism of alcohol’s effects on synaptic and structural plasticity; and one of the first in-depth discussions of alcohol’s neurophysiological effects on hippocampal excitatory activity during alcohol withdrawal. This activity may underlie the hyperexcitability that is seen in alcohol withdrawal and can be a fatal complication of non-medically supervised “detox” from alcohol.

Also included are a review and data paper on alcohol effects on synaptic mechanisms that underlie the various behavioral deficits that occur with the development of alcohol abuse disorder and a developmental study that offers insight into our understanding of alcohol’s effects at synapses during juvenile development.

“The overarching goal of most of our research programs is to find a potential therapeutic target that could be utilized to develop a drug to treat addiction,” Dr. Nixon observes. “The progress I hope for is that if we can find a novel approach or target within these various plasticity systems, it will be more efficacious in the treatment of alcohol use disorders and more people will seek treatment. That said, much of this work is very novel and translational, but not yet near the drug development stage.”

Featured image: Neural plasticity, the remarkable ability of the brain to modify and reorganize itself at the synapse, circuit and cellular levels is affected by and/or in response to excessive alcohol intake or exposure. Outcomes of alcohol use on either neural or developmental plasticity impact executive functions, motor control, cognition and learning and memory. © Steven P. Guerin


Reference: Nickell, Chelsea G. et al. ‘Recovery of Hippocampal-Dependent Learning Despite Blunting Reactive Adult Neurogenesis After Alcohol Dependence’. 1 Jan. 2020 : 83 – 101. https://content.iospress.com/articles/brain-plasticity/bpl200108


Provided by IOS Press

Study Reveals Platinum’s Role in Clean Fuel Conversion (Chemistry)

Identifying specific platinum atoms activated in a water gas shift reaction catalyst could guide the design of less costly efficient catalysts

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory, Stony Brook University (SBU), and other collaborating institutions have uncovered dynamic, atomic-level details of how an important platinum-based catalyst works in the water gas shift reaction. This reaction transforms carbon monoxide (CO) and water (H2O) into carbon dioxide (CO2) and hydrogen gas (H2)—an important step in producing and purifying hydrogen for multiple applications, including use as a clean fuel in fuel-cell vehicles, and in the production of hydrocarbons.

But because platinum is rare and expensive, scientists have been seeking ways to create catalysts that use less of this precious metal. Understanding exactly what the platinum does is an essential step.

The new study, published in Nature Communications, identifies the atoms involved in the catalyst’s active site, resolving earlier conflicting reports about how the catalyst operates. The experiments provide definitive evidence that only certain platinum atoms play an important role in the chemical conversion.

“Part of the challenge is that the catalyst itself has a complex structure,” explained lead author Yuanyuan Li, a research scientist at SBU’s Materials Science and Chemical Engineering Department who has a guest appointment in Brookhaven Lab’s Chemistry Division and works under the guidance of Brookhaven/SBU joint appointee Anatoly Frenkel.

Scientists studying a water gas shift reaction catalyst made of platinum atoms (red and blue) on a cerium oxide (CeOx) surface discovered that only some platinum atoms around the periphery of the nanoparticle (shiny dark red) get activated to take part in the reaction. These activated platinum atoms transfer oxygen from OH groups (originally from water molecules) to carbon monoxide (CO), transforming it to CO2, leaving the H to combine with atomic hydrogen to form H2. Understanding these dynamics may help scientists design catalysts that require fewer platinum atoms.

“The catalyst is made of platinum nanoparticles (clumps of platinum atoms) sitting on a cerium oxide (ceria) surface. Some of those platinum atoms are on the surface of the nanoparticle, some are in the core; some are at the interface with ceria, and some of those are at the perimeter—the outside edges—of that interface,” Li said. “Those positions and how you put the particles on the surface may influence which atoms will interact with the support or with gas molecules, because some are exposed and some are not.”

