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      in Energy

      MIT engineers devise technology to prevent fouling in photobioreactors for CO2 capture

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      Algae grown in transparent tanks or tubes supplied with carbon dioxide can convert the greenhouse gas into other compounds, such as food supplements or fuels. But the process leads to a buildup of algae on the surfaces that clouds them and reduces efficiency, requiring laborious cleanout procedures every couple of weeks.

      MIT researchers have come up with a simple and inexpensive technology that could substantially limit this fouling, potentially allowing for a much more efficient and economical way of converting the unwanted greenhouse gas into useful products.

      The key is to coat the transparent containers with a material that can hold an electrostatic charge, and then applying a very small voltage to that layer. The system has worked well in lab-scale tests, and with further development might be applied to commercial production within a few years.

      The findings are being reported in the journal Advanced Functional Materials, in a paper by recent MIT graduate Victor Leon PhD ’23, professor of mechanical engineering Kripa Varanasi, former postdoc Baptiste Blanc, and undergraduate student Sophia Sonnert.

      No matter how successful efforts to reduce or eliminate carbon emissions may be, there will still be excess greenhouse gases that will remain in the atmosphere for centuries to come, continuing to affect global climate, Varanasi points out. “There’s already a lot of carbon dioxide there, so we have to look at negative emissions technologies as well,” he says, referring to ways of removing the greenhouse gas from the air or oceans, or from their sources before they get released into the air in the first place.

      When people think of biological approaches to carbon dioxide reduction, the first thought is usually of planting or protecting trees, which are indeed a crucial “sink” for atmospheric carbon. But there are others. “Marine algae account for about 50 percent of global carbon dioxide absorbed today on Earth,” Varanasi says. These algae grow anywhere from 10 to 50 times more quickly than land-based plants, and they can be grown in ponds or tanks that take up only a tenth of the land footprint of terrestrial plants.

      What’s more, the algae themselves can then be a useful product. “These algae are rich in proteins, vitamins and other nutrients,” Varanasi says, noting they could produce far more nutritional output per unit of land used than some traditional agricultural crops.

      If attached to the flue gas output of a coal or gas power plant, algae could not only thrive on the carbon dioxide as a nutrient source, but some of the microalgae species could also consume the associated nitrogen and sulfur oxides present in these emissions. “For every two or three kilograms of CO2, a kilogram of algae could be produced, and these could be used as biofuels, or for Omega-3, or food,” Varanasi says.

      Omega-3 fatty acids are a widely used food supplement, as they are an essential part of cell membranes and other tissues but cannot be made by the body and must be obtained from food. “Omega 3 is particularly attractive because it’s also a much higher-value product,” Varanasi says.

      Most algae grown commercially are cultivated in shallow ponds, while others are grown in transparent tubes called photobioreactors. The tubes can produce seven to 10 times greater yields than ponds for a given amount of land, but they face a major problem: The algae tend to build up on the transparent surfaces, requiring frequent shutdowns of the whole production system for cleaning, which can take as long as the productive part of the cycle, thus cutting overall output in half and adding to operational costs.

      The fouling also limits the design of the system. The tubes can’t be too small because the fouling would begin to block the flow of water through the bioreactor and require higher pumping rates.

      Varanasi and his team decided to try to use a natural characteristic of the algae cells to defend against fouling. Because the cells naturally carry a small negative electric charge on their membrane surface, the team figured that electrostatic repulsion could be used to push them away.

      The idea was to create a negative charge on the vessel walls, such that the electric field forces the algae cells away from the walls. To create such an electric field requires a high-performance dielectric material, which is an electrical insulator with a high “permittivity” that can produce a large change in surface charge with a smaller voltage.

      “What people have done before with applying voltage [to bioreactors] has been with conductive surfaces,” Leon explains, “but what we’re doing here is specifically with nonconductive surfaces.”

      He adds: “If it’s conductive, then you pass current and you’re kind of shocking the cells. What we’re trying to do is pure electrostatic repulsion, so the surface would be negative and the cell is negative so you get repulsion. Another way to describe it is like a force field, whereas before the cells were touching the surface and getting shocked.”

      The team worked with two different dielectric materials, silicon dioxide — essentially glass — and hafnia (hafnium oxide), both of which turned out to be far more efficient at minimizing fouling than conventional plastics used to make photobioreactors. The material can be applied in a coating that is vanishingly thin, just 10 to 20 nanometers (billionths of a meter) thick, so very little would be needed to coat a full photobioreactor system.

      “What we are excited about here is that we are able to show that purely from electrostatic interactions, we are able to control cell adhesion,” Varanasi says. “It’s almost like an on-off switch, to be able to do this.”

      Additionally, Leon says, “Since we’re using this electrostatic force, we don’t really expect it to be cell-specific, and we think there’s potential for applying it with other cells than just algae. In future work, we’d like to try using it with mammalian cells, bacteria, yeast, and so on.” It could also be used with other valuable types of algae, such as spirulina, that are widely used as food supplements.

      The same system could be used to either repel or attract cells by just reversing the voltage, depending on the particular application. Instead of algae, a similar setup might be used with human cells to produce artificial organs by producing a scaffold that could be charged to attract the cells into the right configuration, Varanasi suggests.

      “Our study basically solves this major problem of biofouling, which has been a bottleneck for photobioreactors,” he says. “With this technology, we can now really achieve the full potential” of such systems, although further development will be needed to scale up to practical, commercial systems.

      As for how soon this could be ready for widespread deployment, he says, “I don’t see why not in three years’ timeframe, if we get the right resources to be able to take this work forward.”

      The study was supported by energy company Eni S.p.A., through the MIT Energy Initiative. More

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      in Security

      Scientists uncover the amazing way sandgrouse hold water in their feathers

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      Many birds’ feathers are remarkably efficient at shedding water — so much so that “like water off a duck’s back” is a common expression. Much more unusual are the belly feathers of the sandgrouse, especially Namaqua sandgrouse, which absorb and retain water so efficiently the male birds can fly more than 20 kilometers from a distant watering hole back to the nest and still retain enough water in their feathers for the chicks to drink and sustain themselves in the searing deserts of Namibia, Botswana, and South Africa.

