Assistant professor in EECS and DMSE is developing materials with novel structures and useful applications, including renewable energy and information storage.

 

Ceramics research Jennifer Rupp headshot MIT Webm
Jennifer Rupp's current ceramics research applications range from battery-based storage for renewable energy, to energy-harvesting systems, to devices used to store data during computation. Photo courtesy of Jennifer Rupp.

Ensuring that her research contributes to society’s well-being is a major driving force for Jennifer Rupp.

“Even if my work is fundamental, I want to think about how it can be useful for society,” says Rupp, the Thomas Lord Assistant Professor of Materials Science and Engineering and an assistant professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT.

Since joining the Department of Materials Science and Engineering in February 2017, she has been focusing not only on the basics of ceramics processing techniques but also on how to further develop those techniques to design new practical devices as well as materials with novel structures. Her current research applications range from battery-based storage for renewable energy, to energy-harvesting systems, to devices used to store data during computation.

Rupp first became intrigued with ceramics during her doctoral studies at ETH Zurich.

“I got particularly interested in how they can influence structures to gain certain functionalities and properties,” she says. During this time, she also became fascinated with how ceramics can contribute to the conversion and storage of energy. The need to transition to a low-carbon energy future motivates much of her work at MIT. “Climate change is happening,” she says. “Even though not everybody may agree on that, it’s a fact.”

One way to tackle the climate change problem is by capitalizing on solar energy. Sunshine falling on the Earth delivers roughly 170,000 terawatts per year — about 10,000 times the energy consumed annually worldwide. “So we have a lot of solar energy,” says Rupp. “The question is, how do we profit the most from it?”

To help convert that solar energy into a renewable fuel, her team is designing a ceramic material that can be used in a solar reactor in which incoming sunlight is controlled to create a heat cycle. During the temperature shifts, the ceramic material incorporates and releases oxygen. At the higher temperature, it loses oxygen; at the lower temperature, it regains the oxygen. When carbon dioxide and water are flushed into the solar reactor during this oxidation process, a split reaction occurs, yielding a combination of carbon monoxide and hydrogen known as syngas, which can be converted catalytically into ethanol, methanol, or other liquid fuels.

While the challenges are many, Rupp says she feels bolstered by the humanitarian ethos at MIT. “At MIT, there are scientists and engineers who care about social issues and try to contribute with science and their problem-solving skills to do more,” she says. “I think this is quite important. MIT gives you strong support to try out even very risky things.”

In addition to continuing her work on new materials, Rupp looks forward to exploring new concepts with her students. During the fall of 2017, she taught two recitation sections of 3.091 (Introduction to Solid State Chemistry), a class that has given thousands of MIT undergraduates a foundation in chemistry from an engineering perspective. This spring, she will begin teaching a new elective for graduate students on ceramics processing and engineering that will delve into making ceramic materials not only on the conventional large-scale level but also as nanofabricated structures and small-system structures for devices that can store and convert energy, compute information, or sense carbon dioxide or various environmental pollutants.

To further engage with students, Rupp has proposed an extracurricular club for them to develop materials science comic strips. The first iteration is available on Instagram (@materialcomics) and it depicts three heroes who jump into various structures to investigate their composition and, naturally, to have adventures. Rupp sees the comics as an exciting avenue to engage the nonscientific community as a whole and to illustrate the structures and compositions of various everyday materials.

“I think it is important to create interest in the topic of materials science across various ages and simply to enjoy the fun in it,” she says.

Rupp says MIT is proving to be a stimulating environment. “Everybody is really committed and open to being creative,” she says. “I think a scientist is not only a teacher or a student; a scientist is someone of any age, of any rank, someone who simply enjoys unlocking creativity to design new materials and devices.”

This article appears in the Autumn 2017 issue of Energy Futures, the magazine of the MIT Energy Initiative.

Kelley Travers | MIT Energy Initiative
MIT News Office, February 9, 2018

Approach could bypass the time-consuming steps currently needed to test new photovoltaic materials.
MIT Assessing PVs Web
This experimental setup was used by the team to measure the electrical output of a sample of solar cell material, under controlled conditions of varying temperature and illumination. The data from those tests was then used as the basis for computer modeling using statistical methods to predict the overall performance of the material in real-world operating conditions. Image, Riley Brandt

The worldwide quest by researchers to find better, more efficient materials for tomorrow’s solar panels is usually slow and painstaking. Researchers typically must produce lab samples — which are often composed of multiple layers of different materials bonded together — for extensive testing.