Earlier experiments had produced conflicting results about whether the reactions occur on the nanoparticles or at single isolated platinum atoms, and whether the active sites are positively or negatively charged or neutral. Details of how the ceria support interacts with the platinum to activate it for catalytic activity were also unclear.

“We wanted to address these questions,” said Li. “To identify the active site and determine what is really happening at this site, it is better if we can investigate this type of catalyst at the atomic level,” she noted.

The team, which included scientists from Brookhaven’s Center for Functional Nanomaterials (CFN) and other institutions throughout the U.S. and in Sweden, used a range of techniques to do just that. They studied the catalyst under reaction conditions and, unexpectedly, captured a peculiar effect that occurred when the catalysts reached their active state in reaction conditions.

Study co-authors Anatoly Frenkel, Lihua Zhang, Sanjaya Senanayake, and Yuanyuan Li outside the Chemistry building at Brookhaven National Laboratory.

“The platinum atoms at the perimeter of the particles were ‘dancing’ in and out of focus in an electron microscopy experiment carried out by our collaborators, while the rest of the atoms were much more stable,” Frenkel said. Such dynamic behavior was not observed when some of the reactants (CO or water) were removed from the stream of reacting molecules.

“We found that only the platinum atoms at the perimeter of the interface between the nanoparticles and ceria support provide the catalytic activity,” Li said. “The dynamic properties at these perimeter sites allow the CO to get oxygen from the water so it can become CO2, and the water (H2O) loses oxygen to become hydrogen.”

Now that the scientists know which platinum atoms play an active role in the catalyst, they may be able to design catalysts that contain only those active platinum atoms.

“We might assume that all the surface platinum atoms are working, but they are not,” Li said. “We don’t need them all, just the active ones. This could help us make the catalyst less expensive by removing the atoms that are not involved in the reaction. We believe that this mechanism can be generalized to other catalytic systems and reactions,” she added.

Experimental details

Electron microscopy “snapshots” at the CFN and at the National Institute of Standards and Technology revealed the dynamic nature of the perimeter platinum atoms. “In some images, the perimeter site is there, you can see it, but in some images it is not there. This is evidence that these atoms are very dynamic, with high mobility,” Li said.

Infrared (IR) spectroscopy studies in Brookhaven’s Chemistry Division revealed that the appearance of the perimeter sites coincided with “oxygen vacancies”—a kind of defect in the cerium oxide surface. These studies also showed that CO tended to migrate across the platinum nanoparticle surface toward the perimeter atoms, and that hydroxy (OH) groups lingered on the ceria support near the perimeter platinum atoms.

“So it seems like the perimeter platinum atoms bring the two reactants, CO and OH (from the water molecules) together,” Li said.

X-ray photoelectron spectroscopy studies in Chemistry revealed that perimeter platinum atoms also became activated—changed from a nonmetallic to a metallic state that could capture oxygen atoms from the OH groups and deliver that oxygen to CO. “This really shows that these activated perimeter platinum sites enable the reaction to take place,” Li said.

A final set of experiments—x-ray absorption spectroscopy studies conducted at the Advanced Photon Source (APS) at DOE’s Argonne National Laboratory—showed the dynamic structural changes of the catalyst.

“We see the structure is changing under reaction conditions,” Li said.

Those studies also revealed an unusually long bond between the platinum atoms and the oxygen on the ceria support, suggesting that something invisible to the x-rays was occupying space between the two.

“We think there is some atomic hydrogen between the nanoparticle and the support. X-rays can’t see light atoms like hydrogen. Under reaction conditions, those atomic hydrogens will recombine to form H2,” she added.

The structural features and details of how the dynamic changes are connected to reactivity will help the scientists understand the working mechanism of this particular catalyst and potentially design ones with better activity at lower cost. The same techniques can also be applied to studies of other catalysts.