      How do those feathers work? While scientists had inferred a rough picture, it took the latest tools of microscopy, and patient work with a collection of sandgrouse feathers, to unlock the unique structural details that enable the feathers to hold water. The findings appear today in the Journal of the Royal Society Interface, in a paper by Lorna Gibson, the Matoula S. Salapatas Professor of Materials Science and Engineering and a professor of mechanical engineering at MIT, and Professor Jochen Mueller of Johns Hopkins University.

      The unique water-carrying ability of sandgrouse feathers was first reported back in 1896, Gibson says, by E.G.B. Meade-Waldo, who was breeding the birds in captivity. “He saw them behaving like this, and nobody believed him! I mean, it just sounded so outlandish,” Gibson says.

      In 1967, Tom Cade and Gordon MacLean reported detailed observations of the birds at watering holes, in a study that proved the unique behavior was indeed real. The scientists found that male sandgrouse feathers could hold about 25 milliliters of water, or about a tenth of a cup, after the bird had spent about five minutes dipping in the water and fluffing its feathers.

      About half of that amount can evaporate during the male bird’s half-hour-long flight back to the nest, where the chicks, which cannot fly for about their first month, drink the remainder straight from the feathers.

      Cade and MacLean “had part of the story,” Gibson says, but the tools didn’t exist at the time to carry out the detailed imaging of the feather structures that the new study was able to do.

      Gibson and Mueller carried out their study using scanning electron microscopy, micro-computed tomography, and video imaging. They borrowed Namaqua sandgrouse belly feathers from Harvard University’s Museum of Comparative Zoology, which has a collection of specimens of about 80 percent of the world’s birds.

      Bird feathers in general have a central shaft, from which smaller barbs extend, and then smaller barbules extend out from those. Sandgrouse feathers are structured differently, however. In the inner zone of the feather, the barbules have a helically coiled structure close to their base and then a straight extension. In the outer zone of the feather, the barbules lack the helical coil and are simply straight. Both parts lack the grooves and hooks that hold the vane of contour feathers together in most other birds.
      Video of water spreading through the specialized sandgrouse feathers, under magnification, shows the uncoiling and spreading of the feather’s barbules as they become wet. Initially, most barbules in the outer zone of the feather form tubular features.Credit: Specimen #142928, Museum of Comparative Zoology, Harvard University © President and Fellows of Harvard College.

      When wetted, the coiled portions of the barbules unwind and rotate to be perpendicular to the vane, producing a dense forest of fibers that can hold water through capillary action. At the same time, the barbules in the outer zone curl inward, helping to hold the water in.

      The microscopy techniques used in the new study allowed the dimensions of the different parts of the feather to be measured. In the inner zone, the barb shafts are large and stiff enough to provide a rigid base about which the other parts of the feather deform, and the barbules are small and flexible enough that surface tension is sufficient to bend the straight extensions into tear-like structures that hold water. And in the outer zone, the barb shafts and barbules are smaller still, allowing them to curl around the inner zone, further retaining water.

      While previous work had suggested that surface tension produced the water retention characteristics, “what we did was make measurements of the dimensions and do some calculations to show that that’s what is actually happening,” Gibson says. Her group’s work demonstrated that the varying stiffnesses of the different feather parts plays a key role in their ability to hold water.

      The study was mostly driven by intellectual curiosity about this unique behavioral phenomenon, Gibson says. “We just wanted to see how it works. The whole story just seemed so interesting.” But she says it might lead to some useful applications. For example, in desert regions where water is scarce but fog and dew regularly occur, such as in Chile’s Atacama Desert, some adaptation of this feather structure might be incorporated into the systems of huge nets that are used to collect water. “You could imagine this could be a way to improve those systems,” she says. “A material with this kind of structure might be more effective at fog harvesting and holding the water.”

      “This fascinating and in-depth study reveals how the different parts of the sandgrouse’s belly feathers — including the microscopic barb shafts and barbules — work together to hold water,” says Mary Caswell Stoddard, an evolutionary biologist at Princeton University, who was not associated with this study. “By using a suite of advanced imaging techniques to describe the belly feathers and estimate their bending stiffnesses, Mueller and Gibson add rich new details to our understanding of the sandgrouse’s water-carrying feathers. … This study may inspire others to take a closer look at diverse feather microstructures across bird species — and to wonder whether these structures, as in sandgrouse, help support unusual or surprising functions.”

      The work was partly supported by the National Science Foundation and the Matoula S. Salapatas Professorship in Materials Science and Engineering at MIT. More

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      in Environment

      A new microneedle-based drug delivery technique for plants

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      Increasing environmental conditions caused by climate change, an ever-growing human population, scarcity of arable land, and limited resources are pressuring the agriculture industry to adopt more sustainable and precise practices that foster more efficient use of resources (e.g., water, fertilizers, and pesticides) and mitigation of environmental impacts. Developing delivery systems that efficiently deploy agrochemicals such as micronutrients, pesticides, and antibiotics in crops will help ensure high productivity and high produce quality, while minimizing the waste of resources, is crucial.

      Now, researchers in Singapore and the U.S. have developed the first-ever microneedle-based drug delivery technique for plants. The method can be used to precisely deliver controlled amounts of agrochemicals to specific plant tissues for research purposes. When applied in the field, it could one day be used in precision agriculture to improve crop quality and disease management.

      The work is led by researchers from the Disruptive and Sustainable Technologies for Agricultural Precision (DiSTAP) interdisciplinary research group at the Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise in Singapore, and their collaborators from MIT and the Temasek Life Sciences Laboratory (TLL).

      Current and standard practices for agrochemical application in plants, such as foliar spray, are inefficient due to off-target application, quick runoff in the rain, and actives’ rapid degradation. These practices also cause significant detrimental environmental side effects, such as water and soil contamination, biodiversity loss, and degraded ecosystems; and public health concerns, such as respiratory problems, chemical exposure, and food contamination.

      The novel silk-based microneedles technique circumvents these limitations by deploying and targeting a known amount of payload directly into a plant’s deep tissues, which will lead to higher efficacy of plant growth and help with disease management. The technique is minimally invasive, as it delivers the compound without causing long-term damage to the plants, and is environmentally sustainable. It minimizes resource wastage and mitigates the adverse side effects caused by agrochemical contamination of the environment. Additionally, it will help foster precise agricultural practices and provide new tools to study plants and design crop traits, helping to ensure food security.