Now, a team at MIT and other institutions has come up with a way to bypass such expensive and time-consuming fabrication and testing, allowing for a rapid screening of far more variations than would be practical through the traditional approach.

The new process could not only speed up the search for new formulations, but also do a more accurate job of predicting their performance, explains Rachel Kurchin, an MIT graduate student and co-author of a paper describing the new process that appears this week in the journal Joule. Traditional methods “often require you to make a specialized sample, but that differs from an actual cell and may not be fully representative” of a real solar cell’s performance, she says.

For example, typical testing methods show the behavior of the “majority carriers,” the predominant particles or vacancies whose movement produces an electric current through a material. But in the case of photovoltaic (PV) materials, Kurchin explains, it is actually the minority carriers — those that are far less abundant in the material — that are the limiting factor in a device’s overall efficiency, and those are much more difficult to measure. In addition, typical procedures only measure the flow of current in one set of directions — within the plane of a thin-film material — whereas it’s up-down flow that is actually harnessed in a working solar cell. In many materials, that flow can be “drastically different,” making it critical to understand in order to properly characterize the material, she says.

“Historically, the rate of new materials development is slow — typically 10 to 25 years,” says Tonio Buonassisi, an associate professor of mechanical engineering at MIT and senior author of the paper. “One of the things that makes the process slow is the long time it takes to troubleshoot early-stage prototype devices,” he says. “Performing characterization takes time — sometimes weeks or months — and the measurements do not always have the necessary sensitivity to determine the root cause of any problems.”

So, Buonassisi says, “the bottom line is, if we want to accelerate the pace of new materials development, it is imperative that we figure out faster and more accurate ways to troubleshoot our early-stage materials and prototype devices.” And that’s what the team has now accomplished. They have developed a set of tools that can be used to make accurate, rapid assessments of proposed materials, using a series of relatively simple lab tests combined with computer modeling of the physical properties of the material itself, as well as additional modeling based on a statistical method known as Bayesian inference.

The system involves making a simple test device, then measuring its current output under different levels of illumination and different voltages, to quantify exactly how the performance varies under these changing conditions. These values are then used to refine the statistical model.

“After we acquire many current-voltage measurements [of the sample] at different temperatures and illumination intensities, we need to figure out what combination of materials and interface variables make the best fit with our set of measurements,” Buonassisi explains. “Representing each parameter as a probability distribution allows us to account for experimental uncertainty, and it also allows us to suss out which parameters are covarying.”

The Bayesian inference process allows the estimates of each parameter to be updated based on each new measurement, gradually refining the estimates and homing in ever closer to the precise answer, he says.

In seeking a combination of materials for a particular kind of application, Kurchin says, “we put in all these materials properties and interface properties, and it will tell you what the output will look like.”

The system is simple enough that, even for materials that have been less well-characterized in the lab, “we’re still able to run this without tremendous computer overhead.” And, Kurchin says, making use of the computational tools to screen possible materials will be increasingly useful because “lab equipment has gotten more expensive, and computers have gotten cheaper. This method allows you to minimize your use of complicated lab equipment.”

The basic methodology, Buonassisi says, could be applied to a wide variety of different materials evaluations, not just solar cells — in fact, it may apply to any system that involves a computer model for the output of an experimental measurement. “For example, this approach excels in figuring out which material or interface property might be limiting performance, even for complex stacks of materials like batteries, thermoelectric devices, or composites used in tennis shoes or airplane wings.” And, he adds, “It is especially useful for early-stage research, where many things might be going wrong at once.”

Going forward, he says, “our vision is to link up this fast characterization method with the faster materials and device synthesis methods we’ve developed in our lab.” Ultimately, he says, “I’m very hopeful the combination of high-throughput computing, automation, and machine learning will help us accelerate the rate of novel materials development by more than a factor of five. This could be transformative, bringing the timelines for new materials-science discoveries down from 20 years to about three to five years.”

The research team also included Riley Brandt '11, SM '13, PhD '16; former postdoc Vera Steinmann; MIT graduate student Daniil Kitchaev and visiting professor Gerbrand Ceder, Chris Roat at Google Inc.; and Sergiu Levcenco and Thomas Unold at Hemholz Zentrum in Berlin. The work was supported by a Google Faculty Research Award, the U.S. Department of Energy, and a Total research grant.

David L. Chandler | MIT News Office
December 20, 2017

Friday, 17 November 2017 10:10

A new way to store thermal energy

MIT researchers create material for a chemical heat “battery” that could release its energy on demand.

