Tuesday, October 03, 2023

Solar sails could reach Mars in just 26 days

by Laurence Tognetti, Universe Today

A recent study submitted to Acta Astronautica and currently available on the arXiv preprint server explores the potential for using aerographite solar sails for traveling to Mars and interstellar space, which could dramatically reduce both the time and fuel required for such missions.

This study comes while ongoing research into the use of solar sails is being conducted by a plethora of organizations along with the successful LightSail2 mission by The Planetary Society, and holds the potential to develop faster and more efficient propulsion systems for long-term space missions.

"Solar sail propulsion has the potential for rapid delivery of small payloads (sub-kilogram) throughout the solar system," Dr. René Heller, who is an astrophysicist at the Max Planck Institute for solar system Research and a co-author on the study, tells Universe Today. "Compared to conventional chemical propulsion, which can bring hundreds of tons of payload to low-Earth orbit and deliver a large fraction of that to the moon, Mars, and beyond, this sounds ridiculously small. But the key value of solar sail technology is speed."

Unlike conventional rockets, which rely on fuel in the form of a combustion of chemicals to exert an external force out the back of the spacecraft, solar sails don't require fuel. Instead, they use sunlight for their propulsion mechanism, as the giant sails catch solar photons much like wind sails catching the wind when traveling across water. The longer the solar sails are deployed, the more solar photons are captured, which gradually increases the speed of the spacecraft.

For the study, the researchers conducted simulations on how fast a solar sail made of aerographite with a mass up to 1 kilogram (2.2 pounds), including 720 grams of aerographite with a cross-sectional area of 104 square meters, could reach Mars and the interstellar medium, also called the heliopause, using two trajectories from Earth known as direct outward transfer and inward transfer methods, respectively.

The direct outward transfer method for both the trip to Mars and the heliopause involved the solar sail both deploying and departing directly from a polar orbit around the Earth. The researchers determined that Mars being in opposition (directly opposite Earth from the sun) at the time of solar sail deployment and departure from Earth would yield the best results for both velocity and travel time.

This same polar orbit deployment and departure was also used for the heliopause trajectory, as well. For the inward transfer method, the solar sail would be delivered to approximately 0.6 astronomical units (AU) from the sun via traditional chemical rockets, where the solar sail would deploy and begin its journey to either Mars or the heliopause. But how does an aerographite solar sail make this journey more feasible?

"With its low density of 0.18 kilograms per cubic meter, aerographite undercuts all conventional solar sail materials," Julius Karlapp, who is a Research Assistant at the Dresden University of Technology and lead author of the study, tells Universe Today. "Compared to Mylar (a metallized polyester foil), for example, the density is four orders of magnitude smaller. Assuming that the thrust developed by a solar sail is directly dependent on the mass of the sail, the resulting thrust force is much higher. In addition to the acceleration advantage, the mechanical properties of aerographite are amazing."

Through these simulations, the researchers found the direct outward transfer method and inward transfer method resulted in the solar sail reaching Mars in 26 days and 126 days, respectively, with the first 103 days being the travel time from Earth to the deployment point at 0.6 AU.

For the journey to the heliopause, both methods resulted in 5.3 years and 4.2 years, respectively, with the first 103 days of the inward transfer method also being devoted to the travel time from the Earth to the deployment point at 0.6 AU, as well. The reason the heliopause is reached in a faster time with the inward transfer method is due to the solar sail achieving maximum speed at 300 days, as opposed to achieving maximum speed with the outward transfer method at approximately two years.

Current travel times to Mars range between 7 and 9 months, which only happens during specified launch windows every two years while relying on the positions of both planets to be aligned at both launch and arrival of any spacecraft going to, or coming from, Mars. Estimating current travel times to the heliopause can be done using NASA's Voyager 1 and Voyager 2 probes, which reached the heliopause at approximately 35 years and 41 years, respectively.

The researchers note that one major question of using solar sails is deceleration, or slowing down, upon arriving at the destination, specifically Mars, and while they mention aerocapture as one solution, they admit this still requires further study.

"Aerocapture maneuvers for hyperbolic trajectories (like flying from Earth to Mars) use the atmosphere to gradually reduce velocity due to drag," Dr. Martin Tajmar, who is a physicist and Professor of Space System at the Dresden University of Technology and a co-author on the study, tells Universe Today.

