Evelyn Reynolds

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    Designing better batteries for electric vehicles

    The urgent need to cut carbon emissions is prompting a rapid move toward electrified mobility and expanded deployment of solar and wind on the electric grid. If those trends escalate as expected, the need for better methods of storing electrical energy will intensify.

    “We need all the strategies we can get to address the threat of climate change,” says Elsa Olivetti PhD ’07, the Esther and Harold E. Edgerton Associate Professor in Materials Science and Engineering. “Obviously, developing technologies for grid-based storage at a large scale is critical. But for mobile applications — in particular, transportation — much research is focusing on adapting today’s lithium-ion battery to make versions that are safer, smaller, and can store more energy for their size and weight.”

    Traditional lithium-ion batteries continue to improve, but they have limitations that persist, in part because of their structure. A lithium-ion battery consists of two electrodes — one positive and one negative — sandwiched around an organic (carbon-containing) liquid. As the battery is charged and discharged, electrically charged particles (or ions) of lithium pass from one electrode to the other through the liquid electrolyte.

    One problem with that design is that at certain voltages and temperatures, the liquid electrolyte can become volatile and catch fire. “Batteries are generally safe under normal usage, but the risk is still there,” says Kevin Huang PhD ’15, a research scientist in Olivetti’s group.

    Another problem is that lithium-ion batteries are not well-suited for use in vehicles. Large, heavy battery packs take up space and increase a vehicle’s overall weight, reducing fuel efficiency. But it’s proving difficult to make today’s lithium-ion batteries smaller and lighter while maintaining their energy density — that is, the amount of energy they store per gram of weight.

    To solve those problems, researchers are changing key features of the lithium-ion battery to make an all-solid, or “solid-state,” version. They replace the liquid electrolyte in the middle with a thin, solid electrolyte that’s stable at a wide range of voltages and temperatures. With that solid electrolyte, they use a high-capacity positive electrode and a high-capacity, lithium metal negative electrode that’s far thinner than the usual layer of porous carbon. Those changes make it possible to shrink the overall battery considerably while maintaining its energy-storage capacity, thereby achieving a higher energy density.

    “Those features — enhanced safety and greater energy density — are probably the two most-often-touted advantages of a potential solid-state battery,” says Huang. He then quickly clarifies that “all of these things are prospective, hoped-for, and not necessarily realized.” Nevertheless, the possibility has many researchers scrambling to find materials and designs that can deliver on that promise.

    Thinking beyond the lab

    Researchers have come up with many intriguing options that look promising — in the lab. But Olivetti and Huang believe that additional practical considerations may be important, given the urgency of the climate change challenge. “There are always metrics that we researchers use in the lab to evaluate possible materials and processes,” says Olivetti. Examples might include energy-storage capacity and charge/discharge rate. When performing basic research — which she deems both necessary and important — those metrics are appropriate. “But if the aim is implementation, we suggest adding a few metrics that specifically address the potential for rapid scaling,” she says.

    Based on industry’s experience with current lithium-ion batteries, the MIT researchers and their colleague Gerbrand Ceder, the Daniel M. Tellep Distinguished Professor of Engineering at the University of California at Berkeley, suggest three broad questions that can help identify potential constraints on future scale-up as a result of materials selection. First, with this battery design, could materials availability, supply chains, or price volatility become a problem as production scales up? (Note that the environmental and other concerns raised by expanded mining are outside the scope of this study.) Second, will fabricating batteries from these materials involve difficult manufacturing steps during which parts are likely to fail? And third, do manufacturing measures needed to ensure a high-performance product based on these materials ultimately lower or raise the cost of the batteries produced?

    To demonstrate their approach, Olivetti, Ceder, and Huang examined some of the electrolyte chemistries and battery structures now being investigated by researchers. To select their examples, they turned to previous work in which they and their collaborators used text- and data-mining techniques to gather information on materials and processing details reported in the literature. From that database, they selected a few frequently reported options that represent a range of possibilities.

    Materials and availability

    In the world of solid inorganic electrolytes, there are two main classes of materials — the oxides, which contain oxygen, and the sulfides, which contain sulfur. Olivetti, Ceder, and Huang focused on one promising electrolyte option in each class and examined key elements of concern for each of them.

    The sulfide they considered was LGPS, which combines lithium, germanium, phosphorus, and sulfur. Based on availability considerations, they focused on the germanium, an element that raises concerns in part because it’s not generally mined on its own. Instead, it’s a byproduct produced during the mining of coal and zinc.

    To investigate its availability, the researchers looked at how much germanium was produced annually in the past six decades during coal and zinc mining and then at how much could have been produced. The outcome suggested that 100 times more germanium could have been produced, even in recent years. Given that supply potential, the availability of germanium is not likely to constrain the scale-up of a solid-state battery based on an LGPS electrolyte.

    The situation looked less promising with the researchers’ selected oxide, LLZO, which consists of lithium, lanthanum, zirconium, and oxygen. Extraction and processing of lanthanum are largely concentrated in China, and there’s limited data available, so the researchers didn’t try to analyze its availability. The other three elements are abundantly available. However, in practice, a small quantity of another element — called a dopant — must be added to make LLZO easy to process. So the team focused on tantalum, the most frequently used dopant, as the main element of concern for LLZO.

    Tantalum is produced as a byproduct of tin and niobium mining. Historical data show that the amount of tantalum produced during tin and niobium mining was much closer to the potential maximum than was the case with germanium. So the availability of tantalum is more of a concern for the possible scale-up of an LLZO-based battery.

    But knowing the availability of an element in the ground doesn’t address the steps required to get it to a manufacturer. So the researchers investigated a follow-on question concerning the supply chains for critical elements — mining, processing, refining, shipping, and so on. Assuming that abundant supplies are available, can the supply chains that deliver those materials expand quickly enough to meet the growing demand for batteries?

    In sample analyses, they looked at how much supply chains for germanium and tantalum would need to grow year to year to provide batteries for a projected fleet of electric vehicles in 2030. As an example, an electric vehicle fleet often cited as a goal for 2030 would require production of enough batteries to deliver a total of 100 gigawatt hours of energy. To meet that goal using just LGPS batteries, the supply chain for germanium would need to grow by 50 percent from year to year — a stretch, since the maximum growth rate in the past has been about 7 percent. Using just LLZO batteries, the supply chain for tantalum would need to grow by about 30 percent — a growth rate well above the historical high of about 10 percent.

    Those examples demonstrate the importance of considering both materials availability and supply chains when evaluating different solid electrolytes for their scale-up potential. “Even when the quantity of a material available isn’t a concern, as is the case with germanium, scaling all the steps in the supply chain to match the future production of electric vehicles may require a growth rate that’s literally unprecedented,” says Huang.