Brookhaven Lab’s role in this work was funded by the DOE Office of Science (BES). CFN and APS are DOE Office of Science user facilities. Additional collaborating institutions include the University of Illinois, Arizona State University, the University of Maryland, and the KTH Royal Institute of Technology in Stockholm.

Featured image: Lead author Yuanyuan Li, a research scientist at Stony Brook University’s Materials Science and Chemical Engineering Department who has a guest appointment in Brookhaven Lab’s Chemistry Division, performs an analysis on a sample using an infrared spectrometer.


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Provided by Brookeshaven National Laboratory

Astronomers Uncover Mysterious Origins Of ‘Super-Earths’ (Planetary Science)

Study shows super-Earths are not leftovers of mini-Neptunes, challenging our understanding of planetary formation

Mini-Neptunes and super-Earths up to four times the size of our own are the most common exoplanets orbiting stars beyond our solar system. Until now, super-Earths were thought to be the rocky cores of mini-Neptunes whose gassy atmospheres were blown away. In a new study published in The Astrophysical Journal, astronomers from McGill University show that some of these exoplanets never had gaseous atmospheres to begin with, shedding new light on their mysterious origins.

From observations, we know about 30 to 50 percent of host stars have one or the other, and the two populations appear in about equal proportion. But where did they come from?

One theory is that most exoplanets are born as mini-Neptunes but some are stripped of their gas shells by radiation from host stars, leaving behind only a dense, rocky core. This theory predicts that our Galaxy has very few Earth-sized and smaller exoplanets known as Earths and mini-Earths. However, recent observations show this may not be the case.

To find out more, the astronomers used a simulation to track the evolution of these mysterious exoplanets. The model used thermodynamic calculations based on how massive their rocky cores are, how far they are from their host stars, and how hot the surrounding gas is.

“Contrary to previous theories, our study shows that some exoplanets can never build gaseous atmospheres to begin with,” says co-author Eve Lee, Assistant Professor in the Department of Physics at McGill University and the McGill Space Institute.

The findings suggest that not all super-Earths are remnants of mini-Neptunes. Rather, the exoplanets were formed by a single distribution of rocks, born in a spinning disk of gas and dust around host stars. “Some of the rocks grew gas shells, while others emerged and remained rocky super-Earths,” she says.

How mini-Neptunes and super-Earths are born

Planets are thought to form in a spinning disk of gas and dust around stars. Rocks larger than the moon have enough gravitational pull to attract surrounding gas to form a shell around its core. Over time this shell of gas cools down and shrinks, creating space for more surrounding gas to be pulled in, and causing the exoplanet to grow. Once the entire shell cools down to the same temperature as the surrounding nebular gas, the shell can no longer shrink and growth stops.

For smaller cores, this shell is tiny, so they remain rocky exoplanets. The distinction between super-Earths and mini-Neptunes comes about from the ability of these rocks to grow and retain gas shells.

“Our findings help explain the origin of the two populations of exoplanets, and perhaps their prevalence” says Lee. “Using the theory proposed in the study, we could eventually decipher how common rocky exoplanets like Earths and mini-Earths may be.”

Featured image: Artists’s impression of one of more than 50 new exoplanets found by HARPS: the rocky super-Earth HD 85512 b | This artist’s impression shows the planet orbiting the Sun-like star HD 85512 in the southern constellation of Vela (The Sail). This planet is one of sixteen super-Earths discovered by the HARPS instrument on the 3.6-metre telescope at ESO’s La Silla Observatory. This planet is about 3.6 times as massive as the Earth lis at the edge of the habitable zone around the star, where liquid water, and perhaps even life, could potentially exist. Credit: ESO/M. Kornmesser


Reference: “Primordial Radius Gap and Potentially Broad Core Mass Distributions of Super-Earths and Sub-Neptunes” by Eve Lee and Nicholas Connors was published in The Astrophysical Journal. DOI: https://doi.org/10.3847/1538-4357/abd6c7


Provided by McGill University