GT/ Solar device for clean water, clean fuel
Energy & green technology biweekly vol.61, 17th November — 5th December
TL;DR
- A floating, solar-powered device that can turn contaminated water or seawater into clean hydrogen fuel and purified water, anywhere in the world, has been developed by researchers.
- Engineers have achieved a world first by manufacturing the first back-contact micrometric photovoltaic cells.
- Bio-based plastics often end up in recycling streams because they look and feel like conventional plastic, but the contamination of these compostable products makes it much harder to generate functional material out of recycled plastic. Scientists have now developed a biology-driven process to convert these mixtures into a new biodegradable material that can be used to make fresh products. The scientists believe the process could also enable a new field of biomanufacturing wherein valuable chemicals and even medicines are made from microbes feeding off of plastic waste.
- Absorbing excess sound to make public environments like theaters and concert halls safer for hearing and using the unwanted sound waves to create electricity is the aim of a new paper. The authors built a system of piezoelectric sensors that can be installed in walls, floors, and ceilings to absorb sound waves and collect their energy. They used computer simulations to fine-tune variables including the voltage needed to power the main device component, the frequency and intensity of the input sound, and piezoelectric sensors tested in parallel and serial configurations.
- A team of researchers has made a significant leap forward in the complex world of molecular chemistry. Azaarenes, unique molecular puzzle pieces crucial to many everyday products, from eco-friendly agrochemicals to essential medicines. The team developed an innovative way to modify these molecules using light-powered enzymes — a groundbreaking discovery that holds promise for new industrially relevant chemical reactions and sustainable energy solutions.
- The researchers developed an algorithm to model how the smaller networks distributed electricity — factoring in how local grids could become unbalanced by adding too many heat pumps in a single area or generating more electricity than the grid could accept.
- The remarkable proton and oxide-ion (dual-ion) conductivities of hexagonal perovskite-related oxide Ba7Nb3.8Mo1.2O20.1 are promising for next-generation electrochemical devices. The unique ion-transport mechanisms they unveiled will hopefully pave the way for better dual-ion conductors, which could play an essential role in tomorrow’s clean energy technologies.
- Researchers have identified the potential environmental risks of using ammonia as a zero-carbon fuel in order to develop an engineering roadmap to a sustainable ammonia economy.
- Exposure to fine particulate air pollutants from coal-fired power plants (coal PM2.5) is associated with a risk of mortality more than double that of exposure to PM2.5 from other sources, according to a new study. Examining Medicare and emissions data in the U.S. from 1999 to 2020, the researchers also found that 460,000 deaths were attributable to coal PM2.5 during the study period — most of them occurring between 1999 and 2007, when coal PM2.5 levels were highest.
- Researchers have used computer models of closed-loop geothermal systems to determine if they would be economically viable sources of renewable energy. They found that the cost of drilling would need to decrease significantly to hit cost targets.
- And more!
Green Technology Market
Green technology is an applicable combination of advanced tools and solutions to conserve natural resources and environment, minimize or mitigate negative impacts from human activities on the environment, and ensure sustainability development. Green technology is also referred to as clean technology or environmental technology which includes technologies, such as IoT, AI, analytics, blockchain, digital twin, security, and cloud, which collect, integrate, and analyze data from various real-time data sources, such as sensors, cameras, and Global Positioning System (GPS).
Green technology, also known as sustainable technology, protects the environment by using various forms of sustainable energy. Some of the best examples of green technologies include solar panels, LED lighting, wind energy, electric vehicles, vertical farming, and composting.
The global Green Technology and Sustainability market size to grow from USD 11.2 billion in 2020 to USD 36.6 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 26.6% during the forecast period. The growing consumer and industrial interest for the use of clean energy resources to conserve environment and increasing use of Radio Frequency Identification sensors across industries are driving the adoption of green technology and sustainability solutions and services in the market.
The blockchain segment is estimated to grow at the highest CAGR: Energy-intensive cryptocurrency mining has caused a spike in carbon emission, and hence blockchain is capable of driving innovation in the field of green technology.
Latest Research
Hybrid photothermal–photocatalyst sheets for solar-driven overall water splitting coupled to water purification
by Pornrungroj, C., Mohamad Annuar, A.B., Wang, Q. et al. in Nature Water
A floating, solar-powered device that can turn contaminated water or seawater into clean hydrogen fuel and purified water, anywhere in the world, has been developed by researchers.
The device, developed by researchers at the University of Cambridge, could be useful in resource-limited or off-grid environments, since it works with any open water source and does not require any outside power.
It takes its inspiration from photosynthesis, the process by which plants convert sunlight into food. However, unlike earlier versions of the ‘artificial leaf’, which could produce green hydrogen fuel from clean water sources, this new device operates from polluted or seawater sources and can produce clean drinking water at the same time. Tests of the device showed it was able to produce clean water from highly polluted water, seawater, and even from the River Cam in central Cambridge.
“Bringing together solar fuels production and water purification in a single device is tricky,” said Dr Chanon Pornrungroj from Cambridge’s Yusuf Hamied Department of Chemistry, the paper’s co-lead author. “Solar-driven water splitting, where water molecules are broken down into hydrogen and oxygen, need to start with totally pure water because any contaminants can poison the catalyst or cause unwanted chemical side-reactions.”
“In remote or developing regions, where clean water is relatively scarce and the infrastructure necessary for water purification is not readily available, water splitting is extremely difficult,” said co-lead author Ariffin Mohamad Annuar. “A device that could work using contaminated water could solve two problems at once: it could split water to make clean fuel, and it could make clean drinking water.”