    Materials and processing

    In assessing the potential for scale-up of a battery design, another factor to consider is the difficulty of the manufacturing process and how it may impact cost. Fabricating a solid-state battery inevitably involves many steps, and a failure at any step raises the cost of each battery successfully produced. As Huang explains, “You’re not shipping those failed batteries; you’re throwing them away. But you’ve still spent money on the materials and time and processing.”

    As a proxy for manufacturing difficulty, Olivetti, Ceder, and Huang explored the impact of failure rate on overall cost for selected solid-state battery designs in their database. In one example, they focused on the oxide LLZO. LLZO is extremely brittle, and at the high temperatures involved in manufacturing, a large sheet that’s thin enough to use in a high-performance solid-state battery is likely to crack or warp.

    To determine the impact of such failures on cost, they modeled four key processing steps in assembling LLZO-based batteries. At each step, they calculated cost based on an assumed yield — that is, the fraction of total units that were successfully processed without failing. With the LLZO, the yield was far lower than with the other designs they examined; and, as the yield went down, the cost of each kilowatt-hour (kWh) of battery energy went up significantly. For example, when 5 percent more units failed during the final cathode heating step, cost increased by about $30/kWh — a nontrivial change considering that a commonly accepted target cost for such batteries is $100/kWh. Clearly, manufacturing difficulties can have a profound impact on the viability of a design for large-scale adoption.

    Materials and performance

    One of the main challenges in designing an all-solid battery comes from “interfaces” — that is, where one component meets another. During manufacturing or operation, materials at those interfaces can become unstable. “Atoms start going places that they shouldn’t, and battery performance declines,” says Huang.

    As a result, much research is devoted to coming up with methods of stabilizing interfaces in different battery designs. Many of the methods proposed do increase performance; and as a result, the cost of the battery in dollars per kWh goes down. But implementing such solutions generally involves added materials and time, increasing the cost per kWh during large-scale manufacturing.

    To illustrate that trade-off, the researchers first examined their oxide, LLZO. Here, the goal is to stabilize the interface between the LLZO electrolyte and the negative electrode by inserting a thin layer of tin between the two. They analyzed the impacts — both positive and negative — on cost of implementing that solution. They found that adding the tin separator increases energy-storage capacity and improves performance, which reduces the unit cost in dollars/kWh. But the cost of including the tin layer exceeds the savings so that the final cost is higher than the original cost.

    In another analysis, they looked at a sulfide electrolyte called LPSCl, which consists of lithium, phosphorus, and sulfur with a bit of added chlorine. In this case, the positive electrode incorporates particles of the electrolyte material — a method of ensuring that the lithium ions can find a pathway through the electrolyte to the other electrode. However, the added electrolyte particles are not compatible with other particles in the positive electrode — another interface problem. In this case, a standard solution is to add a “binder,” another material that makes the particles stick together.

    Their analysis confirmed that without the binder, performance is poor, and the cost of the LPSCl-based battery is more than $500/kWh. Adding the binder improves performance significantly, and the cost drops by almost $300/kWh. In this case, the cost of adding the binder during manufacturing is so low that essentially all the of the cost decrease from adding the binder is realized. Here, the method implemented to solve the interface problem pays off in lower costs.

    The researchers performed similar studies of other promising solid-state batteries reported in the literature, and their results were consistent: The choice of battery materials and processes can affect not only near-term outcomes in the lab but also the feasibility and cost of manufacturing the proposed solid-state battery at the scale needed to meet future demand. The results also showed that considering all three factors together — availability, processing needs, and battery performance — is important because there may be collective effects and trade-offs involved.

    Olivetti is proud of the range of concerns the team’s approach can probe. But she stresses that it’s not meant to replace traditional metrics used to guide materials and processing choices in the lab. “Instead, it’s meant to complement those metrics by also looking broadly at the sorts of things that could get in the way of scaling” — an important consideration given what Huang calls “the urgent ticking clock” of clean energy and climate change.

    This research was supported by the Seed Fund Program of the MIT Energy Initiative (MITEI) Low-Carbon Energy Center for Energy Storage; by Shell, a founding member of MITEI; and by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office, under the Advanced Battery Materials Research Program. The text mining work was supported by the National Science Foundation, the Office of Naval Research, and MITEI.

    This article appears in the Spring 2021 issue of Energy Futures, the magazine of the MIT Energy Initiative. More

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    Why boiling droplets can race across hot oily surfaces

    When you’re frying something in a skillet and some droplets of water fall into the pan, you may have noticed those droplets skittering around on top of the film of hot oil. Now, that seemingly trivial phenomenon has been analyzed and understood for the first time by researchers at MIT — and may have important implications for microfluidic devices, heat transfer systems, and other useful functions.

    A droplet of boiling water on a hot surface will sometimes levitate on a thin vapor film, a well-studied phenomenon called the Leidenfrost effect. Because it is suspended on a cushion of vapor, the droplet can move across the surface with little friction. If the surface is coated with hot oil, which has much greater friction than the vapor film under a Leidenfrost droplet, the hot droplet should be expected to move much more slowly. But, counterintuitively, the series of experiments at MIT has showed that the opposite effect happens: The droplet on oil zooms away much more rapidly than on bare metal.

    This effect, which propels droplets across a heated oily surface 10 to 100 times faster than on bare metal, could potentially be used for self-cleaning or de-icing systems, or to propel tiny amounts of liquid through the tiny tubing of microfluidic devices used for biomedical and chemical research and testing. The findings are described today in a paper in the journal Physical Review Letters, written by graduate student Victor Julio Leon and professor of mechanical engineering Kripa Varanasi.

    In previous research, Varanasi and his team showed that it would be possible to harness this phenomenon for some of these potential applications, but the new work, producing such high velocities (approximately 50 times faster), could open up even more new uses, Varanasi says.

    After long and painstaking analysis, Leon and Varanasi were able to determine the reason for the rapid ejection of these droplets from the hot surface. Under the right conditions of high temperature, oil viscosity, and oil thickness, the oil will form a kind of thin cloak coating the outside of each water droplet. As the droplet heats up, tiny bubbles of vapor form along the interface between the droplet and the oil. Because these minuscule bubbles accumulate randomly along the droplet’s base, asymmetries develop, and the lowered friction under the bubble loosens the droplet’s attachment to the surface and propels it away.

    The oily film acts almost like the rubber of a balloon, and when the tiny vapor bubbles burst through, they impart a force and “the balloon just flies off because the air is going out one side, creating a momentum transfer,” Varanasi says. Without the oil cloak, the vapor bubbles would just flow out of the droplet in all directions, preventing self-propulsion, but the cloaking effect holds them in like the skin of the balloon.

    Researchers used extreme high-speed photography to reveal the details of the moving droplets. “You can actually see the fluctuations on the surface,” graduate student Victor Leon says.

    The phenomenon sounds simple, but it turns out to depend on a complex interplay between events happening at different timescales.