"Therefore, less fuel is required to enter the Martian orbit. We use this braking maneuver to eliminate the need for additional braking thrusters, which in turn reduces the mass of the spacecraft. We're currently researching what alternative strategies might work for us. Yet the braking method is only one of many different challenges we are currently facing."

While solar sail technology has been proposed by NASA as far back as the 1970s, a recent example of solar sail technology is the NASA Solar Cruiser, which is currently scheduled to launch in February 2025.

More information: Julius Karlapp et al, Ultrafast transfer of low-mass payloads to Mars and beyond using aerographite solar sails, arXiv (2023). DOI: 10.48550/arxiv.2308.16698

Provided by Universe Today LightSail 2 has been flying for 30 months now, paving the way for future solar sail missions

Samuel Delany-Nova PDF

Scribd

https://www.scribd.com › doc › Sa...

Semjuel Dilejni. K e n ta u r. N a u n a fa n ta s tik a. Biblioteka. Kentaur. Nauna fantastika. N aslov originala. Sam uel Delany. NOVA

Cultural adaptation study shows what's better for the individual isn't always better for the group

by Liana F. Wait, University of Pennsylvania

crowd — Credit: Unsplash/CC0 Public Domain

Humans are arguably the most adaptable species on Earth. The species' enormous capacity to adapt and live in different environments is thanks to cumulative culture, the transmission and continuous improvement of knowledge and technologies between individuals and generations.

Now, researchers from the School of Arts & Sciences have uncovered a source of inherent tension between individuals and the groups they live in. In a study published in Evolutionary Human Sciences, they show that individuals may be better off with fewer social connections, but groups do best when they consist of very dense social networks.

"Our capacity to accumulate cultural knowledge is part of what makes us human, and it's what has enabled us to settle and live all over the globe," says theoretical biologist Erol Akçay, an associate professor of biology. "In the real world, groups and individuals can benefit from either accumulating more traits or higher proficiency or both."

Akçay and evolutionary biologist Marco Smolla used a model to investigate the coevolution of social networks and cumulative culture. Specifically, they explored the relative benefits of specialist versus generalist cultures for individuals and groups.

Importantly, their model relied on the assumption that in order to learn socially an individual must be exposed to new skills or information multiple times.

"We were interested in complicated traits that a person would need to be exposed to multiple times in order to learn, for example, foraging tactics or making tools," says Smolla, who is a former postdoctoral fellow in Penn's Department of Biology and now a researcher at the Max Planck Institute for Evolutionary Anthropology.

The researchers found that groups benefit most when they have a specialist culture where everyone is highly connected. "Social learning is more effective, and more culture accumulates in these specialist cultures where everyone becomes very proficient at the same handful of traits because there are no wasted learning opportunities," Akçay says. "But there's a conflict between individual-level incentives and what's best for the group."

The model showed that once groups are densely connected, there is an individual incentive to make fewer connections because it allows individuals to focus more and learn more effectively. The researchers also found that while individuals benefit from being innovative, too much innovation is disadvantageous for the group. This mismatch between individual and group interests eventually leads to the disintegration of specialist cultures which results in populations cycling between generalist and specialist cultures.

"Cumulative culture becomes a public good because to maintain it groups have to have this connected network structure, but maintaining that network is individually costly," Akçay says. "I do wonder if these cycling dynamics connect in some way to the archaeological phenomenon where you have a very vibrant culture that builds up and then suddenly collapses."

The researchers also explored how environmental stability might impact social learning and culture. They found that environmental stability promotes more specialized cultures, whereas highly variable environments favor generalist cultures. "Rapid environmental turnover favors disconnected groups because individuals are selected to increase their repertoire size in order to maximize the probability of learning at least some high-payoff traits," Smolla says.

The conflict between individuals and groups could also explain the cross-cultural ubiquity of social rituals that function to maintain social networks and the presence of social norms that enforce social learning at the expense of individual innovation.

"Our results provide a novel hypothesis for the evolution of rituals and social norms that promote social connections," Smolla says. "Such rituals can enforce connectivity and cultural convergence, which might give the group an advantage over competing groups."

