Summer Scholar Alexandra Oliveira contributes to work on redox flow batteries in Brushett Lab.
Renewable energy technologies such as wind and solar are unpredictable and intermittent, creating a need for batteries to store electricity until it is needed, notes MIT Postdoctoral Associate Antoni Forner-Cuenca. Yet cost-effective technologies have been limited to date.
2017 MPC-CMSE Alexandra Oliveira is working under Forner-Cuenca in the research group of Fikile R. Brushett, the Raymond A. (1921) and Helen E. St. Laurent Career Development Professor of Chemical Engineering at MIT, to improve the chemistry of porous carbon electrodes in one particular type of battery known as a redox flow battery.
“Redox flow batteries are a very promising technology for large-scale energy storage, and, in particular, the work that Alex is doing with us over this summer internship is focusing on modifying the surface chemistry of these porous electrodes,” Forner-Cuenca explains.
During a visit to the lab, Oliveira, who is a junior chemical engineering major at the University of Connecticut, described how liquid electrolytes that are separated by a selective nafion membrane flow through the water-based battery cell and back out. Because the nafion membrane is a selective membrane, ions are exchanged across it, but the two electrolytes circulate in separate halves of the battery. Leads connected to the battery allow the researchers to send through a voltage and then measure the current. “In this case, what we're using it for is to take a capacitance reading, which is an electrochemical property that we can then use to calculate the real surface area. So we want to know the entire area over which we are going to be reacting our electrolyte,” Oliveira says. These electrochemical methods provide valuable information about the material properties like the surface area, Forner-Cuenca says.
Oliveira finds that carbon cloth electrodes, which transmit fluid through open pores, are among the more interesting and successful electrodes. “If you look up to the light, you can see how porous it is,” she says. “So the electrolyte can flow through this much more effectively than some of the other electrodes we have. For her summer project, Oliveira will be growing polymers onto the surface of the carbon electrodes to see if she can change the chemistry of the electrode and then measure the overall performance of the redox flow batteries.
“In a flow battery, the electrolyte flows through the cell,” Oliveira explains. “A lot of research has been done on the electrolytes and active materials but not much on the electrodes themselves. So we’re actually looking at the microstructures of the electrodes and comparing to see what makes the perfect flow cell electrode.”
|2017 MPC-CMSE Summer Scholar Alexandra Oliveira holds a metal connector that goes into a redox flow battery. Oliveira is interning in the Brushett lab this summer, focusing on improving the chemistry of porous carbon electrodes. Photo, Denis Paiste, Materials Processing Center.|
Oliveira’s work focuses on the porosity and permeability of the electrodes. “We’ve been running all sorts of pressure tests to measure permeability, and we are trying to figure out what the surface area of the electrodes is exactly, not just the geometric area on the top, but the area of the electrode that will react electrochemically when we run our flow cell,” she says. Oliveira also plans to use an electrochemical technique called electrographing, in molecules are added to the surface of the electrode in a thin layer. “What we can do then is we can keep the same electrode but we can change the chemical properties of it,” she explains.
Forner-Cuenca suggests that the electrode is the heart of the flow battery in the sense that it has to fulfill different functions. “It needs to be a platform where the liquid electrolyte distributes well, at the same time, electrochemical reactions will happen on the surface of the fibers,” he explains. “So you can imagine that electrode as a very porous, carbonaceous material, which has carbon fibers that are kind of cylinders and the liquid electrolyte will wet those surfaces. The electrons will go from the electrolyte to the carbon fiber, or vice versa, and electrochemical reactions will happen. So you need to have a very selective material. You need to have activity for the products you want, and not secondary reactions, and at the same time it needs to be a material with mechanical edge stability. That means this is going to be inside the flow battery for many years and is going to be compressed under pressure so the electrode also needs to be also mechanically stable. So there are all these different properties that we need to optimize in order to have an advanced flow battery and we are focusing on the electrode in this particular work.”