    This newly analyzed self-ejection phenomenon depends on a number of factors, including the droplet size, the thickness and viscosity of the oil film, the thermal conductivity of the surface, the surface tension of the different liquids in the system, the type of oil, and the texture of the surface.

    In their experiments, the lowest viscosity of the several oils they tested was about 100 times more viscous than the surrounding air. So, it would have been expected to make bubbles move much more slowly than on the air cushion of the Leidenfrost effect. “That gives an idea of how surprising it is that this droplet is moving faster,” Leon says.

    As boiling starts, bubbles will randomly form from some nucleation site that is not right at its center. Bubble formation will increase on that side, leading to the propulsion off in one direction. So far, the researchers have not been able to control the direction of that randomly induced propulsion, but they are now working on some possible ways to control the directionality in the future. “We have ideas of how to trigger the propulsion in controlled directions,” Leon says.

    Remarkably, the tests showed that even though the oil film of the surface, which was a silicon wafer, was only 10 to 100 microns thick — about the thickness of a human hair — its behavior didn’t match the equations for a thin film. Instead, because of the vaporization the film, it was actually behaving like an infinitely deep pool of oil. “We were kind of astounded” by that finding, Leon says. While a thin film should have caused it to stick, the virtually infinite pool gave the droplet much lower friction, allowing it to move more rapidly than expected, Leon says.

    The effect depends on the fact that the formation of the tiny bubbles is a much more rapid process than the transfer of heat through the oil film, about a thousand times faster, leaving plenty of time for the asymmetries within the droplet to accumulate. When the bubbles of vapor initially form at the oil-water interface, they are  much more insulating that the liquid of the droplet, leading to significant thermal disturbances in the oil film. These disturbances cause the droplet to vibrate, reducing friction and increasing vaporization rate.

    It took extreme high-speed photography to reveal the details of this rapid effect, Leon says, using a 100,000 frames per second video camera. “You can actually see the fluctuations on the surface,” Leon says.

    Initially, Varanasi says, “we were stumped at multiple levels as to what was going on, because the effect was so unexpected. … It’s a fairly complex answer to what may look seemingly simple, but it really creates this fast propulsion.”

    In practice, the effect means that in certain situations, a simple heating of a surface, by the right amount and with the right kind of oily coating, could cause corrosive scaling drops to be cleared from a surface. Further down the line, once the researchers have more control over directionality, the system could potentially substitute for some high-tech pumps in microfluidic devices to propel droplets through the right tubes at the right time. This might be especially useful in microgravity situations, where ordinary pumps don’t function as usual.

    It may also be possible to attach a payload to the droplets, creating a kind of microscale robotic delivery system, Varanasi says. And while their tests focused on water droplets, potentially it could apply to many different kinds of liquids and sublimating solids, he says.

    The work was supported by the National Science Foundation. More

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    MIT Solar Electric Vehicle Team wins 2021 American Solar Challenge

    After three years of hard work, the MIT Solar Electric Vehicle Team took first place at the 2021 American Solar Challenge (ASC) on August 7 in the Single Occupancy Vehicle (SOV) category. During the five-day race, their solar car, Nimbus — designed and built entirely by students — beat eight other SOVs from schools across the country, traversing 1,109 miles and maintaining an average speed of 38.4 miles per hour.

    Held every two years, the ASC has traditionally been a timed event. This year, however, the race was based on the total distance traveled. Each team followed the same prescribed route, from Independence, Missouri, to Las Vegas, New Mexico. But teams could drive additional miles within each of the three stages — if their battery had enough juice to continue. Nimbus surpassed the closest runner-up, the University of Kentucky, by over 100 miles.

    “It’s still a little surreal,” says SEVT captain Aditya Mehrotra, a rising senior in electrical engineering and computer science. “We were all hopeful, but I don’t think you ever go into racing like, ‘We got this.’ It’s more like, ‘We’re going to do our best and see how we fare.’ In this case, we were fortunate enough to do really well. The car worked beautifully, and — more importantly — the team worked beautifully and we learned a lot.”

    Team work makes the dream work

    Two weeks before the ASC race, each solar car was put through its paces in the Formula Sun Grand Prix at Heartland Motorsports Park in Topeka, Kansas. First, vehicles had to perform a series of qualifying challenges, called “scrutineering.” Cars that passed could participate in a track race in hopes of qualifying for ASC. Nimbus placed second, completing a total of 239 laps around the track over three days (equivalent to 597.5 miles).

    In the process, SEVT member and rising junior in mechanical engineering Cameron Kokesh tied the Illinois State driver for the fastest single lap time around the track, clocking in at three minutes and 19 seconds. She’s not one to rest on her laurels, though. “It would be fun to see if we could beat that time at the next race,” she says with a smile.

    Nimbus’s performance at the Formula Sun Grand Prix and ASC is a manifestation of team’s proficiency in not only designing and building a superior solar vehicle, but other skills, as well, including managing logistics, communications, and teamwork. “It’s a huge operation,” says Mehrotra. “It’s not like we drive the car straight down the highway during the race.”

    Indeed, Nimbus travels with an impressive caravan of seven vehicles manned by about two dozen SEVT members. A scout vehicle is at the front, monitoring road and weather conditions, followed by a lead car that oversees navigation. Nimbus is third in the caravan, trailed by a chase vehicle, in which the strategy team manages tasks like monitoring telemetry data, calculating how much power the solar panels are generating and the remaining travel distance, and setting target speeds. Bringing up the rear are the transport truck and trailer, a media car, and “Cupcake,” a support vehicle with food, supplies, and camping gear.

    Leading up to the three-week event, the team devoted three years to designing, building, refining, and testing Nimbus. (The ASC was scheduled for 2020, but it was postponed until this year due to the Covid-19 pandemic.) They spent countless hours in the MIT Edgerton Center’s machine shop in Building N51, making, building, and iterating. They drove the car in the greater-Boston area, up to Salem, Massachusetts, and to Cape Cod. In the spring, they traveled to Palmer Motorsports Park in Palmer, Massachusetts, to practice various components of the race. They performed scrutineering tasks like the slalom test and figure eight test, conducted team operations training to optimize the caravan’s performance, and, of course, the “shakedown.” 

    “Shakedown is just, you drive the car around the track and you basically see what falls off and then you know what you need to fix,” Mehrotra explains. “Hopefully nothing too major falls off!”

    The road ahead

    At the conclusion of the race, Mehotra officially stepped down and handed SEVT’s reins to its new leaders: Kotesh will take the helm as team captain, and rising sophomore Sydney Kim, an ocean engineering major, will serve as vice-captain. The long drive back from the Midwest gave them time to reflect on the win and future plans.