More information: Marco Smolla et al, Pathways to cultural adaptation: the coevolution of cumulative culture and social networks, Evolutionary Human Sciences (2023). DOI: 10.1017/ehs.2023.21

Provided by University of Pennsylvania A society's cultural practices shape the structure of its social networks

Environmental physicist discusses marine heat waves

by Dr. Nicolas Gruber, ETH Zurich

The seas are in extremis — Global average sea surface temperature (1982–2011). The mean is dashed in black; the

An extraordinary heat wave is assailing the world's oceans with an intensity that is surprising climate researchers. Environmental physicist Nicolas Gruber provides some context.

Record temperatures in the Mediterranean. Huge heat wave in the North Atlantic. The temperature of the oceans at an all-time high. The ocean's fever chart has been covered in the media since early summer. While this was probably the first time many people in Switzerland had heard of marine heat waves, these reports came as little surprise to me.

As climate scientists, we understand very well how human-induced global warming is also pushing up ocean temperatures. The ocean is the primary thermal buffer in the Earth's climate system, absorbing more than 90%t of the additional heat resulting from greenhouse gases such as CO2.

So, in and of itself, it's not surprising that marine heat waves are becoming more frequent and intense. But I have to admit that I wasn't prepared for what's currently happening in the oceans: the intensity and magnitude of the heat waves is enormous, and the rapidity of the warming fills me with concern.

In uncharted territory

In recent weeks, the global average temperature of the sea surface has reached 21.1° Celsius—the highest ever recorded. That's 0.3° warmer than the previous record temperature at this time of year. Since the spring, the temperature curve for 2023 has been about 1° above the 1982–2011 average.

Without a doubt, the current sea surface temperatures are way out of the ordinary. The ocean is moving in uncharted territory—and climate science is struggling to anticipate these movements.

We don't yet fully understand the factors that have caused ocean temperatures to jump to these new highs. Certainly, the emerging El Niño event is an important driver. We know from past experience that an El Niño increases the global average sea surface temperature by about 0.1 to 0.2° Celsius. However, this effect tends to come later in the year, when El Niño reaches its peak around the turn of the year.

Furthermore, we're currently observing two huge heat waves in the North Pacific and the North Atlantic, which got underway at the beginning of the year and have intensified and expanded in recent months. This combination of El Niño and extratropical heat waves is driving up global ocean temperatures tremendously, especially since hardly any ocean region is significantly cooler than normal at present.

A perfect storm

The question is, did this combination of factors occur by coincidence—or is there something driving it? In my assessment, much of it is in fact coincidence. El Niño may well have amplified the North Pacific heat wave, similar to what happened during the monster North Pacific heat wave known as "the Blob" from 2013 to 2015. But there's no evidence linking El Niño to the North Atlantic heat wave.

I therefore argue that we're dealing with a perfect storm—an extraordinary situation where various factors happen to come together in such a way that they reinforce each other. However, it's also important to note that without human-induced global warming, this perfect storm could never have generated such high temperatures.

Stable high-pressure conditions promote heat waves

So, while a marine heat wave's timing is largely random, there are conditions that favor its formation. These include stable high-pressure systems—extensive regions of good weather that can persist for long periods of time and thus promote heat waves, both on land and at sea.

Atmospheric and oceanic circulation outside the tropics play an important role here. "Circulation" refers to large-scale currents, such as the jet stream in the atmosphere or the meridional overturning circulation in the North Atlantic.

In an ideal world, we could model future circulation patterns to identify favorable conditions for heat waves early on. Unfortunately, the circulation patterns underlying stable high-pressure systems can't be predicted much beyond a few days or a few weeks at most.

This is mainly due to small-scale turbulence, which is the reason two possible weather developments with only small differences in initial or boundary conditions can rapidly drift far apart; the phenomenon is often referred to as the butterfly effect.

So, if we can't determine individual occurrences, we should at least be able to predict whether a warmer climate will cause such stable circulation patterns to occur more often and for longer periods—in other words, whether conditions that could promote heat waves will become more frequent. But therein lies the rub.

Blurred circulation

There is little consensus among climate scientists on this question, just as we can't predict whether El Niño will become more frequent or more infrequent in the future. We also don't really agree on whether or not the meridional overturning circulation in the North Atlantic will weaken much. Or whether the jet stream in the atmosphere will be altered. These are all relevant questions that have a strong impact on exactly how climate change will affect different regions of the world.