“What makes redox flow batteries so unique is that they can completely decouple power and energy,” Oliveira explains. “So if you think of your car, in this case, the engine and the fuel tank would be completely separate. So for our purposes, our reactor and our tank control power and energy separately.”
Oliveira’s internship is supported in part by NSF’s Materials Research Science and Engineering Centers program [grant DMR-14-19807]. Participants in the Research Experience for Undergraduates, co-sponsored by the Materials Processing Center and the Center for Materials Science and Engineering, will present their results at a poster session during the last week of the program. The program runs from June 15, 2017, to August 5, 2017, on the MIT campus in Cambridge, Mass.
– Denis Paiste, Materials Processing Center
July 31, 2017
Summer Scholar Lucia Brunel interns under Profs. McKinley and Ribbeck to understand the self-healing properties of mucus and other biological gels.
|2017 MPC-CMSE Summer Scholar Lucia Brunel examines the self-healing properties of biological gels, such as mucus, using an optical tweezer active microrheology setup. Rheology is the study of how materials flow or respond to deformation. The goal of the project is to investigate the dynamics of the self-healing process of mucus and other biological gels. Photo, Denis Paiste, Materials Processing Center|
Biological gels such as mucus and saliva serve many important roles in the body, from acting as barriers to infection to lubricating the eyes and oral cavity. 2017 MPC-CMSE Summer Scholar Lucia Brunel is working on a joint project under Professors Gareth McKinley and Katharina Ribbeck.
“I have a background in traditional polymer science, but I’m really interested in applications to biological systems,” says Brunel, a rising senior at Northwestern University studying chemical and biological engineering. “My project is to investigate the unique self-healing capability that some biological gels have, so I’ve been learning a lot about how to characterize the properties of these biological gels as they heal after damage or deformation.”
MIT graduate student Caroline Wagner, whose doctoral studies focus on investigating the mechanical properties of biological gels, is supervising Brunel’s work in the MIT Bioinstrumentation Lab. “One thing that's still really eluding us is the exact biophysical mechanism for how biological gels self-heal, and the time scale over which this happens.” Wagner says, “For instance, mucus repairs itself very quickly on a regular basis, whether after permitting the passage of sperm or following an event such as a cough or a sneeze, but translating this ability to synthetic materials remains a huge challenge. So when Lucia wanted to join the lab, we thought that focusing on the dynamics of self-healing in biological gels could form the basis for a really interesting summer project.”
Brunel adds that “The design of biomimetic gels comes from an understanding of the properties of the real biological gels, so before making synthetic materials that self-heal, we have to know how biological gels do that. A better understanding of the self-healing abilities of certain biological gels could ultimately lead to the creation of self-healing synthetic materials for use in implantable devices, scaffolds for tissue engineering, or prosthetics, which would be incredible.”
During her summer internship, Brunel has been learning about the technique of rheology, which is the study of how materials flow or respond to deformation. “Rheology is really useful for being able to characterize materials, especially complex fluids like biological gels that have both a viscous component and an elastic component and are somewhere between a liquid and solid,” Brunel says. “I've been doing both micro rheology to tell how the material deforms and recovers on the microscopic scale, as well as macro rheology to understand the material’s bulk mechanical properties. These two techniques complement each other to give us a more comprehensive idea of the material’s response to deformation,” she says.
“The goal of my project is to develop experiments to quantitatively characterize the time scale of the self-healing process of biological gels, especially on the microscopic scale,” Brunel explains. “To do so, I’m using the technique of active micro rheology with optical tweezers. Optical tweezers use a laser beam to trap micron-sized beads in a sample, and once a bead is trapped, it can be moved through the sample in a controlled manner. By dragging the bead around, we deform the material and then can see how the drag force on the bead changes over time as the material recovers. If the force required to move the bead through the material is lower than it was before the deformation, the material is still damaged, but if the resistance is the same, then the material has repaired itself. We can test these experiments on different time scales to get a more quantitative measurement of the self-healing process of these special biological gels.”