      Described in a paper titled “Drug Delivery in Plants Using Silk Microneedles,” published in a recent issue of Advanced Materials, the research studies the first-ever polymeric microneedles used to deliver small compounds to a wide variety of plants and the plant response to biomaterial injection. Through gene expression analysis, the researchers could closely examine the reactions to drug delivery following microneedle injection. Minimal scar and callus formation were observed, suggesting minimal injection-induced wounding to the plant. The proof of concept provided in this study opens the door to plant microneedles’ application in plant biology and agriculture, enabling new means to regulate plant physiology and study metabolisms via efficient and effective delivery of payloads.

      The study optimized the design of microneedles to target the systemic transport system in Arabidopsis (mouse-ear cress), the chosen model plant. Gibberellic acid (GA3), a widely used plant growth regulator in agriculture, was selected for the delivery. The researchers found that delivering GA3 through microneedles was more effective in promoting growth than traditional methods (such as foliar spray). They then confirmed the effectiveness using genetic methods and demonstrated that the technique is applicable to various plant species, including vegetables, cereals, soybeans, and rice.

      Professor Benedetto Marelli, co-corresponding author of the paper, principal investigator at DiSTAP, and associate professor of civil and environmental engineering at MIT, shares, “The technique saves resources as compared to current methods of agrochemical delivery, which suffer from wastage. During the application, the microneedles break through the tissue barriers and release compounds directly inside the plants, avoiding agrochemical losses. The technique also allows for precise control of the amounts of the agrochemical used, ensuring high-tech precision agriculture and crop growth to optimize yield.”

      “The first-of-its-kind technique is revolutionary for the agriculture industry. It also minimizes resource wastage and environmental contamination. In the future, with automated microneedle application as a possibility, the technique may be used in high-tech outdoor and indoor farms for precise agrochemical delivery and disease management,” adds Yunteng Cao, the first author of the paper and postdoc at MIT.

      “This work also highlights the importance of using genetic tools to study plant responses to biomaterials. Analyzing these responses at the genetic level offers a comprehensive understanding of these responses, thereby serving as a guide for the development of future biomaterials that can be used across the agri-food industry,” says Sally Koh, the co-first author of this work and PhD candidate from NUS and TLL.

      The future seems promising as Professor Daisuke Urano, co-corresponding author of the paper, TLL principal investigator, and NUS adjunct assistant professor elaborates, “Our research has validated the use of silk-based microneedles for agrochemical application, and we look forward to further developing the technique and microneedle design into a scalable model for manufacturing and commercialization. At the same time, we are also actively investigating potential applications that could have a significant impact on society.”

      The study of drug delivery in plants using silk microneedles expanded upon previous research supervised by Marelli. The original idea was conceived by SMART and MIT: Marelli, Cao, and Professor Nam-Hai Chua, co-lead principal investigator at DiSTAP. Researchers from TLL and the National University of Singapore, Professor Urano Daisuke and Koh, joined the study to contribute biological perspectives. The research is carried out by SMART and supported by the National Research Foundation Singapore (NRF) under its Campus for Research Excellence And Technological Enterprise (CREATE) program.

      SMART was established by MIT and NRF in 2007. SMART is the first entity in CREATE, developed by NRF. SMART serves as an intellectual and innovation hub for research interactions between MIT and Singapore, undertaking cutting-edge research in areas of interest to both parties. SMART currently comprises an Innovation Center and interdisciplinary research groups: Antimicrobial Resistance, Critical Analytics for Manufacturing Personalized-Medicine, DiSTAP, Future Urban Mobility, and Low Energy Electronic Systems. More

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      in Energy

      Responding to Ukraine’s “ocean of suffering”

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      Within 72 hours of the first Russian missiles striking Kyiv, Ukraine, in February 2022, Ian Miller SM ’19 boarded a flight for Poland.

      Later, he’d say he felt motivated by Kyiv’s “tragic ocean of suffering” and Ukrainian President Zelensky’s pleas for help. But he arrived with little notion of what to do.

      As he’d anticipated, his hotel in Rzeszów turned out to be a hub for aid workers and journalists. Miller was on his laptop, using the lobby Wi-Fi to work remotely as an MIT Energy Initiative (MITEI) project manager, when he overheard a reporter interviewing a Finnish man about his efforts to get bulletproof vests and helmets to the front lines.

      Miller soon found himself loading supplies onto trains that had brought huge numbers of refugees — mostly women, children, and the elderly — to the station in Rzeszów. The trains ran back at night, their empty seats filled with medical supplies, generators, and baby food, their lights dimmed to reduce the chances of attack.

      In April 2022, Miller and volunteers from a half-dozen countries planned and drove a convoy of trucks packed with tourniquets, bandages, and bulletproof vests across the border, arriving at the site of the Bucha massacre soon after the Russians retreated.

      Miller peered into a mass grave. “They were still excavating it, and those weren’t soldiers, you know?” he says. “I try to avoid looking at things like that too often, because it doesn’t help us save lives to be horrified all the time.” He downplays any potential danger to himself, telling his family he’s safer where he is than in parts of the United States.

      Soon after his first trip across the border, Miller convinced his former MIT roommate, Evan Platt SM ’20, to come help. “Just for a week,” he told Platt.

      Inspired by energy

      Miller and Platt met in 2008 in Washington, where Platt was interning at the White House and Miller was about to start his senior year at Georgetown University.

      Miller majored in government, but his interest in energy policy and technology grew during the years after graduation he spent teaching science to primary and secondary school students in New York, where he’d grown up; in Boston; and in Kampala, Uganda. “Some of the most fun, inspiring, engaging lessons and modules I did with the kids were focused on energy,” he recalls.

      While pursuing an MIT master of science in chemical engineering from 2016 to 2018, he started researching photovoltaics and wind power. He held leadership positions with the MIT Energy Conference and the MIT Energy Club.

      After joining MITEI, Miller worked on electric vehicles (EVs), EV charging patterns, and other applications. He became project manager and research specialist for the Sustainable Energy System Analysis Modeling Environment (SESAME), which models the levels of greenhouse gas emissions from multiple energy sectors in future scenarios.

      Miller and Platt reconnected and shared an apartment for three years. Platt studied systems design and management through a joint MIT School of Engineering and Sloan School of Management program, then stayed on to work for the MIT Technology Licensing Office.

      Platt left MIT to pursue other interests in 2020. The next time the two would see each other would be in Poland.

      “It’s not easy living and working in an active combat zone,” Platt says. “There is nobody on Earth I would rather be navigating this environment with than Ian.”