Pornrungroj and Mohamad Annuar, who are both members of Professor Erwin Reisner’s research group, came up with a design that did just that. They deposited a photocatalyst on a nanostructured carbon mesh that is a good absorber of both light and heat, generating the water vapour used by the photocatalyst to create hydrogen. The porous carbon mesh, treated to repel water, served both to help the photocatalyst float and to keep it away from the water below, so that contaminants do not interfere with its functionality.
In addition, the new device uses more of the Sun’s energy. “The light-driven process for making solar fuels only uses a small portion of the solar spectrum — there’s a whole lot of the spectrum that goes unused,” said Mohamad Annuar. The team used a white, UV-absorbing layer on top of the floating device for hydrogen production via water splitting. The rest of the light in the solar spectrum is transmitted to the bottom of the device, which vaporises the water.
“This way, we’re making better use of the light — we get the vapour for hydrogen production, and the rest is water vapour,” said Pornrungroj. “This way, we’re truly mimicking a real leaf, since we’ve now been able to incorporate the process of transpiration.”
A device that can make clean fuel and clean water at once using solar power alone could help address the energy and the water crises facing so many parts of the world. For example, the indoor air pollution caused by cooking with ‘dirty’ fuels, such as kerosene, is responsible for more than three million deaths annually, according to the World Health Organization. Cooking with green hydrogen instead could help reduce that number significantly. And 1.8 billion people worldwide still lack safe drinking water at home.
“It’s such a simple design as well: in just a few steps, we can build a device that works well on water from a wide variety of sources,” said Mohamad Annuar.
“It’s so tolerant of pollutants, and the floating design allows the substrate to work in very cloudy or muddy water,” said Pornrungroj. “It’s a highly versatile system.”
“Our device is still a proof of principle, but these are the sorts of solutions we will need if we’re going to develop a truly circular economy and sustainable future,” said Reisner, who led the research. “The climate crisis and issues around pollution and health are closely related, and developing an approach that could help address both would be a game-changer for so many people.”
3D interconnects for III-V semiconductor heterostructures for miniaturized power devices
by Mathieu de Lafontaine, Thomas Bidaud, Guillaume Gay, Erwine Pargon, Camille Petit-Etienne, Artur Turala, Romain Stricher, Serge Ecoffey, Maïté Volatier, Abdelatif Jaouad, Christopher E. Valdivia, Karin Hinzer, Simon Fafard, Vincent Aimez, Maxime Darnon in Cell Reports Physical Science
The University of Ottawa, together with national and international partners, has achieved a world first by manufacturing the first back-contact micrometric photovoltaic cells.
The cells, with a size twice the thickness of a strand of hair, have significant advantages over conventional solar technologies, reducing electrode-induced shadowing by 95% and potentially lowering energy production costs by up to three times. The technological breakthrough — led by Mathieu de Lafontaine, a postdoctoral researcher at the University of Ottawa and a part-time physics professor; and Karin Hinzer, vice-dean, research, and University Research Chair in Photonic Devices for Energy at the Faculty of Engineering — paves the way for a new era of miniaturization in the field of electronic devices.
The micrometric photovoltaic cell manufacturing process involved a partnership between the University of Ottawa, the Université de Sherbrooke in Quebec and the Laboratoire des Technologies de la Microélectronique in Grenoble, France.
“These micrometric photovoltaic cells have remarkable characteristics, including an extremely small size and significantly reduced shadowing. Those properties lend themselves to various applications, from densification of electronic devices to areas such as solar cells, lightweight nuclear batteries for space exploration and miniaturization of devices for telecommunications and the internet of things,” Hinzer says.
“This technological breakthrough promises significant benefits for society. Less expensive, more powerful solar cells will help accelerate the energy shift. Lightweight nuclear batteries will facilitate space exploration, and miniaturization of devices will contribute to the growth of the internet of things and lead to more powerful computers and smartphones,” de Lafontaine says.
“The development of these first back-contact micrometric photovoltaic cells is a crucial step in the miniaturization of electronic devices,” he adds.
“Semiconductors are vital in the shift to a carbon-neutral economy. This project is one of many research initiatives that we’re undertaking at the Faculty of Engineering to achieve our societal goals,” says Hinzer. Semiconductors are included in three of the five research areas at the Faculty of Engineering, namely, information technologies, photonics and emerging materials, and two of the four strategic areas of research at the University of Ottawa, namely, creating a sustainable environment and shaping the digital world.
A hybrid chemical-biological approach can upcycle mixed plastic waste with reduced cost and carbon footprint
by Chang Dou, Hemant Choudhary, Zilong Wang, Nawa R. Baral, Mood Mohan, Rolin A. Aguilar, Shenyue Huang, Alexander Holiday, D. Rey Banatao, Seema Singh, Corinne D. Scown, Jay D. Keasling, Blake A. Simmons, Ning Sun in One Earth
Bio-based plastics such as polylactic acid (PLA) were invented to help solve the plastic waste crisis, but they often end up making waste management more challenging. Because these materials look and feel so similar to conventional, petroleum-based plastics, many products end up not in composters, where they break down as designed, but instead get added to the recycling stream by well-intentioned consumers. There, the products get shredded and melted down with the recyclable plastics, bringing down the quality of the mixture and making it harder to manufacture functional products out of recycled plastic resin. The only solution, currently, is to try to separate the different plastics at recycling facilities. Yet even with the most high-end, automated sorting tools, some biobased plastics end up contaminating the sorted streams.
Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) and the Joint BioEnergy Institute (JBEI) are collaborating with X — the moonshot incubator led by Alphabet, Google’s parent company — to not only skip the problematic separation step, but also make the final product better for the planet.
The team has invented a simple “one pot” process to break down mixtures of petroleum-based and bio-based plastics using naturally derived salt solutions paired with specialized microbes. In a single vat, the salts act as a catalyst to break the materials down from polymers, large structures of repeating molecules bonded together, into the individual molecules called monomers, which the microbes then ferment into a new type of biodegradable polymer that can be made into fresh commodity products.
“It’s sort of ironic because the purpose of using bio-based plastics is to be more sustainable, but it’s causing problems,” said first author Chang Dou, a senior scientific engineering associate at the Advanced Biofuels and Bioproducts Process Development Unit (ABPDU) at Berkeley Lab. Dou was recently named as one of the American Institute of Chemical Engineer’s 35 Under 35. “Our project is trying to get around the separation issue and make it so you don’t have to worry about whether you mix your recycling bin. You can put all the plastic in one bucket.”
In addition to streamlining recycling, the team’s approach could enable bio-based manufacturing of other valuable products using the same bacteria that are happily munching on plastic monomers. Imagine a world where biofuels or even medicines could be made from plastic waste — of which there is about 8.3 billion tons sitting around in landfills.
“There is an open discussion on whether we can use waste plastics as a carbon source for biomanufacturing. It is a very advanced idea. But we proved that using waste plastics, we can feed microbes. With more genetic engineering tools, microbes might be able to grow on multiple types of plastics at the same time. We foresee the potential to continue this study where we can replace the sugars, traditional carbon sources for microbes, with the processed hard-to-recycle mixed plastics that can be converted to valuable products through fermentation,” said Zilong Wang, a UC Berkeley postdoctoral researcher working at JBEI.
The Berkeley Lab scientists’ next step is to experiment with other organic salt catalysts to try to find one that is both highly effective at breaking polymers down and can be reused in multiple batches to lower costs. They are also modeling how the process would work at the large scales of real-world recycling facilities.
In their recent paper, the scientists demonstrated the potential of their approach in laboratory bench-scale experiments with mixtures of polyethylene terephthalate (PET) — the most common petroleum-based plastic, used in things like water bottles and spun into polyester fibers — and PLA, the most common bio-based plastic.
They used an amino-acid-based salt catalyst previously developed by colleagues at JBEI and a strain of Pseudomonas putida engineered by scientists at Oak Ridge National Laboratory. This combination successfully broke down 95% of the PET/PLA mixture and converted the molecules into a type of polyhydroxyalkanoate (PHA) polymer. PHAs are a new class of biodegradable plastic substitutes designed to efficiently break down in a variety of natural environments, unlike petroleum-based plastics.
Team member Hemant Choudhary noted that although their chemical recycling process is currently only proven for PET plastics contaminated with biodegradable PLA, it would still be beneficial for the diverse plastic streams encountered in real recycling facilities. “It can be completely integrated with existing plastic sources,” said Choudhary, a Sandia National Laboratories staff scientist working at JBEI. Most commercial products are not just one kind of plastic, but a handful of different kinds combined, he explained. For example, a fleece jacket is made with PET-based polyesters alongside polyolefins or polyamides. “We can throw it in our one-pot process and easily process the polyester component from that mixture and convert it into a bioplastic. These monomers are soluble in water, but the leftover parts, the polyolefins or polyamides, are not.” The leftovers can be easily removed by simple filtration and then sent off for a traditional mechanical recycling process where the material is shredded and melted, said Choudhary.
“Chemical recycling has been a hot topic, but it’s difficult to make it happen at the commercial scale because all the separation steps are so expensive,” said Ning Sun, a staff scientist at the ABPDU, lead author, and principal investigator of this project. “But by using a biocompatible catalyst in water, the microbes can directly convert the depolymerized plastics without extra separation steps. These results are very exciting, although we acknowledge that a number of improvements are still needed to realize the economic viability of the developed process.”
Piezoelectric system on harnessing sound energy in closed environment
by Roshan Zameer Ahmed, Rajendra Prasad P, Mohan Kumar M, Nischith Raj K G, Prajwal Hegde, P Ganesh in Physics of Fluids
The risk of hearing loss does not come just from loud machinery or other obvious noise. It can also affect people in public environments like theaters and concert halls. Absorbing this excess sound to make public environments safer for hearing and using the unwanted sound waves to create electricity is the aim of a paper.
“According to the Centers for Disease Control and Prevention, an estimated 12.5% of children and adolescents aged 6–19 years and 17% of adults aged 20–69 years have suffered permanent damage to their hearing from excessive exposure to noise,” author Rajendra Prasad P said. “Noise above 70 decibels for a prolonged period of time may start to damage our hearing. We need systems that can mitigate really big sounds.”
In their study, the authors focused on enclosed spaces like theaters and concert halls and built a system of piezoelectric sensors that can be installed in the walls, floors, and ceilings to absorb sound waves and collect their energy. Sound waves from loudspeakers in these enclosed spaces is usually between 60 and 100 decibels, sometimes reaching 120 decibels, Prasad said.
“We classified the sound present in closed environments based on the intensity (decibels) that can potentially cause hearing loss,” Prasad said. “Sound energy absorbed using piezoelectric sensors is processed by our system to convert it into electrical energy. Based on the pattern of energy generation, the output of the system is switched between battery and direct harnessed output.”
To design an optimal system for capturing sound waves in enclosed spaces, the authors used computer simulations to fine-tune variables including the voltage needed to power the main device component, the frequency and intensity of the input sound, and piezoelectric sensors tested in parallel and serial configurations.