Brunel’s internship is supported in part by NSF’s Materials Research Science and Engineering Centers program [grant DMR-14-19807]. Participants in the Research Experience for Undergraduates, co-sponsored by the Materials Processing Center and the Center for Materials Science and Engineering, will present their results at a poster session during the last week of the program. The program runs from June 15, 2017, to August 5, 2017, on the MIT campus in Cambridge, Mass.
– Denis Paiste, Materials Processing Center
July 31, 2017
MIT researcher helps scientists and engineers hone their visual imagery.
|Felice Frankel, a research scientist in MIT’s Center for Materials Science and Engineering, has helped to produce images that just in the last few months have graced the covers of Nature, Nature Materials, and Environmental Science, among others. Image, Felice Frankel/Nature/Nature Materials|
Producing images powerful enough to be selected for the covers of major research journals is nothing new for Felice Frankel: She’s being doing it for decades with great success. But now, she’s extending that approach, using a growing arsenal of visual tools and techniques as she works with scientists and engineers to develop imagery that illustrates their concepts.
Frankel, a research scientist in MIT’s Center for Materials Science and Engineering, has helped to produce images that in the last few months have graced the covers of Nature, Nature Materials, and Environmental Science, among others. Some of her work is also featured in the exhibit “Images of Discovery: Communicating science through photography,” running at the MIT Museum through this August.
Frankel started her career in science and then turned to photographing architecture and landscapes, publishing a few books along the way. She started working with MIT scientists to improve their visual communications back in the ’90s. She’s been expanding her work ever since, both developing new ways of communicating ideas visually and teaching techniques for doing so.
Her latest work has involved combining a variety of photographic images into photo-illustrations that help to explain a process better than individual photos could. The latest journal covers have been examples of this approach. “I take pieces of photos I’ve already made and put them together as an illustration,” she says.
Read more at the MIT News Office.
David L. Chandler | MIT News Office
July 13, 2017
First “center of excellence” for new MIT.nano facility will focus on novel detectors and imaging systems.
|A discussion featured some of the speakers from the day-long SENSE.nano conference: [left to right] Juejun Hu, associate professor of materials science and engineering; Polina Anikeeva, associate professor of materials science and engineering; Max Shulaker, assistant professor of electrical engineering and computer science; Brian Anthony, principal research scientist in mechanical engineering and co-leader of SENSE.nano; and Vladimir Bulovic, associate dean for engineering and professor of emerging technology. Photo, Michael D. Spencer.|
In anticipation of the official opening of the new MIT.nano building — which will house some of the world’s leading facilities supporting research in nanoscience and nanotechnology — MIT officially launched a new “center of excellence” called SENSE.nano, which is dedicated to pushing the frontiers of research in sensing technologies.
Like the new building, which is slated to open a year from now, SENSE.nano is an endeavor that cuts across the divisions of departments, labs, and schools, to encompass research in areas including chemistry, physics, materials science, electronics, computer science, biology, mechanical engineering, and more. Faculty members from many of these areas spoke about their research during a daylong conference on May 25 that marked the official launch of the new center.
Introducing the event, MIT President L. Rafael Reif said that “[MIT.nano] will create opportunities for research and collaboration for more than half our current faculty, and 67 percent of those recently tenured. In fact, we expect that it will serve — and serve to inspire – more than 2,000 people across our campus, from all five MIT schools, and many more from beyond our walls.”
Read more at the MIT News Office.
David L. Chandler | MIT News Office
June 1, 2017
New center for development of high-tech fibers and fabrics opens headquarters, unveils two products ready for commercialization.
|Marty Ellis, of Inman Mills in South Carolina, checks a machine manufacturing fabric developed through AFFOA. Photo, courtesy of AFFOA.|
Just over a year after its funding award, a new center for the development and commercialization of advanced fabrics officially opened its headquarters June 19 in Cambridge, Massachusetts, and will be unveiling the first two advanced fabric products to be commercialized from the center’s work.