      Navigating the last mile

      In Rzeszów and Ukraine, Miller and U.S. Air Force veteran Mark Lindquist oversaw fulfillment for the new team. With the help of Google Translate, their phones lit up with encrypted texts to and from Polish customs agents and Ukrainian warehouse operators.

      Platt and two Ukrainian team members took the lead on a needs analysis of what was most in demand at the front. Another team member led procurement. Their efforts crystallized in the creation of Zero Line, a tax-exempt nonprofit that works closely with the Ukrainian government at the front line (a.k.a. “the zero line”).

      With Platt on board, “we got more rigorous and quantitative in terms of lives-saved-per-dollar,” Miller says. A hundred dollars buys four tourniquets. A thousand dollars adds crude steel armor to a Jeep. Two thousand dollars provides a small observation drone or a satellite phone, equipment that locates Russian artillery and detects Russian attacks.

      “Russian artillery shells are the No. 1 killer of Ukrainians, causing around 80 percent of casualties,” he says. “Tourniquets save people injured by Russian shells, vehicles help evacuate them, and communications equipment prevents deadly injuries from occurring in the first place.”

      Miller’s skills in transportation and power system modeling, developed at MITEI under Principal Research Scientist Emre Gençer, helped the team transport more than 150 used vehicles — Nissan Pathfinders and vans for moving civilians away from the front, Ford pickups for transporting anti-missile defense systems — and hundreds of batteries, generators, drones, bulletproof vests, and helmets to the front through nightmarish logistical bottlenecks.

      Typically, supplies from the United States, Asia, and elsewhere in Europe move through Gdansk and Warsaw, then proceed via train or vehicle to warehouses in Lviv, around 70 kilometers east of the border. Next is the seven-hour trip to Kyiv or the 12-hour drive to Dnipro (the current southern edge of the safe “green zone”) and the final 200 kilometers to the front. Here, says Miller, drivers with training and protective gear, often members of the Ukrainian military, take vehicles and supplies to front-line end users.

      “From day one, we asked our Ukrainian members and partners for introductions, and we’re constantly looking for more,” Miller says. “When our vehicles reach the front lines, Evan’s team always does interviews about needs, and what’s working, what’s not. What’s saving the most lives.”

      “From my early days with Ian, it’s clear he was always looking for ways to help people. Connections were really important to him,” says MITEI Director Robert C. Armstrong. “When war broke out, he found the call to answer human need irresistible. I think many of us think of doing that, but we get bogged down in the mechanics of everyday life. He just picked up and went.

      “Ian is just a terrific person and a great role model,” Armstrong says.

      Accelerating peace

      From the time Miller arrived in late February through October 2022, he continued working remotely for MITEI. He now works full time as co-director of Zero Line. For the foreseeable future, Miller will remain in Ukraine and Poland.

      He wants to see Ukrainians “follow in the happy, free, prospering footsteps of other ex-Soviet states, like the Baltics,” he says. He’d like to see the supply-chain innovations he and Platt achieved applied to humanitarian crises elsewhere.

      To date, Zero Line has raised more than $5 million in donations and delivered hundreds of tons of high-impact aid. “A key part of our approach has always been to support Ukrainians who excel in saving lives,” Miller says. To that end, the group works with Ukrainian software programmers and military units to create digital maps and processes to replace paper maps and operations “reminiscent of World War II,” Platt says. “Modernizing the intelligence infrastructure to facilitate better military operations is an important part of how a smaller military can beat a larger, more powerful military.”

      The fact that energy underlies so many aspects of the war is never far from Miller’s mind. Russia cut off energy supplies to Europe, then targeted Ukraine’s energy infrastructure. On one hand, he understands that billions of people in developing countries such as India need and deserve affordable energy. On the other hand, he says, oil and gas purchases by those countries are directly funding Russia’s war machine.

      “Everyone wants cheap renewables and we’re getting there, but it’s taking time. Lowering the costs of renewables and energy storage and supporting nascent commercial fusion — that’s a very important focus of MITEI. In the long run, that’ll help us reach a more peaceful world, without a doubt.”

      Work at MITEI and at Zero Line, Miller says, “truly could accelerate peace.” More

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      in Environment

      Engineering for social impact

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      A desire to make meaningful contributions to society has influenced Runako Gentles’ path in life. Gentles grew up in Jamaica with a supportive extended family that instilled in him his connection to his faith and his aspiration to aim for greatness.

      “While growing up, I was encouraged to live a life that could potentially bring about major positive changes in my family and many other people’s lives,” says the MIT junior.

      One of those pathways his parents encouraged is pursuing excellence in academics.

      Gentles attended Campion College, a Jesuit high school in Jamaica for academically high-achieving students. Gentles was valedictorian and even won an award “for the member of the valedictory class who most closely resembles the ideal of intellectual competence, openness to growth, and commitment to social justice.”

      Although he did well in all subjects, he naturally gravitated toward biology and chemistry. “There are certain subjects people just make sense of material much faster, and high school biology and chemistry were those subjects for me,” he says. His love of learning often surprised friends and classmates when he could recall science concepts and definitions years later.  

      For several years Gentles wanted to pursue the field of medicine. He remembers becoming more excited about the career of a surgeon after reading a book on the story of retired neurosurgeon Ben Carson. During his advanced studies at Campion, he attended a career event and met with a neurosurgeon who invited him and other classmates to watch a surgical procedure. Gentles had the unique learning experience to observe a spinal operation. Around that same time another learning opportunity presented itself. His biology teacher recommended he apply to a Caribbean Science Foundation initiative called Student Program for Innovation, Science, and Engineering (SPISE) to explore careers in science, technology, engineering, and math. The intensive residential summer program for Caribbean students is modeled after the Minority Introduction to Engineering and Science (MITES) program at MIT. Cardinal Warde, a professor of electrical engineering at MIT who is also from the Caribbean, serves as the faculty director for both MITES and SPISE. The program was Gentles’ first major exposure to engineering.

      “I felt like I was in my first year of college at SPISE. It was an amazing experience and it helped me realize the opportunities that an engineering career path offers,” Gentles says. He excelled in the SPISE program, even winning one of the program’s highest honors for demonstrating overall excellence and leadership.

      SPISE was profoundly impactful to Gentles and he decided to pursue engineering at MIT. While further exploring his engineering interests before his first year at MIT, he remembers reading an article that piqued his interest in industry sectors that met basic human and societal needs.