    Although Nimbus performed well, there were a few instructive glitches here and there, mostly during scrutineering. But there was nothing the team couldn’t handle. For example, the canopy latch didn’t always hold, so the clear acrylic bubble covering the driver would pop open. (A little spring adjustment and tape did the trick.) In addition, Nimbus had a tendency to skid when the driver slammed on the brakes. (Driver training, and letting some air out of the tires, improved the traction.)

    Then there were the unpredictable variables, beyond the team’s control. On one day, with little sun, Nimbus had to chug along the highway at a mere 15 miles per hour. And there was the time that the Kansas State Police pulled the entire caravan over. “They didn’t realize we were coming through,” Mehrotra explains.

    Kim thinks one of the keys to the team’s success is that Nimbus is quite reliable. “We didn’t have wheels falling off on the road. Once we got the car rolling, things didn’t go wrong mechanically or electrically. Also, it’s very energy efficient because it’s lightweight and the shape of the vehicle is very aerodynamic. On a nice sunny day, it allows us to drive 40 miles per hour energy-neutral — the battery stays at the same amount of charge as we drive,” she says.

    The next ASC will take place in 2022, so this year the team will focus on refining Nimbus to race it again next summer. Also, they’ve set their sights on building a car to enter in the Multiple Occupancy Vehicle (MOV) class in the 2024 race — something the team has never done. “It will definitely take the three years to build a good car to compete,” Kotesh muses. “But it’s a really good transition period, after doing so well on this race, so our team is excited about it.”

    “It will be challenging for them, but I wouldn’t put it anything past them,” says Patrick McAtamney, the Edgerton Center technical instructor and shop manager who works with all the student clubs and teams, from solar vehicles to Formula race cars to rockets. He attended ASC, too, and has the utmost admiration for SEVT. “It’s totally student-run. They do all the designing and machining themselves. I always tell people that sometimes I feel like my only job is to make sure they have 10 fingers when they leave the shop.”

    In the meantime, before the school year begins, SEVT has another challenge: deciding where to put the trophy. “It’s huge,” McAtamney says. “It’s about the size of the Stanley Cup!” More

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    Using aluminum and water to make clean hydrogen fuel — when and where it’s needed

    As the world works to move away from fossil fuels, many researchers are investigating whether clean hydrogen fuel can play an expanded role in sectors from transportation and industry to buildings and power generation. It could be used in fuel cell vehicles, heat-producing boilers, electricity-generating gas turbines, systems for storing renewable energy, and more.

    But while using hydrogen doesn’t generate carbon emissions, making it typically does. Today, almost all hydrogen is produced using fossil fuel-based processes that together generate more than 2 percent of all global greenhouse gas emissions. In addition, hydrogen is often produced in one location and consumed in another, which means its use also presents logistical challenges.

    A promising reaction

    Another option for producing hydrogen comes from a perhaps surprising source: reacting aluminum with water. Aluminum metal will readily react with water at room temperature to form aluminum hydroxide and hydrogen. That reaction doesn’t typically take place because a layer of aluminum oxide naturally coats the raw metal, preventing it from coming directly into contact with water.

    Using the aluminum-water reaction to generate hydrogen doesn’t produce any greenhouse gas emissions, and it promises to solve the transportation problem for any location with available water. Simply move the aluminum and then react it with water on-site. “Fundamentally, the aluminum becomes a mechanism for storing hydrogen — and a very effective one,” says Douglas P. Hart, professor of mechanical engineering at MIT. “Using aluminum as our source, we can ‘store’ hydrogen at a density that’s 10 times greater than if we just store it as a compressed gas.”

    Two problems have kept aluminum from being employed as a safe, economical source for hydrogen generation. The first problem is ensuring that the aluminum surface is clean and available to react with water. To that end, a practical system must include a means of first modifying the oxide layer and then keeping it from re-forming as the reaction proceeds.

    The second problem is that pure aluminum is energy-intensive to mine and produce, so any practical approach needs to use scrap aluminum from various sources. But scrap aluminum is not an easy starting material. It typically occurs in an alloyed form, meaning that it contains other elements that are added to change the properties or characteristics of the aluminum for different uses. For example, adding magnesium increases strength and corrosion-resistance, adding silicon lowers the melting point, and adding a little of both makes an alloy that’s moderately strong and corrosion-resistant.

    Despite considerable research on aluminum as a source of hydrogen, two key questions remain: What’s the best way to prevent the adherence of an oxide layer on the aluminum surface, and how do alloying elements in a piece of scrap aluminum affect the total amount of hydrogen generated and the rate at which it is generated?

    “If we’re going to use scrap aluminum for hydrogen generation in a practical application, we need to be able to better predict what hydrogen generation characteristics we’re going to observe from the aluminum-water reaction,” says Laureen Meroueh PhD ’20, who earned her doctorate in mechanical engineering.

    Since the fundamental steps in the reaction aren’t well understood, it’s been hard to predict the rate and volume at which hydrogen forms from scrap aluminum, which can contain varying types and concentrations of alloying elements. So Hart, Meroueh, and Thomas W. Eagar, a professor of materials engineering and engineering management in the MIT Department of Materials Science and Engineering, decided to examine — in a systematic fashion — the impacts of those alloying elements on the aluminum-water reaction and on a promising technique for preventing the formation of the interfering oxide layer.

    To prepare, they had experts at Novelis Inc. fabricate samples of pure aluminum and of specific aluminum alloys made of commercially pure aluminum combined with either 0.6 percent silicon (by weight), 1 percent magnesium, or both — compositions that are typical of scrap aluminum from a variety of sources. Using those samples, the MIT researchers performed a series of tests to explore different aspects of the aluminum-water reaction.

    Pre-treating the aluminum

    The first step was to demonstrate an effective means of penetrating the oxide layer that forms on aluminum in the air. Solid aluminum is made up of tiny grains that are packed together with occasional boundaries where they don’t line up perfectly. To maximize hydrogen production, researchers would need to prevent the formation of the oxide layer on all those interior grain surfaces.

    Research groups have already tried various ways of keeping the aluminum grains “activated” for reaction with water. Some have crushed scrap samples into particles so tiny that the oxide layer doesn’t adhere. But aluminum powders are dangerous, as they can react with humidity and explode. Another approach calls for grinding up scrap samples and adding liquid metals to prevent oxide deposition. But grinding is a costly and energy-intensive process.

    To Hart, Meroueh, and Eagar, the most promising approach — first introduced by Jonathan Slocum ScD ’18 while he was working in Hart’s research group — involved pre-treating the solid aluminum by painting liquid metals on top and allowing them to permeate through the grain boundaries.

    To determine the effectiveness of that approach, the researchers needed to confirm that the liquid metals would reach the internal grain surfaces, with and without alloying elements present. And they had to establish how long it would take for the liquid metal to coat all of the grains in pure aluminum and its alloys.