Advanced Functional Fabrics of America (AFFOA) is a public-private partnership, part of Manufacturing USA, that is working to develop and introduce U.S.-made high-tech fabrics that provide services such as health monitoring, communications, and dynamic design. In the process, AFFOA aims to facilitate economic growth through U.S. fiber and fabric manufacturing.
AFFOA’s national headquarters will open today, with an event featuring Under Secretary of Defense for Acquisition, Technology, and Logistics James MacStravic, U.S. Senator Elizabeth Warren, U.S. Rep. Niki Tsongas, U.S. Rep. Joe Kennedy, Massachusetts Governor Charlie Baker, New Balance CEO Robert DeMartini, MIT President L. Rafael Reif, and AFFOA CEO Yoel Fink. Sample versions of one of the center’s new products, a programmable backpack made of advanced fabric produced in North and South Carolina, will be distributed to attendees at the opening.
Read more at the MIT News Office.
David L. Chandler | MIT News Office
June 19, 2017
MPC-CMSE Summer Scholars tackling projects from magnetic thin films to catalysts for energy.
Summer Scholars co-sponsored by the Materials Processing Center and the Center for Materials Science and Engineering recently settled on their research projects and lab assignments. Summer Scholars faced a difficult decision to choose a lab after hearing enticing faculty presentations and lab tours.
Luke Soule found all the possible projects interesting but honed in on electrochemistry, choosing to work in the Prof. Yang Shao-Horn’s Electrochemical Energy Lab. During a tour of the lab, graduate student Karthik Akkiraju presented several research projects on the role of catalysts in lowering the energy needed to stimulate electrochemical reactions in energy devices. Akkiraju said Shao-Horn looks for students who are excited about the work and encourages students to be independent and to work together as a community. He emphasized the family-like atmosphere of the group. “At EEL, you never work alone,” Akkiraju says.
- Developing artificial mucus Developing artificial mucus
- Researching magnetic thin films Researching magnetic thin films
- Looking over 3D printed gear Looking over 3D printed gear
- Encouraging independence Encouraging independence
- Peeking inside a sputtering chamber Peeking inside a sputtering chamber
- Testing properties of biological gels Testing properties of biological gels
- Flow battery research Flow battery research
- Superconducting nanowire studies Superconducting nanowire studies
- Explaining laser bench Explaining laser bench
- Examining research samples Examining research samples
In Assistant Professor Luqiao Liu’s lab, electrical engineering and computer science graduate student Joseph T. Finley explained how he uses processes such as electron sputtering and ion milling to make magnetic thin films. The lab is developing new magnetically switchable materials for computer memory. Shortly after the lab tour, Summer Scholar Stephanie Bauman said, “I really like the one we just left, the anti-ferromagnetic, it seems to be mostly focused toward physics which is my major and more so than a lot of the other bio or chem projects.” Bauman chose to work in Liu’s lab this summer.
Alexandra Oliveira chose to work under Raymond A.  and Helen E. St. Laurent Career Development Professor of Chemical Engineering Fikile R. Brushett on redox flow batteries. ‘”Right now I’m working on the permeability of different microstructures for carbon electrodes and I’ll be attempting to electrograft molecules onto the electrodes to change their chemical properties for aqueous and non-aqueous flow batteries,” Oliveira says.
Summer Scholar Grace Noel chose to work in Charles and Hilda Roddey Career Development Professor in Chemical Engineering William A. Tisdale’s lab on a project to make and study metal halide perovskite nanoplatelets. These platelets, which are like flat quantum dots, are sometimes just over half a unit cell in thickness and their color can be adjusted by altering their composition.
Summer Scholar Richard B. [Ben] Canty is working in Associate Professor of Chemical Engineering Yuriy Román’s lab on a project to develop a catalyst for breaking down lignins in plant biomass into industrially useful chemicals like benzene. “I’m mixing in stuff in a tiny little batch reactor, putting it on a heater on a shelf, watching it so it doesn’t explode, centrifuging it and then running it on gas chromatographs and mass spectrometers,” Canty explains.