      “I started thinking more about engineering and ethics,” says Gentles. He wanted to spend his time learning how to use science and engineering to make meaningful change in society.  “I think back to wanting to be a doctor for many years to help sick people, but I took it a step further. I wanted to get closer to addressing some of the root causes of deaths, illnesses, and the poor quality of life for billions of people,” he says of his decision to pursue a degree in civil and environmental engineering.

      Gentles spent his first semester at MIT working as a remote student when the Covid pandemic shut down in-person learning. He participated in 1.097 (Introduction to Civil and Environmental Engineering Research) during the January Independent Activities Period, in which undergraduates work one-on-one with graduate students or postdoc mentors on research projects that align with their interests. Gentles worked in the lab of Ruben Juanes exploring the use of machine learning to analyze earthquake data to determine whether different geologic faults in Puerto Rico resulted in distinguishable earthquake clusters. He joined the lab of Desiree Plata in the summer of his sophomore year on another undergraduate research opportunity (UROP) project, analyzing diesel range organic compounds in water samples collected from shallow groundwater sources near hydraulic fracking sites in West Virginia. The experience even led Gentles to be a co-author in his graduate student mentor’s abstract proposal for the American Geophysical Union Fall Meeting 2022 conference.  

      Gentles says he found the Department of Civil and Environmental Engineering a place for him to have the big-picture mindset of thinking about how technology is going to affect the environment, which ultimately affects society. “Choosing this department was not just about gaining the technical knowledge that most interested me. I wanted to be in a space where I would significantly develop my mindset of using innovation to bring more harmony between society and the environment,” says Gentles.

      Outside of the classroom, learning acoustic guitar is a passion for Gentles. He plays at social events for Cru, a Christian community at MIT, where he serves as a team leader. He credits Cru with helping him feel connected to a lot of different people, even outside of MIT.

      He’s also a member of the Bernard M. Gordon-MIT Engineering Leadership Program, which helps undergraduates gain and hone leadership skills to prepare them for careers in engineering. After learning and exploring more UROPs and classes in civil and environmental engineering, he aspires to hold a position of leadership where he can use his environmental knowledge to impact human lives.

      “Mitigating environmental issues can sometimes be a very complicated endeavor involving many stakeholders,” Gentles says. “We need more bright minds to be thinking of creative ways to address these pressing problems. We need more leaders helping to make society more harmonious with our planet.” More

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      in Energy

      Flow batteries for grid-scale energy storage

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      In the coming decades, renewable energy sources such as solar and wind will increasingly dominate the conventional power grid. Because those sources only generate electricity when it’s sunny or windy, ensuring a reliable grid — one that can deliver power 24/7 — requires some means of storing electricity when supplies are abundant and delivering it later when they’re not. And because there can be hours and even days with no wind, for example, some energy storage devices must be able to store a large amount of electricity for a long time.

      A promising technology for performing that task is the flow battery, an electrochemical device that can store hundreds of megawatt-hours of energy — enough to keep thousands of homes running for many hours on a single charge. Flow batteries have the potential for long lifetimes and low costs in part due to their unusual design. In the everyday batteries used in phones and electric vehicles, the materials that store the electric charge are solid coatings on the electrodes. “A flow battery takes those solid-state charge-storage materials, dissolves them in electrolyte solutions, and then pumps the solutions through the electrodes,” says Fikile Brushett, an associate professor of chemical engineering at MIT. That design offers many benefits and poses a few challenges.

      Flow batteries: Design and operation

      A flow battery contains two substances that undergo electrochemical reactions in which electrons are transferred from one to the other. When the battery is being charged, the transfer of electrons forces the two substances into a state that’s “less energetically favorable” as it stores extra energy. (Think of a ball being pushed up to the top of a hill.) When the battery is being discharged, the transfer of electrons shifts the substances into a more energetically favorable state as the stored energy is released. (The ball is set free and allowed to roll down the hill.)

      At the core of a flow battery are two large tanks that hold liquid electrolytes, one positive and the other negative. Each electrolyte contains dissolved “active species” — atoms or molecules that will electrochemically react to release or store electrons. During charging, one species is “oxidized” (releases electrons), and the other is “reduced” (gains electrons); during discharging, they swap roles. Pumps are used to circulate the two electrolytes through separate electrodes, each made of a porous material that provides abundant surfaces on which the active species can react. A thin membrane between the adjacent electrodes keeps the two electrolytes from coming into direct contact and possibly reacting, which would release heat and waste energy that could otherwise be used on the grid.

      When the battery is being discharged, active species on the negative side oxidize, releasing electrons that flow through an external circuit to the positive side, causing the species there to be reduced. The flow of those electrons through the external circuit can power the grid. In addition to the movement of the electrons, “supporting” ions — other charged species in the electrolyte — pass through the membrane to help complete the reaction and keep the system electrically neutral.

      Once all the species have reacted and the battery is fully discharged, the system can be recharged. In that process, electricity from wind turbines, solar farms, and other generating sources drives the reverse reactions. The active species on the positive side oxidize to release electrons back through the wires to the negative side, where they rejoin their original active species. The battery is now reset and ready to send out more electricity when it’s needed. Brushett adds, “The battery can be cycled in this way over and over again for years on end.”

      Benefits and challenges

      A major advantage of this system design is that where the energy is stored (the tanks) is separated from where the electrochemical reactions occur (the so-called reactor, which includes the porous electrodes and membrane). As a result, the capacity of the battery — how much energy it can store — and its power — the rate at which it can be charged and discharged — can be adjusted separately. “If I want to have more capacity, I can just make the tanks bigger,” explains Kara Rodby PhD ’22, a former member of Brushett’s lab and now a technical analyst at Volta Energy Technologies. “And if I want to increase its power, I can increase the size of the reactor.” That flexibility makes it possible to design a flow battery to suit a particular application and to modify it if needs change in the future.

      However, the electrolyte in a flow battery can degrade with time and use. While all batteries experience electrolyte degradation, flow batteries in particular suffer from a relatively faster form of degradation called “crossover.” The membrane is designed to allow small supporting ions to pass through and block the larger active species, but in reality, it isn’t perfectly selective. Some of the active species in one tank can sneak through (or “cross over”) and mix with the electrolyte in the other tank. The two active species may then chemically react, effectively discharging the battery. Even if they don’t, some of the active species is no longer in the first tank where it belongs, so the overall capacity of the battery is lower.

