One major challenge stretchable electronics must overcome is the stiff and inflexible nature of their energy storage components, batteries and supercapacitors. Supercapacitors that use electrodes made from transitional metal carbides, carbonitrides or nitrides, called MXenes, have desirable electrical properties for portable flexible devices, such as rapid charging and discharging. And the way that 2D MXenes can form multi-layered nanosheets provides a large surface area for energy storage when they’re used in electrodes. However, previous researchers have had to incorporate polymers and other nanomaterials to keep these types of electrodes from breaking when bent, which decreases their electrical storage capacity. So, Desheng Kong and colleagues wanted to see if deforming a pristine titanium carbide MXene film into accordion-like ridges would maintain the electrode’s electrical properties while adding flexibility and stretchability to a supercapacitor.

The researchers disintegrated titanium aluminum carbide powder into flakes with hydrofluoric acid and captured the layers of pure titanium carbide nanosheets as a roughly textured film on a filter. Then they placed the film on a piece of pre-stretched acrylic elastomer that was 800% its relaxed size. When the researchers released the polymer, it shrank to its original state, and the adhered nanosheets crumpled into accordion-like wrinkles.

In initial experiments, the team found the best electrode was made from a 3 µm-thick film that could be repetitively stretched and relaxed without being damaged and without modifying its ability to store an electrical charge. The team used this material to fabricate a supercapacitor by sandwiching a polyvinyl(alcohol)-sulfuric acid gel electrolyte between a pair of the stretchable titanium carbide electrodes. The device had a high energy capacity comparable to MXene-based supercapacitors developed by other researchers, but it also had extreme stretchability up to 800% without the nanosheets cracking. It maintained approximately 90% of its energy storage capacity after being stretched 1,000 times, or after being bent or twisted. The researchers say their supercapacitor’s excellent energy storage and electrical stability is attractive for stretchable energy storage devices and wearable electronic systems.

The authors acknowledge funding from the Key Research and Development Program of Jiangsu Provincial Department of Science and Technology of China, China Postdoctoral Science Foundation and High-Level Entrepreneurial and Innovative Talents Program of Jiangsu Province.

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Shape memory polymers alternate between an original, undeformed state and a secondary, deformed state. The deformed state is created by stretching the polymer and is held in place by molecular changes, such as dynamic bonding networks or strain-induced crystallization, that are reversed with heat or light. The polymer then returns to its original state through the release of stored entropic energy. But it’s been challenging for scientists to make these polymers perform energy-intensive tasks. Zhenan Bao and colleagues wanted to develop a new type of shape memory polymer that stretches into a stable, highly elongated state, allowing it to release large amounts of energy when returning to its original state.

The researchers incorporated 4-,4′-methylene bisphenylurea units into a poly(propylene glycol) polymer backbone. In the polymer’s original state, polymer chains were tangled and disordered. Stretching caused the chains to align and form hydrogen bonds between urea groups, creating supermolecular structures that stabilized the highly elongated state. Heating caused the bonds to break and the polymer to contract to its initial, disordered state.

In tests, the polymer could be stretched up to five times its original length and store up to 17.9 J/g energy — almost six times more energy than previous shape memory polymers. The team demonstrated that the stretched material could use this energy to lift objects 5,000 times its own weight upon heating. They also made an artificial muscle by attaching the pre-stretched polymer to the upper and lower arm of a wooden mannequin. When heated, the material contracted, causing the mannequin to bend its arm at the elbow. In addition to its record-high energy density, the shape memory polymer is also inexpensive (raw materials cost about $11 per lb) and easy to make, the researchers say.

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After a series of marine heatwaves hit the Phoenix Islands Protected Area (PIPA) in the central Pacific Ocean, a new study finds the impact of heat stress on the coral communities lessened over time.

While a 2002-2003 heatwave devastated coral communities in PIPA, the reefs recovered and experienced minimal losses during a similar event in 2009-2010. Then, in 2015-2016, a massive heatwave put twice as much heat stress on the corals, yet the die-off was much less severe than expected, according to new research published in Geophysical Research Letters, AGU’s journal for high-impact reports with immediate implications spanning all Earth and space sciences.

The authors of the new study suspect heat-tolerant offspring from the surviving corals are repopulating the reefs, allowing the community to keep pace with warming seas, at least for the time being.

The new study could help coral reef managers identify coral communities most likely to survive in the warming ocean, improving conservation and restoration outcomes.

“It’s easy to lose faith in coral reefs,” said first author Michael Fox, a postdoctoral scientist and coral reef ecologist at the Woods Hole Oceanographic Institution (WHOI). “But in PIPA, which is protected from local stressors, and where reefs have enough time to recover between heatwaves, the coral populations are doing better than expected.”

UNDERWATER HEATWAVES

Just like on land, heatwaves underwater are becoming more frequent and intense as the world warms, putting stress on ocean ecosystems. High temperatures hit coral reefs especially hard by causing widespread bleaching events, where corals eject the symbiotic algae in their tissues, further weakening the animals. With continued ocean warming, coral reefs face a dim future.