A common challenge underlying all these questions is that both atmospheric and oceanic circulation are not only determined by large-scale processes, but also substantially modified by small-scale processes. These are weather processes such as convection, cloud formation, thunderstorms or storms—processes that take place on scales of one to a few kilometers. In other words, circulation is a phenomenon determined by interactions among all spatial scales.

But it is precisely these scale interactions that the climate models we typically use today don't simulate. This is primarily because the resolution of the models is too low.

With today's grid spacing of around a hundred kilometers, the models aren't fine enough to correctly represent many elementary processes of weather in the atmosphere or the ocean. And yet it's exactly these kinds of small-scale weather processes that strongly influence large-scale weather situations (and vice versa). At present, we generally have to estimate them or model them using highly simplified methods, which leads to sizable uncertainties.

That means the challenge is still on for climate and weather researchers to develop their models further, especially with respect to the resolution and accuracy, with which we can map changes in circulation and thus changes in weather patterns. We at ETH Zurich are working on this together with MeteoSwiss in the EXCLAIM project and on an international level with EVE.

We expect this to lead to a more detailed understanding of circulation and ultimately to more consensus on the big questions in climate research. And most importantly, we need to increase the accuracy of local and regional assessments of climate change so we can work out how best to adapt.

Provided by ETH Zurich North Atlantic Oscillation contributes to 'cold blob' in Atlantic Ocean

Study explores supergiant iceberg's huge impact on surrounding ocean surface

by British Antarctic Survey

Supergiant iceberg makes surrounding ocean surface colder and less salty — The melting of the supergiant iceberg A-68 had a huge impact on the ocean around South

The melting of the supergiant iceberg A-68 had a huge impact on the ocean around South Georgia, in sub-Antarctica, and significantly changed the Southern Ocean's temperature and saltiness, with potentially major consequences for this ecologically significant region. These results are published this week in the journal Geophysical Research Letters.

In 2020, A-68—a supergiant iceberg about the size of Luxembourg that calved from the Larsen C ice shelf in 2017—drifted very close to South Georgia before starting to break up, releasing huge quantities of fresh, cold meltwater in a relatively small region.

Researchers from British Antarctic Survey and University of Sheffield used satellite data to observe how the melting iceberg affected the temperature and saltiness, or salinity, of the top few centimeters of the ocean surface.

They observed the meltwater caused extreme anomalies in the temperature and saltiness of the waters at the ocean surface, of magnitudes that have not been reported for any previous iceberg disintegration so far. Researchers recorded temperatures up to 4.5°C colder than average. The salinity was reduced by more than 10 psu (a way of measuring the amount of salt in water) meaning the surface ocean became around two-thirds of its normal saltiness.

This "signal" from the melted iceberg eventually extended well beyond South Georgia; it was carried by ocean currents to form a long plume that stretched up to more than 1,000km across the South Atlantic—roughly the distance from Land's End to John O'Groats.

The meltwater signal also took a long time to disappear—it was still visible more than two months after the iceberg disintegrated.

These changes to the physical conditions at the ocean surface have important links to the biological conditions. For example, meltwater contains dissolved iron which stimulates the growth of microscopic plants called phytoplankton that form the base of the ocean's food web.

However, this meltwater can also have negative impacts, altering the temperature, salinity and nutrient conditions that many of the Southern Ocean's inhabitants are adapted to thrive in.

The calving of this massive iceberg created a unique opportunity to assess the impact melting on surface ocean conditions.

Climate scientist Roseanne Smith at British Antarctic Survey and co-author of the study said, "The A-68 iceberg was one of the largest and most studied of all icebergs. When it started to break apart, it was a bit like installing a major river estuary into the open ocean, pumping cold, freshwater into the surface layer.

"Our results show that each individual melting giant iceberg can have widespread and long-lasting impacts on the conditions at the surface of the Southern Ocean, and this has consequences for the plant and animal life that lives there."

Emeritus Professor Grant Bigg, from the University of Sheffield, said, "This is the largest iceberg whose impact on the Southern Ocean has been tracked for all of its lifetime, with this impact being widespread and long-lasting. We know it collided with the continental shelf off South Georgia, so it will have left long term scars on the seafloor there, as well as the major ocean cooling and freshening likely changing local ocean surface flows.