During the lab tour, NanoStructures Laboratory postdoc Reza Baghdadi explained how Prof. Karl Berggren aims to develop superconducting nanowires made of niobium nitride for reducing data processing energy consumption. The internship offers a chance to learn different fabrication skills, such as photolithography and electron beam lithography, thin film deposition and etching processes, with optical and electrical studies at liquid helium temperatures, about 4.2 kelvins. Summer Scholar Saleem Iqbal chose to work in the Berggren lab this summer.
AIM Photonics Academy interns were matched separately to their projects. Stuart Daudlin is working on “Statistical Modeling of Photonic Device Variations” with Duane Boning, the Clarence J. LeBel Professor of Electrical Engineering at MIT. Ryan Kosciolek is working on “Nonlinear Photonic Devices” with MIT Microphotonics Center Principal Research Scientist Anuradha [Anu] Agarwal. Summer Scholars attend regular weekly or bi-weekly lab group meetings. Larger groups have dedicated sub-groups as well that meet regularly.
The REU internships are supported in part by NSF’s Materials Research Science and Engineering Centers program [grant DMR-14-19807]. Participants will present their results at a poster session the last week of the program. The program runs from June 15, 2017, to August 5, 2017, on the MIT campus in Cambridge, Mass.
|Summer Scholar||Faculty Lab|
|Alejandro Aponte||Michael Cima|
|Stephanie Bauman||Luqiao Liu|
|Lucia Brunel||Gareth McKinley|
|Richard B. Canty||Yuriy Román|
|Stuart Daudlin||Duane Boning|
|Amrita Duggal||Paula Hammond|
|Kaila Holloway||Michael Strano|
|Saleem Iqbal||Karl Berggren|
|Ryan Kosciolek||Anuradha Agarwal|
|Gaetana Michelet||Katharina Ribbeck|
|Grace Noel||William Tisdale|
|Alexandra Oliveira||Fikile Brushett|
|Kirill Shmilovich||Alfredo Alexander-Katz|
|Luke Soule||Yang Shao-Horn|
- Written by Denis Paiste, Materials Processing Center
University of Massachusetts, Amherst, chemical engineering major Ashley L. Kaiser will return to MIT this coming fall as a graduate student in materials science and engineering. She will join Professor Brian Wardle's research group, where she worked during summer 2016 on strengthening aerospace nanocomposites with postdoc Itai Stein SM ’13, PhD ’16. Kaiser, who was accepted to five graduate schools, was one of six to win UMass Amherst’s Rising Researcher award. Her Commonwealth Honors College thesis project focused on “Low-Temperature Graphene Growth by Plasma-Enhanced Chemical Vapor Deposition.”
- Alexandra T. Barth, 2016 Summer Scholar Alexandra T. Barth, 2016 Summer Scholar
- Ashley L. Kaiser, 2016 Summer Scholar Ashley L. Kaiser, 2016 Summer Scholar
- Grant Smith, 2016 Summer Scholar Grant Smith, 2016 Summer Scholar
- Justin Cheng, 2016 Summer Scholar Justin Cheng, 2016 Summer Scholar
Alexandra T. Barth received a “Most Outstanding Senior” award from Florida State University, where she was part of the Honors Program. Barth will pursue a PhD in Chemistry at the California Institute of Technology. She will start as a research assistant in the fall under Dr. Theo Agapie, synthesizing metal oxide clusters and arene-supported complexes that act as chemical catalysts. “My internship last summer was vital in introducing me and providing a foundational knowledge of catalyst research, which was very different from the undergraduate research I had conducted at my own institution, and I am confident that the relationship I established with my MIT research advisor Dr. Román enabled this opportunity,” Barth says.