“The surprising fact is the output of the design is maximum around certain frequencies that align with the frequency and intensity of the sound used in theaters or auditoriums,” Prasad said. “Our design reduces the vibration of sound each time it reflects from the piezoelectric material and reduces the overall sound intensity of the enclosed space.”
In addition to decreasing the risk of hearing loss, the authors wanted to design an energy system that is good for the environment, using a smart power management feature that adjusts depending on how much sound is coming in. It also uses environmentally friendly materials.
“The piezoelectric material we used is a form of quartz, which is nothing more than a mineral composed of silica,” Prasad said. “It is easily biodegradable and also recyclable.”
Remote stereocontrol with azaarenes via enzymatic hydrogen atom transfer
by Maolin Li, Wesley Harrison, Zhengyi Zhang, Yujie Yuan, Huimin Zhao in Nature Chemistry
A team of pioneering researchers from the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI) has made a significant leap forward in the complex world of molecular chemistry.
Their focus? Azaarenes, unique molecular puzzle pieces crucial to many everyday products, from eco-friendly agrochemicals to essential medicines. The CABBI team demonstrated an innovative way to modify these molecules, a groundbreaking discovery that holds promise for new industrially relevant chemical reactions and sustainable energy solutions.
Central to their research is the use of photoenzymatic systems. In simpler terms, it’s akin to supercharging nature’s tiny workers, enzymes, with a flashlight, enabling them to assemble or repair molecular structures in unprecedented ways. By harnessing the power of light, these scientists have unearthed novel chemical reactions that were previously thought to be out of reach. The study was conducted by researchers from the University of Illinois Urbana-Champaign. The lead authors are CABBI Conversion Theme Leader Huimin Zhao, Professor of Chemical and Biomolecular Engineering (ChBE), biosystems design theme leader of the Carl R. Woese Institute for Genomic Biology (IGB), and Director of the NSF Molecule Maker Lab Institute at Illinois; and Maolin Li, a Postdoctoral Research Associate with CABBI, ChBE, and IGB.
Azaarenes, seemingly minuscule in the vast universe of chemistry, nonetheless play a monumental role. They are the building blocks in a plethora of compounds, influencing even the DNA in our cells. But the challenge has always been in their manipulation. Thanks to the team’s development of an ene-reductase system — a specialized molecular toolkit using the ene-reductase enzyme that Zhao’s lab has deployed in previous studies — researchers found a way to intricately modify these molecules without collateral damage.
One of the standout achievements of their work is mastering the enantioselective hydrogen atom transfer. Molecules often come in left- and right-handed versions, or enantiomers, much like gloves. The team’s method allows them to selectively target and adjust either version with unparalleled precision. Moreover, through remote stereo control they could make those precise adjustments from a distance.
For CABBI and the bioenergy sector, this discovery is a game-changer. Biofuels and bioproducts — energy and products derived from plant material instead of non-renewable resources like petroleum — represent a greener and more sustainable future. The team’s research has expanded the range of chemical reactions and bioproducts that can be made efficiently.
The study also introduced the concept of asymmetric photocatalysis, a revolutionary technique that ensures consistency in these reactions. That can open up new avenues for producing biofuels and bioproducts from a broader range of biomass feedstocks, which directly aligns with CABBI’s goals and the broader DOE mission to advance sustainable energy and product solutions.
“With our novel approach to azaarenes and the use of enzymatic hydrogen atom transfer, we’re not just pushing boundaries in chemistry,” Zhao said. “We’re laying down the foundations for a more sustainable and innovative future. Our research has broadened the toolkit available for eco-friendly production and has the potential to catalyze breakthroughs in agrochemicals and beyond.”
Beyond the lab, the potential for real-world applications is immense, from leading the charge in sustainable energy to spearheading safer agricultural chemicals. Advancements in bioenergy and bioproducts can lead to economic growth, with new industries, jobs, and products for consumers and potentially more affordable energy sources. By promoting sustainable and efficient production methods, the research can reduce pollution and environmental degradation, resulting in cleaner air and water for communities. As the world grapples with environmental challenges and the pressing need for sustainable solutions, discoveries like these light the way forward, Li said.
“As a postdoctoral researcher on this project, I’ve been deeply immersed in the intricacies of azaarenes and their potential. Unraveling the challenges of remote stereo control and witnessing the transformative possibilities of our findings has been truly exhilarating. This research isn’t just about the nuances of chemical reactions; it’s about the future of sustainable energy and more. I’m excited to see where this journey takes us next,” Li said.
Discrete optimal designs for distributed energy systems with nonconvex multiphase optimal power flow
by Ishanki De Mel, Oleksiy V. Klymenko, Michael Short in Applied Energy
As power generation from sources like solar and wind increases, along with the introduction of devices such as heat pumps and batteries, a new optimisation tool created at the University of Surrey will help the UK plan for a greener electricity network.
The researchers developed an algorithm to model how these smaller networks distributed electricity — factoring in how local grids could become unbalanced by adding too many heat pumps in a single area or generating more electricity than the grid could accept.
The Surrey team found that it was generally more efficient to generate renewable energy and use it locally, rather than store it in expensive batteries or export it across the grid. By adding data on energy prices, government subsidies and demand to the model, the study could suggest the most efficient way of designing local grids.
Dr Michael Short, Senior Lecturer on Process Systems Engineering at the University of Surrey, said: “Greening the grid is essential, yet it’s an enormous challenge — and it is clear from our modelling that there is no one-size-fits-all approach. Instead, our model shows how local constraints need to be considered when designing new power networks.