"Climate change is likely to see more giant iceberg calving in the future; it is important to monitor these so future impacts on ocean circulation, biology and seafloor geology can be assessed and predicted."

Almost half the mass lost from the Antarctic Ice Sheet is from calved icebergs—they release huge quantities of cold, fresh water as they drift and break up, affecting the temperature and salinity of the Southern Ocean. These changes have wide ranging impacts, such as affecting sea ice growth and local currents, and also releases nutrients and iron into the water, stimulating primary production.

Supergiant icebergs, like A-68, may become more common in the future as the climate warms, causing Antarctic ice shelves to break up.

More information: R. M. Smith et al, Impact of Giant Iceberg A68A on the Physical Conditions of the Surface South Atlantic, Derived Using Remote Sensing, Geophysical Research Letters (2023). DOI: 10.1029/2023GL104028

Journal information: Geophysical Research Lette

Provided by British Antarctic Survey

Modeling suggests iceberg A68's second break was due to ocean current shear forces

Opinion: As space exploration and colonization expand, off-Earth resources will create a booming market

by Serkan Saydam, Andrew Dempster, University of New South Wales

moonrise — Credit: Pixabay/CC0 Public Domain

The drive to explore deeper into space and establish colonies on other planets has intensified over the last decade, and with it the importance of space resources extraction.

Obtaining valuable resources and minerals, even in extreme environments, has long been attractive to humans. We have a history of facing hazards in search of valuable resources. From the gold rush in the 1800s to the recent surge in space resources, humans have been willing to take risks to find and collect scarce and profitable materials.

With advances in space technology, we're on the edge of the next gold rush—but not on Earth. Based on recent scientific and engineering breakthroughs and commercial interests, off-Earth mining is expected to begin in the next decade.

Potential mining sites include the moon, Mars and its moons, asteroids and even comets. Market predictions for lunar mining, particularly lunar water, project a multibillion-dollar industry by 2050. Although theoretical, these forecasts signal a worthwhile market, with Australia as a potential leader.

The motivation for off-Earth mining is multifaceted: access to an unlimited wealth of valuable space resources, the spirit of discovering new planets and the development of spin-off technologies to be used back on Earth.

NASA's Artemis program, which Australia supports via its signing of the Artemis Accords, is aiming for a lunar colony and eventually one on Mars. The only way to reduce the enormous costs of transporting resources from Earth will be through the establishment of self-sustaining infrastructure.

Water is an essential starting point. When converted to oxygen and hydrogen, it can be used as a propellant for rockets for further space missions. Given the vast reserves of lunar ice, it's a sustainable and economical source compared with Earthly transport.

The Australian Center for Space Engineering Research, based at the University of New South Wales, is at the forefront of this endeavor, merging terrestrial mining engineering expertise with space research. The Off-Earth Mining Forum was founded in Sydney in 2013. Since then, it has run every two years. In August the year, the first non-Sydney-based event took place in Perth, Western Australia.

Its primary objective is to position Australia as a global leader in in-situ resource utilization by harnessing space resources to reduce potential risks of off-Earth mining. This encompasses using lunar regolith (soil) for construction or mineral extraction, focusing on lunar water.

However, off-Earth mining has many challenges: there are geological uncertainties—we don't know exactly where the water is and how much there is; infrastructural needs such as landing pads; social considerations—people have a strong emotional attachment to the moon; and financial constraints, with high risk but high potential return.

Mining is a challenging industry that constantly confronts extreme conditions and volatile markets. Despite these obstacles, mining has continued to attract businesses due to the potential for high financial returns. In many cases, mining operations have been a driving force behind the settlement of new territories.

Looking toward the future, the mining industry is working towards zero-entry mines (with no human access required) and invisible mines (low-impact, reduced-footprint mining sites) to reduce the effect on the environment, improve energy efficiency and achieve decarbonization.

Improved social acceptance and reputation are also critical for the mining industry's future. The space resources industry is motivated by colonization and creating a market for its product.

The mining and space sectors both thrive in challenging environments, making collaboration essential. They can mutually benefit, with the mining sector gaining from systems engineering and autonomous technology, while space can leverage operational experience and market creation.