In large parts of the developing world, people have abundant heat from the sun during the day, but most cooking takes place later in the evening when the sun is down, using fuel — such as wood, brush or dung — that is collected with significant time and effort.

Now, a new chemical composite developed by researchers at MIT could provide an alternative. It could be used to store heat from the sun or any other source during the day in a kind of thermal battery, and it could release the heat when needed, for example for cooking or heating after dark.

A common approach to thermal storage is to use what is known as a phase change material (PCM), where input heat melts the material and its phase change — from solid to liquid — stores energy. When the PCM is cooled back down below its melting point, it turns back into a solid, at which point the stored energy is released as heat. There are many examples of these materials, including waxes or fatty acids used for low-temperature applications, and molten salts used at high temperatures. But all current PCMs require a great deal of insulation, and they pass through that phase change temperature uncontrollably, losing their stored heat relatively rapidly.

Instead, the new system uses molecular switches that change shape in response to light; when integrated into the PCM, the phase-change temperature of the hybrid material can be adjusted with light, allowing the thermal energy of the phase change to be maintained even well below the melting point of the original material.

light activate

This blue LED lamp setup is used to trigger the heat discharge from large-scale films of phase-change materials. (Melanie Gonick/MIT)

The new findings, by MIT postdocs Grace Han and Huashan Li and Professor Jeffrey Grossman, are reported this week in the journal Nature Communications.

“The trouble with thermal energy is, it’s hard to hold onto it,” Grossman explains. So his team developed what are essentially add-ons for traditional phase change materials, or, “little molecules that undergo a structural change when light shines on them.” The trick was to find a way to integrate these molecules with conventional PCM materials to release the stored energy as heat, on demand. “There are so many applications where it would be useful to store thermal energy in a way lets you trigger it when needed,” he says.

The researchers accomplished this by combining the fatty acids with an organic compound that responds to a pulse of light. With this arrangement, the light-sensitive component alters the thermal properties of the other component, which stores and releases its energy. The hybrid material melts when heated, and after being exposed to ultraviolet light, it stays melted even when cooled back down. Next, when triggered by another pulse of light, the material resolidifies and gives back the thermal phase-change energy. 

“By integrating a light-activated molecule into the traditional picture of latent heat, we add a new kind of control knob for properties such as melting, solidification, and supercooling,” says Grossman, who is the Morton and Claire Goulder and Family Professor in Environmental Systems as well as professor of materials science and engineering.

The UV-activated thermal energy storage material shows the rapid crystallization and heat discharge upon visible light (blue LED) illumination. (Grossman Group at MIT)

The system could make use of any source of heat, not just solar, Han says. “The availability of waste heat is widespread, from industrial processes, to solar heat, and even the heat coming out of vehicles, and it’s usually just wasted.” Harnessing some of that waste could provide a way of recycling that heat for useful applications.

crystalization

“What we are doing technically,” Han explains, “is installing a new energy barrier, so the stored heat cannot be released immediately.” In its chemically stored form, the energy can remain for long periods until the optical trigger is activated. In their initial small-scale lab versions, they showed the stored heat can remain stable for at least 10 hours, whereas a device of similar size storing heat directly would dissipate it within a few minutes. And “there’s no fundamental reason why it can’t be tuned to go higher,” Han says.

In the initial proof-of-concept system “the temperature change or supercooling that we achieve for this thermal storage material can be up to 10 degrees C (18 F), and we hope we can go higher,” Grossman says.

Under a dark-field microscope, the microscale environment shows the rapid crystal growth can easily be monitored. (Grossman Group at MIT)

Already, in this version, “the energy density is quite significant, even though we’re using a conventional phase-change material,” Han says. The material can store about 200 joules per gram, which she says is “very good for any organic phase-change material.” And already, “people have shown interest in using this for cooking in rural India,” she says. Such systems could also be used for drying agricultural crops or for space heating.

“Our interest in this work was to show a proof of concept,” Grossman says, “but we believe there is a lot of potential for using light-activated materials to hijack the thermal storage properties of phase change materials.”

“This is highly creative research, where the key is that the scientists combine a thermally driven phase-change material with a photoswitching molecule, to build an energy barrier to stabilize the thermal energy storage,” says Junqiao Wu, a professor of materials science and engineering at the University of California at Berkeley, who was not involved in the research. “I think the work is significant, as it offers a practical way to store thermal energy, which has been challenging in the past.” 

dark field

The work was supported by the Tata Center for Technology and Design within MIT’s Energy Initiative.

David L. Chandler | MIT News Office
November 16, 2017