      Recovering capacity lost to crossover requires some sort of remediation — for example, replacing the electrolyte in one or both tanks or finding a way to reestablish the “oxidation states” of the active species in the two tanks. (Oxidation state is a number assigned to an atom or compound to tell if it has more or fewer electrons than it has when it’s in its neutral state.) Such remediation is more easily — and therefore more cost-effectively — executed in a flow battery because all the components are more easily accessed than they are in a conventional battery.

      The state of the art: Vanadium

      A critical factor in designing flow batteries is the selected chemistry. The two electrolytes can contain different chemicals, but today the most widely used setup has vanadium in different oxidation states on the two sides. That arrangement addresses the two major challenges with flow batteries.

      First, vanadium doesn’t degrade. “If you put 100 grams of vanadium into your battery and you come back in 100 years, you should be able to recover 100 grams of that vanadium — as long as the battery doesn’t have some sort of a physical leak,” says Brushett.

      And second, if some of the vanadium in one tank flows through the membrane to the other side, there is no permanent cross-contamination of the electrolytes, only a shift in the oxidation states, which is easily remediated by re-balancing the electrolyte volumes and restoring the oxidation state via a minor charge step. Most of today’s commercial systems include a pipe connecting the two vanadium tanks that automatically transfers a certain amount of electrolyte from one tank to the other when the two get out of balance.

      However, as the grid becomes increasingly dominated by renewables, more and more flow batteries will be needed to provide long-duration storage. Demand for vanadium will grow, and that will be a problem. “Vanadium is found around the world but in dilute amounts, and extracting it is difficult,” says Rodby. “So there are limited places — mostly in Russia, China, and South Africa — where it’s produced, and the supply chain isn’t reliable.” As a result, vanadium prices are both high and extremely volatile — an impediment to the broad deployment of the vanadium flow battery.

      Beyond vanadium

      The question then becomes: If not vanadium, then what? Researchers worldwide are trying to answer that question, and many are focusing on promising chemistries using materials that are more abundant and less expensive than vanadium. But it’s not that easy, notes Rodby. While other chemistries may offer lower initial capital costs, they may be more expensive to operate over time. They may require periodic servicing to rejuvenate one or both of their electrolytes. “You may even need to replace them, so you’re essentially incurring that initial (low) capital cost again and again,” says Rodby.

      Indeed, comparing the economics of different options is difficult because “there are so many dependent variables,” says Brushett. “A flow battery is an electrochemical system, which means that there are multiple components working together in order for the device to function. Because of that, if you are trying to improve a system — performance, cost, whatever — it’s very difficult because when you touch one thing, five other things change.”

      So how can we compare these new and emerging chemistries — in a meaningful way — with today’s vanadium systems? And how do we compare them with one another, so we know which ones are more promising and what the potential pitfalls are with each one? “Addressing those questions can help us decide where to focus our research and where to invest our research and development dollars now,” says Brushett.

      Techno-economic modeling as a guide

      A good way to understand and assess the economic viability of new and emerging energy technologies is using techno-economic modeling. With certain models, one can account for the capital cost of a defined system and — based on the system’s projected performance — the operating costs over time, generating a total cost discounted over the system’s lifetime. That result allows a potential purchaser to compare options on a “levelized cost of storage” basis.

      Using that approach, Rodby developed a framework for estimating the levelized cost for flow batteries. The framework includes a dynamic physical model of the battery that tracks its performance over time, including any changes in storage capacity. The calculated operating costs therefore cover all services required over decades of operation, including the remediation steps taken in response to species degradation and crossover.

      Analyzing all possible chemistries would be impossible, so the researchers focused on certain classes. First, they narrowed the options down to those in which the active species are dissolved in water. “Aqueous systems are furthest along and are most likely to be successful commercially,” says Rodby. Next, they limited their analyses to “asymmetric” chemistries; that is, setups that use different materials in the two tanks. (As Brushett explains, vanadium is unusual in that using the same “parent” material in both tanks is rarely feasible.) Finally, they divided the possibilities into two classes: species that have a finite lifetime and species that have an infinite lifetime; that is, ones that degrade over time and ones that don’t.

      Results from their analyses aren’t clear-cut; there isn’t a particular chemistry that leads the pack. But they do provide general guidelines for choosing and pursuing the different options.

      Finite-lifetime materials

      While vanadium is a single element, the finite-lifetime materials are typically organic molecules made up of multiple elements, among them carbon. One advantage of organic molecules is that they can be synthesized in a lab and at an industrial scale, and the structure can be altered to suit a specific function. For example, the molecule can be made more soluble, so more will be present in the electrolyte and the energy density of the system will be greater; or it can be made bigger so it won’t fit through the membrane and cross to the other side. Finally, organic molecules can be made from simple, abundant, low-cost elements, potentially even waste streams from other industries.

      Despite those attractive features, there are two concerns. First, organic molecules would probably need to be made in a chemical plant, and upgrading the low-cost precursors as needed may prove to be more expensive than desired. Second, these molecules are large chemical structures that aren’t always very stable, so they’re prone to degradation. “So along with crossover, you now have a new degradation mechanism that occurs over time,” says Rodby. “Moreover, you may figure out the degradation process and how to reverse it in one type of organic molecule, but the process may be totally different in the next molecule you work on, making the discovery and development of each new chemistry require significant effort.”

      Research is ongoing, but at present, Rodby and Brushett find it challenging to make the case for the finite-lifetime chemistries, mostly based on their capital costs. Citing studies that have estimated the manufacturing costs of these materials, Rodby believes that current options cannot be made at low enough costs to be economically viable. “They’re cheaper than vanadium, but not cheap enough,” says Rodby.

      The results send an important message to researchers designing new chemistries using organic molecules: Be sure to consider operating challenges early on. Rodby and Brushett note that it’s often not until way down the “innovation pipeline” that researchers start to address practical questions concerning the long-term operation of a promising-looking system. The MIT team recommends that understanding the potential decay mechanisms and how they might be cost-effectively reversed or remediated should be an upfront design criterion.

      Infinite-lifetime species

      The infinite-lifetime species include materials that — like vanadium — are not going to decay. The most likely candidates are other metals; for example, iron or manganese. “These are commodity-scale chemicals that will certainly be low cost,” says Rodby.