The path ahead is loaded with uncertainties, but merging mining knowledge with space exploration will be paramount in the years ahead.

Provided by University of New South Wales

Originally published under Creative Commons by 360info

Humans have big plans for mining in space, but there are many things holding us back

Researchers identify tiny, unique sea creature photographed in 2018

An international team of zoologists and parasitic worm specialists has identified an odd sea creature captured by an underwater photographer in 2018 off the coast of Okinawa. In their project, reported in the open-access journal Current Biology, the group obtained and studied a sample of the sea creature.

Shortly after he captured images of the creature, photographer Ryo Minemizu posted them online, asking if anyone knew what it was. None of his followers had seen anything like it before. Intrigued, Minemizu went back to where he had seen the creature and found it, or another one like it. He captured the ladybug-sized creature and stored it until it caught the attention of the research team. Minemizu sent them the sample and then awaited the results of their investigation.

The research team found that it was actually two creatures holding tightly to one another. Both were types of cercariae—parasitic larvae worms. The researchers dubbed one type "sailors" and the other "passengers," because of the roles they played when bonded together.

The passengers were much smaller than the sailors, and the two held tightly to one another, forming a flat-topped hemisphere. They squeezed themselves together with their heads pointed toward the inside of the sphere, leaving their tails exposed and forming the exterior of the hemisphere. The sailors latched onto the passenger tails with their own tails and stretched out their bodies into the water, resembling appendages of the sphere.

Swimming colony of sailor and passenger cercariae after being sampled in Okinawa. Credit: Current Biology (2023). DOI: 10.1016/j.cub.2023.08.090

Further study of the two-creature grouping showed that the sailors used their bodies like appendages, swinging them like cilia on paramecia. And like the cilia, the sailors moved their bodies in unison as a means of moving the combined mass around in the water.

The researchers found that such swimming was typically initiated by just one member of the group—its actions were mimicked by those nearby until all were waving, pushing the aggregate through the water. By doing so, the collectivized group could make sudden movements, jumping from point to point, or it could move steadily. The researchers suggest the two creatures have formed a colonial organism that suits the needs of both groups.

More information: Darya Krupenko et al, Polymorphic parasitic larvae cooperate to build swimming colonies luring hosts, Current Biology (2023). DOI: 10.1016/j.cub.2023.08.090

Journal information: Current Biology

Engineers create artificial cilia at the microscale

Wildlife mitigating measures no help for Ottawa's freshwater turtles, says study

by University of Ottawa

Urban sprawl and insufficient relief measures have left an Ottawa-area freshwater turtle facing extinction within the decade, says new research from the University of Ottawa and Trent University, which tracked changes to the turtle's habitat over a 10-year period.

Specifically, the development of Terry Fox Drive in the city's west end has led to a dangerous decline in the Blanding's turtle's (Emydoidea blandingii) habitat, leading to a 70% decline in adult population size, despite mitigating measures such as wildlife fencing, new wetlands and wildlife passage placement.

The study, "Demographic evidence that development is not compatible with sustainability in semi-urban freshwater turtles," was published in Animal Conservation.

From Threatened status to nearing extinction

Professor Gabriel Blouin-Demers, alongside lead author Anne-Christine Auge, Ph.D. candidate, and Dennis Murray from Trent University, tracked changes in freshwater turtle habitat over a decade while conducting a population viability analysis to predict future population trends. The analysis revealed that the turtle will reach its quasi-extinction threshold within the next few years.

"There was a lot of opposition to the development along Terry Fox Drive, precisely because of the presence of Blanding's turtles," says Blouin-Demers, a full professor in the Department of Biology of the Faculty of Science. "Now we know that the project will have caused the extinction of the population."

The Blanding's turtle's preferred habitat

Easy to recognize with their yellow throats, Blanding's turtles enjoy beaver ponds, wetlands and shallow lakes, where they hibernate in the mud in the winter and sunbathe in the summer. But their habitats are being destroyed by urbanization, which includes loss of access to water and food sources, rising noise levels, pollution, artificial lighting and increased risk of road mortalities.

"We mustn't delude ourselves into thinking that when it comes to turtle conservation, we can have our cake and eat it too," says Blouin-Demers. "Current mitigating measures are not enough."