    They started by combining two metals — gallium and indium — in specific proportions to create a “eutectic” mixture; that is, a mixture that would remain in liquid form at room temperature. They coated their samples with the eutectic and allowed it to penetrate for time periods ranging from 48 to 96 hours. They then exposed the samples to water and monitored the hydrogen yield (the amount formed) and flow rate for 250 minutes. After 48 hours, they also took high-magnification scanning electron microscope (SEM) images so they could observe the boundaries between adjacent aluminum grains.

    Based on the hydrogen yield measurements and the SEM images, the MIT team concluded that the gallium-indium eutectic does naturally permeate and reach the interior grain surfaces. However, the rate and extent of penetration vary with the alloy. The permeation rate was the same in silicon-doped aluminum samples as in pure aluminum samples but slower in magnesium-doped samples.

    Perhaps most interesting were the results from samples doped with both silicon and magnesium — an aluminum alloy often found in recycling streams. Silicon and magnesium chemically bond to form magnesium silicide, which occurs as solid deposits on the internal grain surfaces. Meroueh hypothesized that when both silicon and magnesium are present in scrap aluminum, those deposits can act as barriers that impede the flow of the gallium-indium eutectic.

    The experiments and images confirmed her hypothesis: The solid deposits did act as barriers, and images of samples pre-treated for 48 hours showed that permeation wasn’t complete. Clearly, a lengthy pre-treatment period would be critical for maximizing the hydrogen yield from scraps of aluminum containing both silicon and magnesium.

    Meroueh cites several benefits to the process they used. “You don’t have to apply any energy for the gallium-indium eutectic to work its magic on aluminum and get rid of that oxide layer,” she says. “Once you’ve activated your aluminum, you can drop it in water, and it’ll generate hydrogen — no energy input required.” Even better, the eutectic doesn’t chemically react with the aluminum. “It just physically moves around in between the grains,” she says. “At the end of the process, I could recover all of the gallium and indium I put in and use it again” — a valuable feature as gallium and (especially) indium are costly and in relatively short supply.

    Impacts of alloying elements on hydrogen generation

    The researchers next investigated how the presence of alloying elements affects hydrogen generation. They tested samples that had been treated with the eutectic for 96 hours; by then, the hydrogen yield and flow rates had leveled off in all the samples.

    The presence of 0.6 percent silicon increased the hydrogen yield for a given weight of aluminum by 20 percent compared to pure aluminum — even though the silicon-containing sample had less aluminum than the pure aluminum sample. In contrast, the presence of 1 percent magnesium produced far less hydrogen, while adding both silicon and magnesium pushed the yield up, but not to the level of pure aluminum.

    The presence of silicon also greatly accelerated the reaction rate, producing a far higher peak in the flow rate but cutting short the duration of hydrogen output. The presence of magnesium produced a lower flow rate but allowed the hydrogen output to remain fairly steady over time. And once again, aluminum with both alloying elements produced a flow rate between that of magnesium-doped and pure aluminum.

    Those results provide practical guidance on how to adjust the hydrogen output to match the operating needs of a hydrogen-consuming device. If the starting material is commercially pure aluminum, adding small amounts of carefully selected alloying elements can tailor the hydrogen yield and flow rate. If the starting material is scrap aluminum, careful choice of the source can be key. For high, brief bursts of hydrogen, pieces of silicon-containing aluminum from an auto junkyard could work well. For lower but longer flows, magnesium-containing scraps from the frame of a demolished building might be better. For results somewhere in between, aluminum containing both silicon and magnesium should work well; such material is abundantly available from scrapped cars and motorcycles, yachts, bicycle frames, and even smartphone cases.

    It should also be possible to combine scraps of different aluminum alloys to tune the outcome, notes Meroueh. “If I have a sample of activated aluminum that contains just silicon and another sample that contains just magnesium, I can put them both into a container of water and let them react,” she says. “So I get the fast ramp-up in hydrogen production from the silicon and then the magnesium takes over and has that steady output.”

    Another opportunity for tuning: Reducing grain size

    Another practical way to affect hydrogen production could be to reduce the size of the aluminum grains — a change that should increase the total surface area available for reactions to occur.

    To investigate that approach, the researchers requested specially customized samples from their supplier. Using standard industrial procedures, the Novelis experts first fed each sample through two rollers, squeezing it from the top and bottom so that the internal grains were flattened. They then heated each sample until the long, flat grains had reorganized and shrunk to a targeted size.

    In a series of carefully designed experiments, the MIT team found that reducing the grain size increased the efficiency and decreased the duration of the reaction to varying degrees in the different samples. Again, the presence of particular alloying elements had a major effect on the outcome.

    Needed: A revised theory that explains observations

    Throughout their experiments, the researchers encountered some unexpected results. For example, standard corrosion theory predicts that pure aluminum will generate more hydrogen than silicon-doped aluminum will — the opposite of what they observed in their experiments.

    To shed light on the underlying chemical reactions, Hart, Meroueh, and Eagar investigated hydrogen “flux,” that is, the volume of hydrogen generated over time on each square centimeter of aluminum surface, including the interior grains. They examined three grain sizes for each of their four compositions and collected thousands of data points measuring hydrogen flux.

    Their results show that reducing grain size has significant effects. It increases the peak hydrogen flux from silicon-doped aluminum as much as 100 times and from the other three compositions by 10 times. With both pure aluminum and silicon-containing aluminum, reducing grain size also decreases the delay before the peak flux and increases the rate of decline afterward. With magnesium-containing aluminum, reducing the grain size brings about an increase in peak hydrogen flux and results in a slightly faster decline in the rate of hydrogen output. With both silicon and magnesium present, the hydrogen flux over time resembles that of magnesium-containing aluminum when the grain size is not manipulated. When the grain size is reduced, the hydrogen output characteristics begin to resemble behavior observed in silicon-containing aluminum. That outcome was unexpected because when silicon and magnesium are both present, they react to form magnesium silicide, resulting in a new type of aluminum alloy with its own properties.

    The researchers stress the benefits of developing a better fundamental understanding of the underlying chemical reactions involved. In addition to guiding the design of practical systems, it might help them find a replacement for the expensive indium in their pre-treatment mixture. Other work has shown that gallium will naturally permeate through the grain boundaries of aluminum. “At this point, we know that the indium in our eutectic is important, but we don’t really understand what it does, so we don’t know how to replace it,” says Hart.

    But already Hart, Meroueh, and Eagar have demonstrated two practical ways of tuning the hydrogen reaction rate: by adding certain elements to the aluminum and by manipulating the size of the interior aluminum grains. In combination, those approaches can deliver significant results. “If you go from magnesium-containing aluminum with the largest grain size to silicon-containing aluminum with the smallest grain size, you get a hydrogen reaction rate that differs by two orders of magnitude,” says Meroueh. “That’s huge if you’re trying to design a real system that would use this reaction.”

    This research was supported through the MIT Energy Initiative by ExxonMobil-MIT Energy Fellowships awarded to Laureen Meroueh PhD ’20 from 2018 to 2020.