      Here, the researchers found that there’s a wider “design space” of feasible options that could compete with vanadium. But there are still challenges to be addressed. While these species don’t degrade, they may trigger side reactions when used in a battery. For example, many metals catalyze the formation of hydrogen, which reduces efficiency and adds another form of capacity loss. While there are ways to deal with the hydrogen-evolution problem, a sufficiently low-cost and effective solution for high rates of this side reaction is still needed.

      In addition, crossover is a still a problem requiring remediation steps. The researchers evaluated two methods of dealing with crossover in systems combining two types of infinite-lifetime species.

      The first is the “spectator strategy.” Here, both of the tanks contain both active species. Explains Brushett, “You have the same electrolyte mixture on both sides of the battery, but only one of the species is ever working and the other is a spectator.” As a result, crossover can be remediated in similar ways to those used in the vanadium flow battery. The drawback is that half of the active material in each tank is unavailable for storing charge, so it’s wasted. “You’ve essentially doubled your electrolyte cost on a per-unit energy basis,” says Rodby.

      The second method calls for making a membrane that is perfectly selective: It must let through only the supporting ion needed to maintain the electrical balance between the two sides. However, that approach increases cell resistance, hurting system efficiency. In addition, the membrane would need to be made of a special material — say, a ceramic composite — that would be extremely expensive based on current production methods and scales. Rodby notes that work on such membranes is under way, but the cost and performance metrics are “far off from where they’d need to be to make sense.”

      Time is of the essence

      The researchers stress the urgency of the climate change threat and the need to have grid-scale, long-duration storage systems at the ready. “There are many chemistries now being looked at,” says Rodby, “but we need to hone in on some solutions that will actually be able to compete with vanadium and can be deployed soon and operated over the long term.”

      The techno-economic framework is intended to help guide that process. It can calculate the levelized cost of storage for specific designs for comparison with vanadium systems and with one another. It can identify critical gaps in knowledge related to long-term operation or remediation, thereby identifying technology development or experimental investigations that should be prioritized. And it can help determine whether the trade-off between lower upfront costs and greater operating costs makes sense in these next-generation chemistries.

      The good news, notes Rodby, is that advances achieved in research on one type of flow battery chemistry can often be applied to others. “A lot of the principles learned with vanadium can be translated to other systems,” she says. She believes that the field has advanced not only in understanding but also in the ability to design experiments that address problems common to all flow batteries, thereby helping to prepare the technology for its important role of grid-scale storage in the future.

      This research was supported by the MIT Energy Initiative. Kara Rodby PhD ’22 was supported by an ExxonMobil-MIT Energy Fellowship in 2021-22.

      This article appears in the Winter 2023 issue of Energy Futures, the magazine of the MIT Energy Initiative. More

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      in Energy

      An interdisciplinary approach to fighting climate change through clean energy solutions

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      In early 2021, the U.S. government set an ambitious goal: to decarbonize its power grid, the system that generates and transmits electricity throughout the country, by 2035. It’s an important goal in the fight against climate change, and will require a switch from current, greenhouse-gas producing energy sources (such as coal and natural gas), to predominantly renewable ones (such as wind and solar).

      Getting the power grid to zero carbon will be a challenging undertaking, as Audun Botterud, a principal research scientist at the MIT Laboratory for Information and Decision Systems (LIDS) who has long been interested in the problem, knows well. It will require building lots of renewable energy generators and new infrastructure; designing better technology to capture, store, and carry electricity; creating the right regulatory and economic incentives; and more. Decarbonizing the grid also presents many computational challenges, which is where Botterud’s focus lies. Botterud has modeled different aspects of the grid — the mechanics of energy supply, demand, and storage, and electricity markets — where economic factors can have a huge effect on how quickly renewable solutions get adopted.

      On again, off again

      A major challenge of decarbonization is that the grid must be designed and operated to reliably meet demand. Using renewable energy sources complicates this, as wind and solar power depend on an infamously volatile system: the weather. A sunny day becomes gray and blustery, and wind turbines get a boost but solar farms go idle. This will make the grid’s energy supply variable and hard to predict. Additional resources, including batteries and backup power generators, will need to be incorporated to regulate supply. Extreme weather events, which are becoming more common with climate change, can further strain both supply and demand. Managing a renewables-driven grid will require algorithms that can minimize uncertainty in the face of constant, sometimes random fluctuations to make better predictions of supply and demand, guide how resources are added to the grid, and inform how those resources are committed and dispatched across the entire United States.

      “The problem of managing supply and demand in the grid has to happen every second throughout the year, and given how much we rely on electricity in society, we need to get this right,” Botterud says. “You cannot let the reliability drop as you increase the amount of renewables, especially because I think that will lead to resistance towards adopting renewables.”

      That is why Botterud feels fortunate to be working on the decarbonization problem at LIDS — even though a career here is not something he had originally planned. Botterud’s first experience with MIT came during his time as a graduate student in his home country of Norway, when he spent a year as a visiting student with what is now called the MIT Energy Initiative. He might never have returned, except that while at MIT, Botterud met his future wife, Bilge Yildiz. The pair both ended up working at the Argonne National Laboratory outside of Chicago, with Botterud focusing on challenges related to power systems and electricity markets. Then Yildiz got a faculty position at MIT, where she is a professor of nuclear and materials science and engineering. Botterud moved back to the Cambridge area with her and continued to work for Argonne remotely, but he also kept an eye on local opportunities. Eventually, a position at LIDS became available, and Botterud took it, while maintaining his connections to Argonne.

      “At first glance, it may not be an obvious fit,” Botterud says. “My work is very focused on a specific application, power system challenges, and LIDS tends to be more focused on fundamental methods to use across many different application areas. However, being at LIDS, my lab [the Energy Analytics Group] has access to the most recent advances in these fundamental methods, and we can apply them to power and energy problems. Other people at LIDS are working on energy too, so there is growing momentum to address these important problems.”

      Weather, space, and time

      Much of Botterud’s research involves optimization, using mathematical programming to compare alternatives and find the best solution. Common computational challenges include dealing with large geographical areas that contain regions with different weather, different types and quantities of renewable energy available, and different infrastructure and consumer needs — such as the entire United States. Another challenge is the need for granular time resolution, sometimes even down to the sub-second level, to account for changes in energy supply and demand.

      Often, Botterud’s group will use decomposition to solve such large problems piecemeal and then stitch together solutions. However, it’s also important to consider systems as a whole. For example, in a recent paper, Botterud’s lab looked at the effect of building new transmission lines as part of national decarbonization. They modeled solutions assuming coordination at the state, regional, or national level, and found that the more regions coordinate to build transmission infrastructure and distribute electricity, the less they will need to spend to reach zero carbon.