Grant Smith, will begin doctoral studies at the University of Chicago Institute for Molecular Engineering as an IME Fellow working on quantum information systems and materials. Smith worked last summer to establish parameters for making ferromagnetic thin films in the Luqiao Liu lab.
Justin Cheng will enroll this fall in the University of Minnesota Twin Cities Chemical Engineering and Materials Science Ph.D. program. During summer 2016, Cheng worked in Professor of Electrical Engineering Karl K. Berggren’s Quantum Nanostructures and Nanofabrication Group to develop specialized techniques for patterning gold on silicon.
Allanore lab develops electrically-driven process to separate commercially important metals from sulfide minerals in one step without harmful byproducts.
|MIT postdoc Sulata K. Sahu [left] and graduate student Brian Chmielowiec hold a sample of nearly pure copper deposited on an iron electrode after extraction through chemical electrolysis from an electrolyte composition of 70 percent barium sulfide and 30 percent copper sulfide. Photo, Denis Paiste, Materials Processing Center.|
MIT researchers have identified the proper temperature and chemical mixture to selectively separate pure copper and other metallic trace elements from sulfur-based minerals using molten electrolysis. This one-step, environmentally friendly process simplifies metal production and eliminates the toxic byproducts such as sulfur dioxide.
Postdoc Sulata K. Sahu and Ph.D. student Brian J. Chmielowiec SB, ’12 decomposed sulfur-rich minerals into pure sulfur and extracted three different metals at very high purity – copper, molybdenum and rhenium. They also quantified the amount of energy needed to run the extraction process.
An electrolysis cell is a closed circuit, like a battery, but instead of producing electrical energy, it consumes electrical energy to break apart compounds into their elements, for example, splitting water into hydrogen and oxygen. Such electrolytic processes are the primary method of aluminum production and are used as the final step to remove impurities in copper production. Contrary to aluminum, however, there are no direct electrolytic decomposition processes for copper-containing sulfide minerals to produce liquid copper.
The MIT researchers found a promising method of forming liquid copper metal and sulfur gas in their cell from an electrolyte composed of barium sulfide, lanthanum sulfide, and copper sulfide, which yields greater than 99.9 percent pure copper. This purity is equivalent to the best current copper production methods. Their results are published in an Electrochimica Acta paper with senior author Antoine Allanore, Assistant Professor of Metallurgy. [Allanore becomes Associate Professor as of July 1, 2017.]
“It is a one-step process, directly just decompose the sulfide to copper and sulfur. Other previous methods are multiple steps,” Sahu explains. “By adopting this process, we are aiming to reduce the cost.”
Copper is in increasing demand for electric vehicles, solar energy, consumer electronics and other energy efficiency targets. Most current copper extraction processes burn sulfide minerals in air, which produces sulfur dioxide, a harmful air pollutant that has to be captured and reprocessed, but the new method produces elemental sulfur, which can be safely reused, for example, in fertilizers. The researchers also used electrolysis to produce rhenium and molybdenum, which are often found in copper sulfides at very small levels.
The new work builds on a 2016 Journal of The Electrochemical Society paper offering proof of electrolytic extraction of copper authored by Samira Sokhanvaran, Sang-Kwon Lee, Guillaume Lambotte, and Allanore. They showed that addition of barium sulfide to a copper sulfide melt suppressed copper sulfide’s electrical conductivity enough to extract a small amount of pure copper from the high-temperature electrochemical cell operating at 1,105 degrees Celsius [2,021 Fahrenheit]. Sokhanvaran is now a research scientist at Natural Resources Canada-Canmet Mining; Lee is a senior researcher at Korea Atomic Energy Research Institute; and Lambotte is now a senior research engineer at Boston Electrometallurgical Corp.
“This paper was the first one to show that you can use a mixture where presumably electronic conductivity dominates conduction, but there is not actually 100 percent. There is a tiny fraction that is ionic, which is good enough to make copper,” Allanore explains.