The authors show that current urban development is incompatible with the Blanding's turtle's survival and call for robust oversight and conservation efforts to safeguard at-risk species in urbanizing areas.

More information: A.‐C. Auge et al, Demographic evidence that development is not compatible with sustainability in semi‐urban freshwater turtles, Animal Conservation (2023). DOI: 10.1111/acv.12903

Provided by University of Ottawa

Salmonella outbreak brings CDC warning over small turtles

POSTMODERN ALCHEMY

Gold nanoclusters can improve electrochemical water splitting to produce hydrogen

by Tsinghua University Press

As energy demand continues to rise, research into new, efficient renewable and clean energy sources is an urgent priority. Currently, renewable energy sources like solar, wind, tide, and geothermal make up less than 40% of the current energy demand. Increasing this percentage and reducing the amount of fossil fuels used will require other, more efficient renewable and clean energy sources.

Hydrogen is a promising alternative, but it is currently produced using steam reforming, which is inefficient and produces CO2 emissions. Electrochemical water splitting, also called water electrolysis, can take advantages of the electricity generated from renewable sources, is a potential efficient solution to produce hydrogen.

Water splitting requires a reaction called hydrogen evolution reaction (HER), but the nanocatalysts involved in this HER do not have uniform size, composition, structure, or chemical coordination environment to improve the efficiency and promote the reaction mechanistic understanding. The solution to this problem may lie in atomically precise gold nanoclusters.

In a literature review published in Polyoxometalates on August 19, the researchers summarize existing work that studies how gold nanoclusters can improve catalytic performance and promote HER.

"It is extremely difficult to achieve a model catalyst with absolute uniform size, definite geometric configuration, and a well-defined local chemical environment at the anatomical level to establish the unambiguous atomical-level structure-performance relationship. Atomically precise gold nanoclusters can potentially resolve those issues," said Zhenghua Tang, a researcher at the New Energy Research Institute at the South China University of Technology in Guangzhou, China. "Specifically, gold nanoclusters have demonstrated extraordinary catalytic properties in various organic reactions and electrocatalytic reactions."

Gold nanocluster is uniquely suited to be a catalyst for HER for several reasons. Unlike other nanocatalysts, gold nanocluster has a precise nanostructure. This precise structure means that all gold nanoclusters are uniform in size, composition, morphology, and chemical environment.

It is also helpful for identifying the active sites for HER catalysis. The rich chemical reactivities of gold nanoclusters allow for both metal core tailoring and surface ligand engineering. Metal core tailoring is when another metal is introduced to the gold nanocluster, which forms a gold-alloy cluster. Introducing another metal can endow novel catalytic capabilities and cut down the cost. In surface ligand engineering, the surface chemical environment can be fine-tuned to expose more active sites or change the structure of the nanocluster.

Finally, gold nanoclusters have other structural merits, such as the size is ultrasmall, which meets the principle of "small is precious" in catalysis field; the morphology can be tuned and manipulated; robust stability with intact structure preserved in various reaction under mild conditions.

"The cases presented in this review clearly show that exceptional HER catalytic properties are often displayed because of the distinct advantages of gold nanoclusters compared to gold nanoparticles. However, challenges are certainly present in employing gold nanoclusters for HER catalysis," said Tang.

Some of the common challenges associated with gold nanoclusters are finding a solution to the amount of gold that would be required to scale the use of these catalysts, problems with how the nanocatalysts perform in harsh conditions, and inaccurate theoretical modeling.

Looking ahead, researchers are planning what the next steps in nanocatalyst research should be. Suggested avenues include testing the applicability of the gold cluster-based composite for other reactions coupled with HER and improving the electrical conductivity of the cluster-based composite catalyst.

"Due to the rapid development of synthetic techniques and catalysis science, we anticipate more research efforts will be dedicated to using atomically precise metal nanoclusters as model catalysts for various electrocatalytic reactions and beyond," said Tang.

More information: Xin Zhu et al, Atomically precise Au nanoclusters for electrochemical hydrogen evolution catalysis: Progress and perspectives, Polyoxometalates (2023). DOI: 10.26599/POM.2023.9140031

Provided by Tsinghua University Press

Atomically precise noble metal nanoclusters

LA REVUE GAUCHE - Left Comment