“Government now needs to think seriously about whether new subsidies, or even market changes such as pricing electricity differently during off-peak periods, are needed to enable communities to move towards net zero.”
Their model could also suggest the best size of heat pump for a particular setting. In future, this could help households avoid being oversold large appliances, and avoid damaging local grids.
Dr Ishanki De Mel who worked on the project at Surrey said: “Changes in energy prices, the cost of batteries, or government subsidies, can all have large effects on which solutions are best for a particular location. “Our research could help shape Government policy — revealing clearly how effective subsidies and system design can pave the way for net zero initiatives.”
Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides
by Yuichi Sakuda, Taito Murakami, Maxim Avdeev, Kotaro Fujii, Yuta Yasui, James R. Hester, Masato Hagihala, Yoichi Ikeda, Yusuke Nambu, Masatomo Yashima in Chemistry of Materials
The remarkable proton and oxide-ion (dual-ion) conductivities of hexagonal perovskite-related oxide Ba7Nb3.8Mo1.2O20.1 are promising for next-generation electrochemical devices, as reported by scientists at Tokyo Tech. The unique ion-transport mechanisms they unveiled will hopefully pave the way for better dual-ion conductors, which could play an essential role in tomorrow’s clean energy technologies.
Clean energy technologies are the cornerstone of sustainable societies, and solid-oxide fuel cells (SOFCs) and proton ceramic fuel cells (PCFCs) are among the most promising types of electrochemical devices for green power generation. These devices, however, still face challenges that hinder their development and adoption.
Ideally, SOFCs should be operated at low temperatures to prevent unwanted chemical reactions from degrading their constituent materials. Unfortunately, most known oxide-ion conductors, a key component of SOFCs, only exhibit decent ionic conductivity at elevated temperatures. As for PCFCs, not only are they chemically unstable under carbon dioxide atmospheres, but they also require energy-intensive, high-temperature processing steps during manufacture.
Fortunately, there is a type of material that can solve these problems by combining the benefits of both SOFCs and PCFCs: dual-ion conductors. By supporting the diffusion of both protons and oxide ions, dual-ion conductors can realize high total conductivity at lower temperatures and improve the performance of electrochemical devices. Although some perovskite-related dual-ion conducting materials such as Ba7Nb4MoO20 have been reported, their conductivities are not high enough for practical applications, and their underlying conducting mechanisms are not well understood.
After screening various Ba7Nb4-xMo1+xO20+x/2 compositions, the team found that Ba7Nb3.8Mo1.2O20.1 had remarkable proton and oxide-ion conductivities. “Ba7Nb3.8Mo1.2O20.1 exhibited bulk conductivities of 11 mS/cm at 537 ℃ under wet air and 10 mS/cm at 593 ℃ under dry air. Total direct current conductivity at 400 ℃ in wet air of Ba7Nb3.8Mo1.2O20.1 was 13 times higher than that of Ba7Nb4MoO20, and the bulk conductivity in dry air at 306 ℃ is 175 times higher than that of the conventional yttria-stabilized zirconia (YSZ),” highlights Prof. Yashima.
Next, the researchers sought to shed light on the underlying mechanisms behind these high conductivity values. To this end, they conducted ab initio molecular dynamics (AIMD) simulations, neutron diffraction experiments, and neutron scattering length density analyses. These techniques enabled them to study the structure of Ba7Nb3.8Mo1.2O20.1 in greater detail and determine what makes it special as a dual-ion conductor.
Interestingly, the team found that the high oxide-ion conductivity of Ba7Nb3.8Mo1.2O20.1 originates from a unique phenomenon. It turns out that adjacent MO5 monomers in Ba7Nb3.8Mo1.2O20.1 can form M2O9 dimers by sharing an oxygen atom on one of their corners (M = Nb or Mo cation). The breaking and reforming of these dimers gives rise to ultrafast oxide-ion movement in a manner analogous to a long line of people relaying buckets of water (oxide ions) from one person to the next. Furthermore, the AIMD simulations revealed that the observed high proton conduction was due to efficient proton migration in the hexagonal close-packed BaO3 layers in the material.
Taken together, the results of this study highlight the potential of perovskite-related dual-ion conductors and could serve as guidelines for the rational design of these materials. “The present findings of high conductivities and unique ion migration mechanisms in Ba7Nb3.8Mo1.2O20.1 will help the development of science and engineering of oxide-ion, proton, and dual-ion conductors,” concludes a hopeful Prof. Yashima.
Minimizing the impacts of the ammonia economy on the nitrogen cycle and climate
by Matteo B. Bertagni, Robert H. Socolow, John Mark P. Martirez, Emily A. Carter, Chris Greig, Yiguang Ju, Tim Lieuwen, Michael E. Mueller, Sankaran Sundaresan, Rui Wang, Mark A. Zondlo, Amilcare Porporato in Proceedings of the National Academy of Sciences
Ammonia, a main component of many fertilizers, could play a key role in a carbon-free fuel system as a convenient way to transport and store clean hydrogen. The chemical, made of hydrogen and nitrogen (NH3), can also itself be burned as a zero-carbon fuel. However, new research led by Princeton University illustrates that even though it may not be a source of carbon pollution, ammonia’s widespread use in the energy sector could pose a grave risk to the nitrogen cycle and climate without proper engineering precautions.