    This article appears in the Spring 2021 issue of Energy Futures, the magazine of the MIT Energy Initiative.  More

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    Electrifying cars and light trucks to meet Paris climate goals

    On Aug. 5, the White House announced that it seeks to ensure that 50 percent of all new passenger vehicles sold in the United States by 2030 are powered by electricity. The purpose of this target is to enable the U.S to remain competitive with China in the growing electric vehicle (EV) market and meet its international climate commitments. Setting ambitious EV sales targets and transitioning to zero-carbon power sources in the United States and other nations could lead to significant reductions in carbon dioxide and other greenhouse gas emissions in the transportation sector and move the world closer to achieving the Paris Agreement’s long-term goal of keeping global warming well below 2 degrees Celsius relative to preindustrial levels.

    At this time, electrification of the transportation sector is occurring primarily in private light-duty vehicles (LDVs). In 2020, the global EV fleet exceeded 10 million, but that’s a tiny fraction of the cars and light trucks on the road. How much of the LDV fleet will need to go electric to keep the Paris climate goal in play? 

    To help answer that question, researchers at the MIT Joint Program on the Science and Policy of Global Change and MIT Energy Initiative have assessed the potential impacts of global efforts to reduce carbon dioxide emissions on the evolution of LDV fleets over the next three decades.

    Using an enhanced version of the multi-region, multi-sector MIT Economic Projection and Policy Analysis (EPPA) model that includes a representation of the household transportation sector, they projected changes for the 2020-50 period in LDV fleet composition, carbon dioxide emissions, and related impacts for 18 different regions. Projections were generated under four increasingly ambitious climate mitigation scenarios: a “Reference” scenario based on current market trends and fuel efficiency policies, a “Paris Forever” scenario in which current Paris Agreement commitments (Nationally Determined Contributions, or NDCs) are maintained but not strengthened after 2030, a “Paris to 2 C” scenario in which decarbonization actions are enhanced to be consistent with capping global warming at 2 C, and an “Accelerated Actions” scenario the caps global warming at 1.5 C through much more aggressive emissions targets than the current NDCs.

    Based on projections spanning the first three scenarios, the researchers found that the global EV fleet will likely grow to about 95-105 million EVs by 2030, and 585-823 million EVs by 2050. In the Accelerated Actions scenario, global EV stock reaches more than 200 million vehicles in 2030, and more than 1 billion in 2050, accounting for two-thirds of the global LDV fleet. The research team also determined that EV uptake will likely grow but vary across regions over the 30-year study time frame, with China, the United States, and Europe remaining the largest markets. Finally, the researchers found that while EVs play a role in reducing oil use, a more substantial reduction in oil consumption comes from economy-wide carbon pricing. The results appear in a study in the journal Economics of Energy & Environmental Policy.

    “Our study shows that EVs can contribute significantly to reducing global carbon emissions at a manageable cost,” says MIT Joint Program Deputy Director and MIT Energy Initiative Senior Research Scientist Sergey Paltsev, the lead author. “We hope that our findings will help decision-makers to design efficient pathways to reduce emissions.”  

    To boost the EV share of the global LDV fleet, the study’s co-authors recommend more ambitious policies to mitigate climate change and decarbonize the electric grid. They also envision an “integrated system approach” to transportation that emphasizes making internal combustion engine vehicles more efficient, a long-term shift to low- and net-zero carbon fuels, and systemic efficiency improvements through digitalization, smart pricing, and multi-modal integration. While the study focuses on EV deployment, the authors also stress for the need for investment in all possible decarbonization options related to transportation, including enhancing public transportation, avoiding urban sprawl through strategic land-use planning, and reducing the use of private motorized transport by mode switching to walking, biking, and mass transit.

    This research is an extension of the authors’ contribution to the MIT Mobility of the Future study. More

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    Chemistry Undergraduate Teaching Lab hibernates fume hoods, drastically reducing energy costs

    The Department of Chemistry’s state-of-the-art Undergraduate Teaching Lab (UGTL), which opened on the fifth floor of MIT.nano in fall 2018, is home to 69 fume hoods. The hoods, ranging from four to seven feet wide, protect students and staff from potential exposure to hazardous materials while working in the lab. Fume hoods represent a tremendous energy consumption on the MIT campus; in addition to the energy required to operate them, the air that replaces what is exhausted must be heated or cooled. Thus, any lab with a large number of fume hoods is destined to be faced with high operational energy cost.

    “When the UGTL’s fume hoods are in use, the air-change rates — the number of times fresh air is exchanged in the space in a given time frame — averages between 25 and 30 air changes per hour (ACH),” says Nicole Imbergamo, senior sustainability project manager in MIT Campus Construction. “When the lab is unoccupied, that air-change rate averages 11 ACH. For context, in a laboratory with a single fume hood, typically MIT’s EHS [Environment, Health, and Safety] department would require six ACH when occupied and four ACH when unoccupied. Hibernation of the fume hoods allowed us to close the gap between the current unoccupied air-change rate and what is typical on campus in a non-teaching lab environment.”

    Fifty-eight of the 69 fume hoods in the UGTL are consistently unused between the hours of 6:30 p.m. and 12 p.m., as well as all weekend long, totaling 135 hours per week. Based on these numbers, the team determined it was safe to “hibernate” the fume hoods during the off hours, saving the Institute on fan energy and the cost of heating and cooling the air that gets flushed into each hood.

    John Dolhun PhD ’73 is the director of the UGTL. “The project started when MIT Green Labs — a division of the Environment, Health, and Safety Office now known as the Safe & Sustainable Labs Program — contacted the UGTL in October 2018, followed by an initial meeting in November 2018 with all the key players, including Safe and Sustainable Labs, the EHS Office, the Department of Facilities, and the Department of Chemistry,” says Dolhun. “It was during these initial discussions that the UGTL recognized this was something we had to do. The project was completed in April 2021.”

    Now, through a scheduled time clock in the Building Management System (BMS), the 58 fume hoods are flipped into hibernation mode at the end of each day. “In hibernation mode, the exhaust air valves go to their minimum airflow, which is lower than a fume hood minimum required when in use,” says Imbergamo. “As a safety feature, if the sash of a fume hood is opened while it is in standby mode, the valve and hood are automatically released from hibernation until the next scheduled time.” The BMS allows Dolhun and all with access to instantly view the hibernation status of every hood online, at any time, from any location. As an additional safety measure, the lab is equipped with an emergency kill switch that, when activated, instantly takes all 58 fume hoods out of hibernation, increasing the air changes per hour by about 37 percent, at one touch.