“The new paper shows that we can go further than that and almost make it fully ionic, that is reduce the share of electronic conductivity and therefore increase the efficiency to make metal,” Allanore says.
|A new penny, at left, contrasts with samples of nearly pure copper deposited on an iron electrode after extraction through an electrochemical process from an electrolyte composed of 70 percent barium sulfide and 30 percent copper sulfide. Photo, Denis Paiste, Materials Processing Center.|
These sulfide minerals are compounds where the metal and the sulfur elements share electrons. In their molten state, copper ions are missing one electron, giving them a positive charge, while sulfur ions are carrying two extra electrons, giving them a negative charge. The desired reaction in an electrolysis cell is to form elemental atoms, by adding electrons to metals such as copper, and taking away electrons from sulfur. This happens when extra electrons are introduced to the system by the applied voltage. The metal ions are reacting at the cathode [a negatively charged electrode] where they gain electrons [reduction] while the negatively charged sulfur ions are reacting at the anode [a positively charged electrode], where they give up electrons [oxidation].
In a cell that used only copper sulfide, for example, because of its high electronic conductivity, the extra electrons would simply flow through the electrolyte without interacting with the individual ions of copper and sulfur at the electrodes and no separation would occur. The Allanore group researchers successfully identified other sulfide compounds that, when added to copper sulfide, change the behavior of the melt so that the ions, rather than electrons, become the primary charge carriers through the system and thus enable the desired chemical reactions. Technically speaking, the additives raise the bandgap of the copper sulfide so it is no longer electronically conductive, Chmielowiec explains. The fraction of the electrons engaging in the oxidation and reduction reactions, measured as a percentage of the total current, that is the total electron flow, in the cell, is called its faradaic efficiency.
The new work doubles the efficiency for electrolytic extraction of copper reported in the first paper, which was 28 percent with an electrolyte where only barium sulfide added to the copper sulfide, to 59 percent in the second paper with both lanthanum sulfide and barium sulfide added to the copper sulfide.
“Demonstrating that we can perform faradaic reactions in a liquid metal sulfide is novel and can open the door to study many different systems,” Chmielowiec says. “It works for more than just copper. We were able to make rhenium, and we were able to make molybdenum.” Rhenium and molybdenum are industrially important metals finding use in jet airplane engines, for example. The Allanore laboratory also used molten electrolysis to produce zinc, tin and silver, but lead, nickel and other metals are possible, he suggests.
The amount of energy required to run the separation process in an electrolysis cell is proportional to the faradaic efficiency and the cell voltage. For water, which was one of the first compounds to be separated by electrolysis, the minimum cell voltage, or decomposition energy, is 1.23 volts. Sahu and Chmielowiec identified the cell voltages in their cell as 0.06 volts for rhenium sulfide, 0.33 volts for molybdenum sulfide and 0.45 volts for copper sulfide. “For most of our reactions, we apply 0.5 or 0.6 volts, so that the three sulfides are together reduced to metallic, rhenium, molybdenum and copper,” Sahu explains. At the cell operating temperature and at an applied potential of 0.5 to 0.6 volts, the system prefers to decompose those metals because the energy required to decompose both lanthanum sulfide [about 1.7 volts] and barium sulfide [about 1.9 volts] is comparatively much higher. Separate experiments also proved the ability to selectively reduce rhenium or molybdenum without reducing copper, based on their differing decomposition energies.
Important strategic and commodity metals including, copper, zinc, lead, rhenium and molybdenum are typically found in sulfide ores and less commonly in oxide-based ores, as is the case for aluminum. “What’s typically done is you burn those in air to remove the sulfur, but by doing that you make SO2 [sulfur dioxide], and nobody is allowed to release that directly to air, so they have to capture it somehow. There are a lot of capital costs associated with capturing SO2 and converting it to sulfuric acid,” Chmielowiec explains.