In the new study, researchers monitored coral communities at four islands within PIPA, an area encompassing over 400,000-square-kilometers of coral reef and deep-sea habitat. The Republic of Kiribati established the reserve in 2008, and the United Nations Educational, Scientific and Cultural Organization (UNESCO) designated PIPA as a World Heritage Site in 2010. “The protected area gives us a rare opportunity to study pristine and isolated coral reef ecosystems, a privilege for which we thank the people of Kiribati,” said co-author Anne Cohen, a marine scientist at WHOI.

The team used daily satellite data and temperature loggers to examine how each heatwave impacted the corals. They ruled out 11 environmental factors that might explain the higher-than-expected survival following the 2009-2010 and 2015-2016 heatwaves, such as greater cloud cover or more gradual warming.

After the 2002-2003 heatwave, the surveyed sites lost more than three-quarters of their coral cover. The reef was beginning to recover when the 2009-2010 heatwave hit, sparking fears of widespread bleaching, but two years later, coral cover had increased by more than 5%. Following the “Super El Niño” in 2015-2016, which raised ocean temperatures by 3 degrees Celsius (5.4 degrees Fahrenheit), the loss of coral cover was 40% — about half of the 2002 losses, despite causing twice the level of thermal stress.

A SOURCE OF HOPE FOR CORAL REEFS

Many of the reef-building species survived the heatwaves. “We’re seeing areas that were devoid of corals after 2002-2003 that are now flourishing with most of the original species,” Fox said.

At other reefs worldwide, sometimes only a handful of especially hardy or fast-growing species recover after a bleaching event. Coral larvae can float long distances on ocean currents, but due to PIPA’s isolation, the researchers hypothesize that local heat-tolerant individuals are repopulating the reefs.

Now that the researchers have shown that some coral communities have the potential to keep up with ocean warming, their next step is to figure out how they are doing it.

The findings are “important for giving us hope for the future of coral reefs, and also for helping to maintain support for protecting reefs, including efforts to reduce local threats, like pollution, sedimentation and overfishing that undermine the reefs’ ability to adapt,” said Lizzie McLeod, the Global Reef Systems Lead at the Nature Conservancy, who was not involved in the study.

She recommends reef conservationists prioritize the conservation of heat-tolerant reefs, because they can act as climate refuges that repopulate other sites decimated by heatwaves.

The study’s authors caution that even these remarkable corals have their limits and reversing climate change remains paramount. As heatwaves become more frequent or intense, even heat-tolerant communities could die out.

“We’re in a race against time, so anything that increases the chances that corals are going to make it is really good news,” said Nancy Knowlton, the Sant Chair in Marine Science Emerita at the Smithsonian National Museum of Natural History, who was not part of the study. “The corals are doing their part,” she said. “We have to do ours.”

Developed by researchers at RMIT University in Melbourne, Australia, the highly versatile catalysts are cost-effective to make and simple to scale.

The team’s lab demonstrations show the 3D printed catalysts could potentially be used to power hypersonic flight while simultaneously cooling the system.

The research is published in the Royal Society of Chemistry journal, Chemical Communications.

Lead researcher Dr Selvakannan Periasamy said their work tackled one of the biggest challenges in the development of hypersonic aircraft: controlling the incredible heat that builds up when planes fly at more than five times the speed of sound.

“Our lab tests show the 3D printed catalysts we’ve developed have great promise for fuelling the future of hypersonic flight,” Periasamy said.

“Powerful and efficient, they offer an exciting potential solution for thermal management in aviation — and beyond.

“With further development, we hope this new generation of ultra-efficient 3D printed catalysts could be used to transform any industrial process where overheating is an ever-present challenge.”

Need for speed

Only a few experimental planes have reached hypersonic speed (defined as above Mach 5 — over 6,100km an hour or 1.7km per second).

In theory, a hypersonic aircraft could travel fromLondon to New York in less than 90 minutes but many challenges remain in the development of hypersonic air travel, such as the extreme heat levels.

First author and PhD researcher Roxanne Hubesch said using fuel as a coolant was one of the most promising experimental approaches to the overheating problem.

“Fuels that can absorb heat while powering an aircraft are a key focus for scientists, but this idea relies on heat-consuming chemical reactions that need highly efficient catalysts,” Hubesch said.

“Additionally, the heat exchangers where the fuel comes in contact with the catalysts must be as small as possible, because of the tight volume and weight constraints in hypersonic aircraft.”

To make the new catalysts, the team 3D printed tiny heat exchangers made of metal alloys and coated them with synthetic minerals known as zeolites.

The researchers replicated at lab scale the extreme temperatures and pressures experienced by the fuel at hypersonic speeds, to test the functionality of their design.

Miniature chemical reactors

When the 3D printed structures heat up, some of the metal moves into the zeolite framework- a process crucial to the unprecedented efficiency of the new catalysts.

“Our 3D printed catalysts are like miniature chemical reactors and what makes them so incredibly effective is that mix of metal and synthetic minerals,” Hubesch said.