    The MIT operations team worked with the building controls vendor to create graphics that allow the UGTL users to easily see the hood sash positions and their current status as either hibernated or in normal operating mode. This virtual visibility allows the UGTL team to confirm the hoods are all closed before leaving the lab at the end of each day, and to confirm the energy reductions. This visual access also lends itself to educating the students on the importance of closing the sash at the end of their lab work, and gives an opportunity for educating the students on relevant fume hood management best practices that will serve them far beyond their undergraduate chemistry classes.

    Since employing the use of hibernation mode, the unoccupied UGTL air change rate has plummeted from 11 ACH to seven ACH, drastically shrinking unnecessary energy outflow, saving MIT an estimated $21,000 per year. The annual utility cost savings of both reduced supply and exhaust fan energy, as well as the heating and cooling required of the supply air to the space, will result in a less-than three-year payback for MIT. The overall success of the hood hibernation program, and the savings that it has afforded the UGTL, is very motivational for the Green Initiative. The highlights of this system will be shared with other labs, both at MIT and beyond, that may also benefit from similar adjustments. More

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    Cleaning up industrial filtration

    If you wanted to get pasta out of a pot of water, would you boil off the water, or use a strainer? While home cooks would choose the strainer, many industries continue to use energy-intensive thermal methods of separating out liquids. In some cases, that’s because it’s difficult to make a filtration system for chemical separation, which requires pores small enough to separate atoms.

    In other cases, membranes exist to separate liquids, but they are made of fragile polymers, which can break down or gum up in industrial use.

    Via Separations, a startup that emerged from MIT in 2017, has set out to address these challenges with a membrane that is cost-effective and robust. Made of graphene oxide (a “cousin” of pencil lead), the membrane can reduce the amount of energy used in industrial separations by 90 percent, according to Shreya Dave PhD ’16, company co-founder and CEO.

    This is valuable because separation processes account for about 22 percent of all in-plant energy use in the United States, according to Oak Ridge National Laboratory. By making such processes significantly more efficient, Via Separations plans to both save energy and address the significant emissions produced by thermal processes. “Our goal is eliminating 500 megatons of carbon dioxide emissions by 2050,” Dave says.

    Play video

    What do our passions for pasta and decarbonizing the Earth have in common? MIT alumna Shreya Dave PhD ’16 explains how she and her team at Via Separations are building the equivalent of a pasta strainer to separate chemical compounds for industry.

    Via Separations began piloting its technology this year at a U.S. paper company and expects to deploy a full commercial system there in the spring of 2022. “Our vision is to help manufacturers slow carbon dioxide emissions next year,” Dave says.

    MITEI Seed Grant

    The story of Via Separations begins in 2012, when the MIT Energy Initiative (MITEI) awarded a Seed Fund grant to Professor Jeffrey Grossman, who is now the Morton and Claire Goulder and Family Professor in Environmental Systems and head of MIT’s Department of Materials Science and Engineering. Grossman was pursuing research into nanoporous membranes for water desalination. “We thought we could bring down the cost of desalination and improve access to clean water,” says Dave, who worked on the project as a graduate student in Grossman’s lab.

    There, she teamed up with Brent Keller PhD ’16, another Grossman graduate student and a 2016-17 ExxonMobil-MIT Energy Fellow, who was developing lab experiments to fabricate and test new materials. “We were early comrades in figuring out how to debug experiments or fix equipment,” says Keller, Via Separations’ co-founder and chief technology officer. “We were fast friends who spent a lot of time talking about science over burritos.”

    Dave went on to write her doctoral thesis on using graphene oxide for water desalination, but that turned out to be the wrong application of the technology from a business perspective, she says. “The cost of desalination doesn’t lie in the membrane materials,” she explains.

    So, after Dave and Keller graduated from MIT in 2016, they spent a lot of time talking to customers to learn more about the needs and opportunities for their new separation technology. This research led them to target the paper industry, because the environmental benefits of improving paper processing are enormous, Dave says. “The paper industry is particularly exciting because separation processes just in that industry account for more than 2 percent of U.S. energy consumption,” she says. “It’s a very concentrated, high-energy-use industry.”

    Most paper today is made by breaking down the chemical bonds in wood to create wood pulp, the primary ingredient of paper. This process generates a byproduct called black liquor, a toxic solution that was once simply dumped into waterways. To clean up this process, paper mills turned to boiling off the water from black liquor and recovering both water and chemicals for reuse in the pulping process. (Today, the most valuable way to use the liquor is as biomass feedstock to generate energy.) Via Separations plans to accomplish this same separation work by filtering black liquor through its graphene oxide membrane.

    “The advantage of graphene oxide is that it’s very robust,” Dave says. “It’s got carbon double bonds that hold together in a lot of environments, including at different pH levels and temperatures that are typically unfriendly to materials.”

    Such properties should also make the company’s membranes attractive to other industries that use membrane separation, Keller says, because today’s polymer membranes have drawbacks. “For most of the things we make — from plastics to paper and gasoline — those polymers will swell or react or degrade,” he says.

    Graphene oxide is significantly more durable, and Via Separations can customize the pores in the material to suit each industry’s application. “That’s our secret sauce,” Dave says, “modulating pore size while retaining robustness to operate in challenging environments.”

    “We’re building a catalog of products to serve different applications,” Keller says, noting that the next target market could be the food and beverage industry. “In that industry, instead of separating different corrosive paper chemicals from water, we’re trying to separate particular sugars and food ingredients from other things.”

    Future target customers include pharmaceutical companies, oil refineries, and semiconductor manufacturers, or even carbon capture businesses.

    Scaling up

    Dave, Keller, and Grossman launched Via Separations in 2017 — with a lot of help from MIT. After the seed grant, in 2015, the founders received a year of funding and support from the J-WAFS Solutions program to explore markets and to develop their business plans. The company’s first capital investment came from The Engine, a venture firm founded by MIT to support “tough tech” companies (tech businesses with transformative potential but long and challenging paths to success). They also received advice and support from MIT’s Deshpande Center for Technological Innovation, Venture Mentoring Service, and Technology Licensing Office. In addition, Grossman continues to serve the company as chief scientist.

    “We were incredibly fortunate to be starting a company in the MIT entrepreneurial ecosystem,” Keller says, noting that The Engine support alone “probably shaved years off our progress.”

    Already, Via Separations has grown to employ 17 people, while significantly scaling up its product. “Our customers are producing thousands of gallons per minute,” Keller explains. “To process that much liquid, we need huge areas of membrane.”

    Via Separations’ manufacturing process, which is now capable of making more than 10,000 square feet of membrane in one production run, is a key competitive advantage, Dave says. The company rolls 300-400 square feet of membrane into a module, and modules can be combined as needed to increase filtration capacity.

    The goal, Dave says, is to contribute to a more sustainable world by making an environmentally beneficial product that makes good business sense. “What we do is make manufacturing things more energy-efficient,” she says. “We allow a paper mill or chemical facility to make more product using less energy and with lower costs. So, there is a bottom-line benefit that’s significant on an industrial scale.”