Publishing their findings, the interdisciplinary team of 12 researchers found that a well-engineered ammonia economy could help the world achieve its decarbonization goals and secure a sustainable energy future. A mismanaged ammonia economy, on the other hand, could ramp up emissions of nitrous oxide (N2O), a long-lived greenhouse gas around 300 times more potent than CO2 and a major contributor to the thinning of the stratospheric ozone layer. It could lead to substantial emissions of nitrogen oxides (NOx), a class of pollutants that contribute to the formation of smog and acid rain. And it could directly leak fugitive ammonia emissions into the environment, also forming air pollutants, impacting water quality, and stressing ecosystems by disturbing the global nitrogen cycle.
Fortunately, the researchers found that the potential negative impacts of an ammonia economy can be minimized with proactive engineering practices. They argued that now is the time to start seriously preparing for an ammonia economy, tackling the potential sticking points of ammonia fuel before its widespread deployment.
“We know an ammonia economy of some scale is likely coming,” said research leader Amilcare Porporato, the Thomas J. Wu ’94 Professor of Civil and Environmental Engineering and the High Meadows Environmental Institute. “And if we are proactive and future-facing in our approach, an ammonia economy could be a great thing. But we cannot afford to take the risks of ammonia lightly. We cannot afford to be sloppy.”
As interest in hydrogen as a zero-carbon fuel has grown, so too has an inconvenient reality: it is notoriously difficult to store and transport over long distances. The tiny molecule must be stored at either temperatures below -253 degrees Celsius or at pressures as high as 700 times atmospheric pressure, conditions that are infeasible for widespread transport and prone to leakage.
Ammonia, on the other hand, is much easier to liquify, transport, and store, capable of being moved around similarly to tanks of propane. Moreover, an established process for converting hydrogen into ammonia has existed since the early 20th century. Known as the Haber-Bosch process, the reaction combines atmospheric nitrogen with hydrogen to form ammonia. While the process was originally developed as a cost-effective way to turn atmospheric nitrogen into ammonia for use in fertilizers, cleaning products, and even explosives, the energy sector has looked to the Haber-Bosch process as a way to store and transport hydrogen fuel in the form of ammonia.
Ammonia synthesis is inherently energy-intensive, and fossil fuels without CO2 capture are currently used to meet almost all of its feedstock and energy demands. But as the researchers pointed out in their article, if new, electricity-driven processes that are currently under development can replace conventional fossil-fuel-derived ammonia synthesis, then the Haber-Bosch process — or a different process altogether — could be widely used to convert clean hydrogen into ammonia, which can itself be burned as a zero-carbon fuel.
“Ammonia is an easy way to transport hydrogen over long distances, and its widespread use in agriculture means there is already an established infrastructure for producing and moving ammonia,” said Matteo Bertagni, postdoctoral researcher at the High Meadows Environmental Institute working on the Carbon Mitigation Initiative. “You could therefore create hydrogen in a resource-rich area, transform it into ammonia, and then transport it anywhere it’s needed around the globe.”
Ammonia’s transportability is especially attractive to industries reliant on long-distance transportation, such as maritime shipping, and countries with limited available space for renewable resources. Japan, for example, already has a national energy strategy in place that incorporates the use of ammonia as a clean fuel. Straightforward storage requirements mean that ammonia might also find use as a vessel for long-term energy storage, complementary to or even replacing batteries.
“At first glance, ammonia seems like an ideal cure for the problem of decarbonization,” Porporato said. “But almost every medicine comes with a set of potential side effects.”
In theory, burning ammonia should yield only harmless nitrogen gas (N2) and water as products. But in practice, Michael E. Mueller, associate chair and professor of mechanical and aerospace engineering, stated that ammonia combustion can release harmful NOx and N2O pollutants. Most N2O emissions from ammonia combustion are the result of disruptions to the combustion process. “N2O is essentially an intermediate species in the combustion process,” Mueller said. “If the combustion process is allowed to finish, then there will be essentially no N2O emissions.”
Yet Mueller said that under certain conditions, such as when a turbine is ramping up or down or if the hot combustion gases impinge upon cold walls, the ammonia combustion process can become disrupted and N2O emissions can quickly accumulate.
For instance, the researchers found that if ammonia fuel achieves a market penetration equal to around 5% of the current global primary energy demand (which would require 1.6 billion metric tons of ammonia production, or ten times current production levels), and if 1% of the nitrogen in that ammonia is lost as N2O, then ammonia combustion could produce greenhouse gas emissions equivalent to 15% of today’s emissions from fossil fuels. The greenhouse gas intensity of such a loss rate would mean that burning ammonia fuel would be more polluting than coal.
Like ammonia’s N2O emissions, Robert Socolow, a professor of mechanical and aerospace engineering, emeritus, and senior scholar at Princeton, said that widespread usage of ammonia in the energy sector will add to all the other impacts that fertilizer has already had on the global nitrogen cycle.
In a seminal paper published in 1999, Socolow discussed the environmental impacts of the food system’s widespread use of nitrogen-enriched fertilizers to promote crop growth, writing that, “Excess fixed nitrogen, in various guises, augments the greenhouse effect…contaminates drinking water, acidifies rain…and stresses ecosystems.”
As the energy sector looks toward ammonia as a fuel, Socolow said that it can learn from agriculture’s use of ammonia as a fertilizer. He urged those in the energy sector to consult the decades of work from ecologists and agricultural scientists to understand the role of excess nitrogen in disturbing natural systems.
“Ammonia fuel can be done, but it cannot be done in any way we wish,” said Socolow, whose 2004 paper with Stephen Pacala, the Frederick D. Petrie Professor in Ecology and Evolutionary Biology, emeritus, on stabilization wedges has become a foundation of modern climate policy. “It’s important that we look before we leap.”