      In other projects, Botterud uses game theory approaches to study strategic interactions in electricity markets. For example, he has designed agent-based models to analyze electricity markets. These assume each actor will make strategic decisions in their own best interest and then simulate interactions between them. Interested parties can use the models to see what would happen under different conditions and market rules, which may lead companies to make different investment decisions, or governing bodies to issue different regulations and incentives. These choices can shape how quickly the grid gets decarbonized.

      Botterud is also collaborating with researchers in MIT’s chemical engineering department who are working on improving battery storage technologies. Batteries will help manage variable renewable energy supply by capturing surplus energy during periods of high generation to release during periods of insufficient generation. Botterud’s group models the sort of charge cycles that batteries are likely to experience in the power grid, so that chemical engineers in the lab can test their batteries’ abilities in more realistic scenarios. In turn, this also leads to a more realistic representation of batteries in power system optimization models.

      These are only some of the problems that Botterud works on. He enjoys the challenge of tackling a spectrum of different projects, collaborating with everyone from engineers to architects to economists. He also believes that such collaboration leads to better solutions. The problems created by climate change are myriad and complex, and solving them will require researchers to cooperate and explore.

      “In order to have a real impact on interdisciplinary problems like energy and climate,” Botterud says, “you need to get outside of your research sweet spot and broaden your approach.” More

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      in Environment

      3 Questions: Leveraging carbon uptake to lower concrete’s carbon footprint

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      To secure a more sustainable and resilient future, we must take a careful look at the life cycle impacts of humanity’s most-produced building material: concrete. Carbon uptake, the process by which cement-based products sequester carbon dioxide, is key to this understanding.

      Hessam AzariJafari, the MIT Concrete Sustainability Hub’s deputy director, is deeply invested in the study of this process and its acceleration, where prudent. Here, he describes how carbon uptake is a key lever to reach a carbon-neutral concrete industry.

      Q: What is carbon uptake in cement-based products and how can it influence their properties?

      A: Carbon uptake, or carbonation, is a natural process of permanently sequestering CO2 from the atmosphere by hardened cement-based products like concretes and mortars. Through this reaction, these products form different kinds of limes or calcium carbonates. This uptake occurs slowly but significantly during two phases of the life cycle of cement-based products: the use phase and the end-of-life phase.

      In general, carbon uptake increases the compressive strength of cement-based products as it can densify the paste. At the same time, carbon uptake can impact the corrosion resistance of concrete. In concrete that is reinforced with steel, the corrosion process can be initiated if the carbonation happens extensively (e.g., the whole of the concrete cover is carbonated) and intensively (e.g., a significant proportion of the hardened cement product is carbonated). [Concrete cover is the layer distance between the surface of reinforcement and the outer surface of the concrete.]

      Q: What are the factors that influence carbon uptake?

      A: The intensity of carbon uptake depends on four major factors: the climate, the types and properties of cement-based products used, the composition of binders (cement type) used, and the geometry and exposure condition of the structure.

      In regard to climate, the humidity and temperature affect the carbon uptake rate. In very low or very high humidity conditions, the carbon uptake process is slowed. High temperatures speed the process. The local atmosphere’s carbon dioxide concentration can affect the carbon uptake rate. For example, in urban areas, carbon uptake is an order of magnitude faster than in suburban areas.

      The types and properties of cement-based products have a large influence on the rate of carbon uptake. For example, mortar (consisting of water, cement, and fine aggregates) carbonates two to four times faster than concrete (consisting of water, cement, and coarse and fine aggregates) because of its more porous structure.The carbon uptake rate of dry-cast concrete masonry units is higher than wet-cast for the same reason. In structural concrete, the process is made slower as mechanical properties are improved and the density of the hardened products’ structure increases.

      Lastly, a structure’s surface area-to-volume ratio and exposure to air and water can have ramifications for its rate of carbonation. When cement-based products are covered, carbonation may be slowed or stopped. Concrete that is exposed to fresh air while being sheltered from rain can have a larger carbon uptake compared to cement-based products that are painted or carpeted. Additionally, cement-based elements with large surface areas, like thin concrete structures or mortar layers, allow uptake to progress more extensively.

      Q: What is the role of carbon uptake in the carbon neutrality of concrete, and how should architects and engineers account for it when designing for specific applications?

      A: Carbon uptake is a part of the life cycle of any cement-based products that should be accounted for in carbon footprint calculations. Our evaluation shows the U.S. pavement network can sequester 5.8 million metric tons of CO2, of which 52 percent will be sequestered when the demolished concrete is stockpiled at its end of life.

      From one concrete structure to another, the percentage of emissions sequestered may vary. For instance, concrete bridges tend to have a lower percentage versus buildings constructed with concrete masonry. In any case, carbon uptake can influence the life cycle environmental performance of concrete.

      At the MIT Concrete Sustainability Hub, we have developed a calculator to enable construction stakeholders to estimate the carbon uptake of concrete structures during their use and end-of-life phases.

      Looking toward the future, carbon uptake’s role in the carbon neutralization of cement-based products could grow in importance. While caution should be taken in regards to uptake when reinforcing steel is embedded in concrete, there are opportunities for different stakeholders to augment carbon uptake in different cement-based products.

      Architects can influence the shape of concrete elements to increase the surface area-to-volume ratio (e.g., making “waffle” patterns on slabs and walls, or having several thin towers instead of fewer large ones on an apartment complex). Concrete manufacturers can adjust the binder type and quantity while delivering concrete that meets performance requirements. Finally, industrial ecologists and life-cycle assessment practitioners need to work on the tools and add-ons to make sure the impact of carbon is well captured when assessing the potential impacts of cement-based products in buildings and infrastructure systems.

      Currently, the cement and concrete industry is working with tech companies as well as local, state, and federal governments to lower and subsidize the code of carbon capture sequestration and neutralization. Accelerating carbon uptake where reasonable could be an additional lever to neutralize the carbon emissions of the concrete value chain.

      Carbon uptake is one more piece of the puzzle that makes concrete a sustainable choice for building in many applications. The sustainability and resilience of the future built environment lean on the use of concrete. There is still much work to be done to truly build sustainably, and understanding carbon uptake is an important place to begin. More