|The desired reaction in an electrolysis cell is to decompose a chemical compound into its constituent elements [shown here as S for sulfur and M for metals], by adding electrons to metallic ions such as copper, and removing electrons from sulfur ions. This happens when extra electrons [designated e–] are added through an applied voltage. MIT researchers have identified the proper temperature and chemical mixture to separate copper, rhenium and molybdenum from sulfur-based minerals using molten electrolysis. Illustration, Brian J. Chmielowiec.|
The closest industrial process to the electrolytic copper extraction they hope to see is aluminum production by an electrolytic process known as Hall-Héroult process, which produces a pool of molten aluminum metal that can be continuously tapped. “The ideal is to run a continuous process,” Chmielowiec says. “So, in our case, you would maintain a constant level of liquid copper and then periodically tap that out of the electrolysis cell. A lot of engineering has gone into that for the aluminum industry, so we would hopefully piggyback off of that.”
Sahu and Chmielowiec conducted their experiments at 1,227 degrees Celsius [2,240 Fahrenheit], about 150 degrees Celsius above the melting point of copper. It is the temperature commonly used in industry for copper extraction.
Aluminum electrolysis systems run at 95 percent faradaic efficiency, so there is room for improvement from the researchers’ reported 59 percent efficiency. To improve their cell efficiency, Sahu says, they may need to modify the cell design to recover a larger amount of liquid copper. The electrolyte can also be further tuned, adding sulfides other than barium sulfide and lanthanum sulfide. “There is no one single solution that will let us do that. It will be an optimization to move it up to larger scale,” Chmielowiec says. That work continues.
Sahu, 34, received her Ph.D. in chemistry from the University of Madras, in India. Chmielowiec, 27, a second-year doctoral student and a Salapatas Fellow in materials science and engineering, received his S.B. in chemical engineering at MIT in 2012 and an M.S. in chemical engineering from California Institute of Technology in 2014.
The work fits into the Allanore Group’s work on high-temperature molten materials, including recent breakthroughs in developing new formulas to predict semiconductivity in molten compounds and demonstrating a molten thermoelectric cell to produce electricity from industrial waste heat. The Allanore Group is seeking a patent on certain aspects of the extraction process.
Novel and significant work
“Using intelligent design of the process chemistry, these researchers have developed a very novel route for producing copper,” says Rohan Akolkar, the F. Alex Nason Associate Professor of Chemical and Biomolecular Engineering at Case Western Reserve University, who was not involved in this work. “The researchers have engineered a process that has many of the key ingredients – it's a cleaner, scalable and simpler one-step process for producing copper from sulfide ore.”
“Technologically, the authors appreciate the need to make the process more efficient while preserving the intrinsic purity of the copper produced,” says Akolkar, who visited the Allanore lab late last year. “If the technology is developed further and its techno-economics look favorable, then it may provide a potential pathway for simpler and cleaner production of copper metal, which is important to many applications.” Akolkar notes that “the quality of this work is excellent. The Allanore research group at MIT is at the forefront when it comes to advancing molten salt electrolysis research.”
University of Rochester Professor of Chemical Engineering Jacob Jorné says that “Current extraction processes involve multiple steps and require high capital investment, thus costly improvements are prohibited. Direct electrolysis of the metal sulfide ores is also advantageous as it eliminates the formation of sulfur dioxide, an acid rain pollutant. “
“The electrochemistry and thermodynamics in molten salts are quite different than in aqueous [water-based] systems and the research of Allanore and his group demonstrates that a lot of good chemistry has been ignored in the past due to our slavish devotion to water,” Jorné suggests. “Direct electrolysis of metal ores opens the way to a metallurgical renaissance where new discoveries and processes can be implemented and can modernize the aging extraction industry and improve its energy efficiency. The new approach can be applied to other metals of high strategic importance such as the rare earth metals.”
This work was supported by Norco Conservation and the Office of Naval Research [contract N00014-12-1-0521].
– Denis Paiste, Materials Processing Center
|Finding the Right Chemical Combination for Copper Extraction|
|Liquid tin-sulfur compound shows thermoelectric potential|
|Predicting high-temperature, liquid electronic properties|