While the environmental consequences of an ammonia economy gone wrong are serious, the researchers emphasized that the potential stumbling blocks they identified are solvable through proactive engineering.
“I interpret this paper as a handbook for engineers,” Mueller said. “By identifying the worst-case scenario for an ammonia economy, we’re really identifying what we need to be aware of as we develop, design, and optimize new ammonia-based energy systems.”
For instance, Mueller said there are alternative combustion strategies that could help to minimize unwanted NOx and N2O emissions. While each strategy has its own set of pros and cons, he said that taking the time now to evaluate candidate systems with an eye toward mitigating emissions will ensure that combustion systems are poised to operate optimally for ammonia fuel. Another option for accessing the energy in ammonia involves partially or fully splitting ammonia back into hydrogen and atmospheric nitrogen through a process known as cracking. Ammonia cracking, a line of research being actively pursued by Emily A. Carter, could help to make the fuel composition more favorable for combustion or even bypass the environmental concerns of ammonia burning by regenerating hydrogen fuel at the point of use. Carter is the Gerhard R. Andlinger Professor of Energy and the Environment and senior strategic advisor and associate laboratory director for applied materials and sustainability sciences at the Princeton Plasma Physics Laboratory (PPPL).
Furthermore, several technologies already exist at the industrial scale to convert unwanted NOx emissions from combustion back into N2 through a process known as selective catalytic reduction. These technologies could be straightforward to transfer to ammonia-based fuel applications. And as a convenient bonus, many of them rely on ammonia as a feedstock to remove NOx — something that there would already be plenty of in an ammonia-based system.
Beyond the engineering practices that could be developed to minimize the environmental impacts of an ammonia economy, Porporato said future work will also look beyond engineering approaches to identify policies and regulatory strategies that would ensure the best-case scenario for ammonia fuel.
“Imagine the problems we could have avoided if we knew the risks and environmental impacts of burning fossil fuels before the Industrial Revolution began,” Porporato said. “With the ammonia economy, we have the chance to learn from our carbon-emitting past. We have the opportunity to solve the challenges we’ve identified before they become an issue in the real world.”
Mortality risk from United States coal electricity generation
by Lucas Henneman, Christine Choirat, Irene Dedoussi, Francesca Dominici, Jessica Roberts, Corwin Zigler in Science
Exposure to fine particulate air pollutants from coal-fired power plants (coal PM2.5) is associated with a risk of mortality more than double that of exposure to PM2.5 from other sources, according to a new study led by George Mason University, The University of Texas at Austin, and Harvard T.H. Chan School of Public Health. Examining Medicare and emissions data in the U.S. from 1999 to 2020, the researchers also found that 460,000 deaths were attributable to coal PM2.5 during the study period — most of them occurring between 1999 and 2007, when coal PM2.5 levels were highest.
While previous studies have quantified the mortality burden from coal-fired power plants, much of this research has assumed that coal PM2.5 has the same toxicity as PM2.5 from other sources.
“PM2.5 from coal has been treated as if it’s just another air pollutant. But it’s much more harmful than we thought, and its mortality burden has been seriously underestimated,” said lead author Lucas Henneman, assistant professor in the Sid and Reva Dewberry Department of Civil, Environmental, and Infrastructure Engineering at Mason. “These findings can help policymakers and regulators identify cost-effective solutions for cleaning up the country’s air, for example, by requiring emissions controls or encouraging utilities to use other energy sources, like renewables.”
Using emissions data from 480 coal power plants in the U.S. between 1999 and 2020, the researchers modeled where wind carried coal sulfur dioxide throughout the week after it was emitted and how atmospheric processes converted the sulfur dioxide into PM2.5. This model produced annual coal PM2.5 exposure fields for each power plant. They then examined individual-level Medicare records from 1999 to 2016, representing the health statuses of Americans ages 65 and older and representing a total of more than 650 million person-years. By linking the exposure fields to the Medicare records, inclusive of where enrollees lived and when they died, the researchers were able to understand individuals’ exposure to coal PM2.5 and calculate the impact it had on their health.
They found that across the U.S. in 1999, the average level of coal PM2.5 was 2.34 micrograms per cubic meter of air (μg/m3). This level decreased significantly by 2020, to 0.07 μg/m3. The researchers calculated that a one μg/m3 increase in annual average coal PM2.5 was associated with a 1.12% increase in all-cause mortality, a risk 2.1 times greater than that of PM2.5 from any other source. They also found that 460,000 deaths were attributable to coal PM2.5, representing 25% of all PM2.5-related deaths among Medicare enrollees before 2009.
The researchers were also able to quantify deaths attributable to specific power plants, producing a ranking of the coal-fired power plants studied based on their contribution to coal PM2.5’s mortality burden. They found that 10 of these plants each contributed at least 5,000 deaths during the study period.
The study also found that 390,000 of the 460,000 deaths attributable to coal-fired power plants took place between 1999 and 2007, averaging more than 43,000 deaths per year. After 2007, these deaths declined drastically, to an annual total of 1,600 by 2020.
“Beyond showing just how harmful coal pollution has been, we also show good news: Deaths from coal were highest in 1999 but by 2020 decreased by about 95%, as coal plants have installed scrubbers or shut down,” Henneman said.
“I see this as a success story,” added senior author Corwin Zigler, associate professor in the Department of Statistics and Data Sciences at UT Austin and founding member of the UT Center for Health & Environment: Education & Research. “Coal power plants were this major burden that U.S. policies have already significantly reduced. But we haven’t completely eliminated the burden — so this study provides us a better understanding of how health will continue to improve and lives will be saved if we move further toward a clean energy future.”