“It’s an exciting new direction for catalysis, but we need more research to fully understand this process and identify the best combination of metal alloys for the greatest impact.”

The next steps for the research team from RMIT’s Centre for Advanced Materials and Industrial Chemistry (CAMIC) include optimising the 3D printed catalysts by studying them with X-ray synchrotron techniques and other in-depth analysis methods.

The researchers also hope to extend the potential applications of the work into air pollution control for vehicles and miniature devices to improve indoor air quality — especially important in managing airborne respiratory viruses like COVID-19.

CAMIC Director, Distinguished Professor Suresh Bhargava, said the trillion-dollar chemical industry was largely based on old catalytic technology.

“This third generation of catalysis can be linked with 3D printing to create new complex designs that were previously not possible,” Bhargava said.

“Our new 3D printed catalysts represent a radical new approach that has real potential to revolutionise the future of catalysis around the world.”

The 3D printed catalysts were produced using Laser Powder Bed Fusion (L-PBF) technology in the Digital Manufacturing Facility, part of RMIT’s Advanced Manufacturing Precinct.

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Materials provided by RMIT University. Original written by Gosia Kaszubska. Note: Content may be edited for style and length.

Postdoctoral fellow Elizabeth Wallace, a paleotempestologist who joined the lab of Rice climate scientist Sylvia Deethis year, is building upon techniques that reveal the frequency of hurricanes in the Atlantic basin over millennia.

Paleoclimate hurricane data (or ‘proxy’ data) is found in archives like tree rings that retain signs of short-term flooding, sediments in blue holes (marine caverns) and coastal ponds that preserve evidence of sand washed inland by storm surges. These natural archives give researchers a rough idea of when and where hurricanes have come ashore.

In a new paper in Geophysical Research Letters, Wallace, Dee and co-author Kerry Emanuel, a climate scientist at the Massachusetts Institute of Technology, take hundreds of thousands of “synthetic” storms spun up from global climate model simulations of the past 1,000 years and examine whether or not they are captured by the vast network of Atlantic paleohurricane proxies.

Reconstructing the past will help scientists understand the ebb and flow of Atlantic hurricanes over time. Previous studies by Wallace and others have demonstrated that a single site capturing past storms cannot be used to reconstruct hurricane climate changes; however, a network of proxies might help refine models of how these storms are likely to be affected by climate change going forward.

“These paleo hurricane proxies allow us to reconstruct storms into the past, and we’re using them to figure out how basin-wide storm activity has changed,” said Wallace, a Virginia native who earned her doctorate at MIT and the Woods Hole Oceanographic Institution last year and connected with Dee when the professor spoke there in 2017.

“If I have a sediment core from Florida, it’s only capturing storms that hit Florida,” she said. “I wanted to see if we can use the full collection of records collected from the Bahamas, the East Coast and the Gulf of Mexico over the past few decades to accurately reconstruct basin-wide storm activity over the last few centuries.”

The synthetic storms they built helped illustrate what Wallace already knew: There’s a bias toward the Caribbean and Gulf of Mexico, and a need for more proxies along the east coasts of North and Central America. The Rice team’s quest going forward will be to refine their climate simulations and add more sites to the networks to better reconstruct past hurricane activity.

“In particular, there aren’t really any sites from the Southeast U.S., places like the Carolinas,” she said. “One of the goals of this work is to highlight where scientists should go to core next.”

Wallace has first-hand experience drilling cores. “During a storm event, you get high winds and waves that take the sand from the beach and essentially just throw it back into a coastal pond,” she said. “Only during storm events do these sand layers get deposited in the pond, and in the sediment cores you can see them interspersed with the fine mud that’s typically there. We can date these sand layers and know when a hurricane struck the site.”

She noted there has not yet been an “intensive” effort to compare sediment and tree ring records. “The tree record is still an uncertain proxy,” Wallace said. “We’re looking for tree ring records with rainfall signatures that correspond to storms going over the past 200 or 300 years that match the sediment records for that same interval.”

Dee said the work is fundamentally different from the paleoclimate models she most often studies. “Here we’re taking climate models and generating hundreds of pseudo-tropical storms,” she said. “We’re ‘playing Gaia’ by making a plausible version of reality and combining it with our knowledge of available proxy sites.

“This tells us how many records from how many places we realistically need to capture a climate signal,” Dee said. “It’s really expensive to go out and drill cores, and this helps give us a way to prioritize where to drill.

“This research is crucial as we accelerate into a climate mean state with ever-warmer Atlantic Ocean temperatures,” she said. “Understanding how these storms have evolved over time provides a baseline against which to evaluate tropical cyclones with and without human impacts on the climate system.”

A Pan Postdoctoral Research Fellowship and Rice Academy Fellowship to Wallace and a Gulf Research Program grant to Dee supported the study. Dee is an assistant professor of Earth, environmental and planetary sciences. Emanuel is the Cecil & Ida Green Professor of Atmospheric Science and co-director of the Lorenz Center at MIT.