    Keller says he shares Dave’s goal of building a more sustainable future. “Climate change and energy are central challenges of our time,” he says. “Working on something that has a chance to make a meaningful impact on something so important to everyone is really fulfilling.”

    This article appears in the Spring 2021 issue of Energy Futures, the magazine of the MIT Energy Initiative.  More

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    Vapor-collection technology saves water while clearing the air

    About two-fifths of all the water that gets withdrawn from lakes, rivers, and wells in the U.S. is used not for agriculture, drinking, or sanitation, but to cool the power plants that provide electricity from fossil fuels or nuclear power. Over 65 percent of these plants use evaporative cooling, leading to huge white plumes that billow from their cooling towers, which can be a nuisance and, in some cases, even contribute to dangerous driving conditions.

    Now, a small company based on technology recently developed at MIT by the Varanasi Research Group is hoping to reduce both the water needs at these plants and the resultant plumes — and to potentially help alleviate water shortages in areas where power plants put pressure on local water systems.

    The technology is surprisingly simple in principle, but developing it to the point where it can now be tested at full scale on industrial plants was a more complex proposition. That required the real-world experience that the company’s founders gained from installing prototype systems, first on MIT’s natural-gas-powered cogeneration plant and then on MIT’s nuclear research reactor.

    In these demanding tests, which involved exposure to not only the heat and vibrations of a working industrial plant but also the rigors of New England winters, the system proved its effectiveness at both eliminating the vapor plume and recapturing water. And, it purified the water in the process, so that it was 100 times cleaner than the incoming cooling water. The system is now being prepared for full-scale tests in a commercial power plant and in a chemical processing plant.

    “Campus as a living laboratory”

    The technology was originally envisioned by professor of mechanical engineering Kripa Varanasi to develop efficient water-recovery systems by capturing water droplets from both natural fog and plumes from power plant cooling towers. The project began as part of doctoral thesis research of Maher Damak PhD ’18, with funding from the MIT Tata Center for Technology and Design, to improve the efficiency of fog-harvesting systems like the ones used in some arid coastal regions as a source of potable water. Those systems, which generally consist of plastic or metal mesh hung vertically in the path of fogbanks, are extremely inefficient, capturing only about 1 to 3 percent of the water droplets that pass through them.

    Varanasi and Damak found that vapor collection could be made much more efficient by first zapping the tiny droplets of water with a beam of electrically charged particles, or ions, to give each droplet a slight electric charge. Then, the stream of droplets passes through a wire mesh, like a window screen, that has an opposite electrical charge. This causes the droplets to be strongly attracted to the mesh, where they fall away due to gravity and can be collected in trays placed below the mesh.

    Lab tests showed the concept worked, and the researchers, joined by Karim Khalil PhD ’18, won the MIT $100K Entrepreneurship Competition in 2018 for the basic concept. The nascent company, which they called Infinite Cooling, with Damak as CEO, Khalil as CTO, and Varanasi as chairperson, immediately went to work setting up a test installation on one of the cooling towers of MIT’s natural-gas-powered Central Utility Plant, with funding from the MIT Office of Sustainability. After experimenting with various configurations, they were able to show that the system could indeed eliminate the plume and produce water of high purity.

    Professor Jacopo Buongiorno in the Department of Nuclear Science and Engineering immediately spotted a good opportunity for collaboration, offering the use of MIT’s Nuclear Reactor Laboratory research facility for further testing of the system with the help of NRL engineer Ed Block. With its 24/7 operation and its higher-temperature vapor emissions, the plant would provide a more stringent real-world test of the system, as well as proving its effectiveness in an actual operating reactor licensed by the Nuclear Regulatory Commission, an important step in “de-risking” the technology so that electric utilities could feel confident in adopting the system.

    After the system was installed above one of the plant’s four cooling towers, testing showed that the water being collected was more than 100 times cleaner than the feedwater coming into the cooling system. It also proved that the installation — which, unlike the earlier version, had its mesh screens mounted vertically, parallel to the vapor stream — had no effect at all on the operation of the plant. Video of the tests dramatically illustrates how as soon as the power is switched on to the collecting mesh, the white plume of vapor immediately disappears completely.

    The high temperature and volume of the vapor plume from the reactor’s cooling towers represented “kind of a worst-case scenario in terms of plumes,” Damak says, “so if we can capture that, we can basically capture anything.”

    Working with MIT’s Nuclear Reactor Laboratory, Varanasi says, “has been quite an important step because it helped us to test it at scale. … It really both validated the water quality and the performance of the system.” The process, he says, “shows the importance of using the campus as a living laboratory. It allows us to do these kinds of experiments at scale, and also showed the ability to sustainably reduce the water footprint of the campus.”

    Far-reaching benefits

    Power plant plumes are often considered an eyesore and can lead to local opposition to new power plants because of the potential for obscured views, and even potential traffic hazards when the obscuring plumes blow across roadways. “The ability to eliminate the plumes could be an important benefit, allowing plants to be sited in locations that might otherwise be restricted,” Buongiorno says. At the same time, the system could eliminate a significant amount of water used by the plants and then lost to the sky, potentially alleviating pressure on local water systems, which could be especially helpful in arid regions.

    The system is essentially a distillation process, and the pure water it produces could go into power plant boilers — which are separate from the cooling system — that require high-purity water. That might reduce the need for both fresh water and purification systems for the boilers.

    What’s more, in many arid coastal areas power plants are cooled directly with seawater. This system would essentially add a water desalination capability to the plant, at a fraction of the cost of building a new standalone desalination plant, and at an even smaller fraction of its operating costs since the heat would essentially be provided for free.

    Contamination of water is typically measured by testing its electrical conductivity, which increases with the amount of salts and other contaminants it contains. Water used in power plant cooling systems typically measures 3,000 microsiemens per centimeter, Khalil explains, while the water supply in the City of Cambridge is typically around 500 or 600 microsiemens per centimeter. The water captured by this system, he says, typically measures below 50 microsiemens per centimeter.

    Thanks to the validation provided by the testing on MIT’s plants, the company has now been able to secure arrangements for its first two installations on operating commercial plants, which should begin later this year. One is a 900-megawatt power plant where the system’s clean water production will be a major advantage, and the other is at a chemical manufacturing plant in the Midwest.

    In many locations power plants have to pay for the water they use for cooling, Varanasi says, and the new system is expected to reduce the need for water by up to 20 percent. For a typical power plant, that alone could account for about a million dollars saved in water costs per year, he says.

    “Innovation has been a hallmark of the U.S. commercial industry for more than six decades,” says Maria G. Korsnick, president and CEO of the Nuclear Energy Institute, who was not involved in the research. “As the changing climate impacts every aspect of life, including global water supplies, companies across the supply chain are innovating for solutions. The testing of this innovative technology at MIT provides a valuable basis for its consideration in commercial applications.” More