The researchers pointed out the study’s continuing urgency and relevance, writing in the paper that coal power is still part of some U.S. states’ energy portfolios and that global coal use for electricity generation is even projected to increase.
“As countries debate their energy sources — and as coal maintains a powerful, almost mythical status in American energy lore — our findings are highly valuable to policymakers and regulators as they weigh the need for cheap energy with the significant environmental and health costs,” said co-author Francesca Dominici, Clarence James Gamble Professor of Biostatistics, Population, and Data Science at Harvard Chan School and director of the Harvard Data Science Initiative.
Numerical investigation of closed-loop geothermal systems in deep geothermal reservoirs
by Mark White, Yaroslav Vasyliv, Koenraad Beckers, Mario Martinez, Paolo Balestra, Carlo Parisi, Chad Augustine, Gabriela Bran-Anleu, Roland Horne, Laura Pauley, Giorgia Bettin, Theron Marshall, Anastasia Bernat in Geothermics
Geothermal power has a lot of promise as a renewable energy source that is not dependent on the sun shining or the wind blowing, but it has some challenges to wide adoption. One of these challenges is that there are a limited number of locations in the U.S. that naturally have the right conditions: hot rock relatively close to the surface and with plentiful groundwater to heat up.
Closed-loop geothermal is one way to use hot, dry rock to heat up circulating fluids to generate electricity or to directly heat buildings, a way that is being reexamined after being dismissed in the ’80s for being too inefficient. A team composed of experts at several national laboratories has recently finished a two-year effort to computationally model closed-loop geothermal systems. One of the key challenges with closed-loop geothermal is building a system that can extract enough heat from the deep earth to be cost-effective, said Mario Martinez, a mechanical engineer and the principal investigator for the project at Sandia National Laboratories.
“The subsurface, the rock, becomes hotter the deeper you go, so it is beneficial to go deep,” said Martinez, who recently retired. “That hot water can be used for district heating, so you can use it to heat houses and buildings, or you can use it to generate electricity.”
Sandia led the computational modeling of the belowground system, while the National Renewable Energy Laboratory used the numerical results to estimate the economic viability of the system through their aboveground power plant and economic model. The overall project was led by Pacific Northwest National Laboratory and mechanical engineer Mark White. Anastasia Bernat, a PNNL data scientist, integrated the Sandia and NREL models into a publicly available web tool to allow start-up developers and venture capitalists to explore the economic viability of various closed-loop geothermal system designs. Idaho National Laboratory shared variables from a prototype geothermal system at the lab and studied various possible enhancements to closed-loop geothermal systems to improve their economic viability.
The Sandia team looked at two basic setups for closed-loop geothermal systems. One, called a U-tube, is where cool water is pumped down one deep vertical pipe, which then extends horizontally for a certain distance at a depth where the rock is hot and then comes up in a different location, Martinez said. The other, called a tube-in-a-tube, is where the cool water is pumped down along the outer layer of a pipe to a certain depth, and then the pipe takes a 90-degree turn and extends a horizontal distance at that depth. Then the hot water hits the end of the pipe and is pushed into the inner pipe, back up the way it came.
The Sandia team looked at depths ranging from 0.6 miles to slightly over 3 miles, as well as the distance traveled at that depth from 0.6 miles to almost 12.5 miles. They looked at several different factors, one of which was whether to circulate water or supercritical carbon dioxide, a gas that is under so much pressure it acts more like a liquid and can absorb more heat, Martinez said.
They also looked at the temperature of the fluid going down the well and how fast the fluid was being pumped down. Other parameters they studied included how quickly the rock heated up with depth, how well the rock transferred heat to the circulating fluid in the pipe, and how large the pipe diameter is. The Sandia team used an engineering mechanics simulation software package called Sierra and parametric analysis software Dakota to look at all the different parameters, said Yaro Vasyliv, a Sandia computer scientist who develops Sierra codes and was involved in this project.
“We varied seven parameters and computed corresponding outlet temperatures and pressures,” Vasyliv said. “You can feed that into an aboveground model that computes the levelized cost of heat and the levelized cost of electricity, which is what NREL worked on.”
Using a simplified numerical model instead of a full 3D representation, and running the computations on Sandia’s high-performance computing clusters, allowed the researchers to model several million sets of parameters, Martinez said.
“Part of the novelty of this work is that we could analyze so many different cases, so many different parameters for those two fluids and those two designs — the U-tube and the tube-in-a-tube,” he said.
The Sandia researchers also did more time-intensive models of geothermal systems in permeable rock with groundwater, where the additional convective heat transfer would produce a more rapid and sustained transfer of heat from the rock to the circulating fluid. They found that this increased heat transfer also improved the economic viability of a closed-loop geothermal system.
“Wet rock is better, and it can be quite a bit better, but there aren’t many places that naturally have those conditions,” Martinez said.
The Sandia researchers looked at several possible enhancements to the system, such as coating the well with high-thermal-conductivity cement. They found that it would be better to just make the pipe larger, Martinez said. They also found that their model could approximate the efficiency of a multi-pronged or “spider” geothermal configuration by merely setting the horizontal extent in the tool to the total extent of all the legs, Martinez said.
“We asked the question, ‘what is the drilling cost required to meet DOE’s 2035 target for the levelized cost of electricity for enhanced geothermal systems?’” Vasyliv said. “This target is $45 per megawatt-hour. We found that to achieve this goal using closed-loop systems in hot, dry rock, there would need to be a very aggressive reduction in the cost of drilling.”
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