Own your own data

A new system would allow individuals to pick and choose what data to share with websites and mobile apps.

Cellphone metadata has been in the news quite a bit lately, but the National Security Agency isn’t the only organization that collects information about people’s online behavior. Newly downloaded cellphone apps routinely ask to access your location information, your address book, or other apps, and of course, websites like Amazon or Netflix track your browsing history in the interest of making personalized recommendations.

At the same time, a host of recent studies have demonstrated that it’s shockingly easy to identify unnamed individuals in supposedly “anonymized” data sets, even ones containing millions of records. So, if we want the benefits of data mining — like personalized recommendations or localized services — how can we protect our privacy?

In the latest issue of PLOS One, MIT researchers offer one possible answer. Their prototype system, openPDS — short for personal data store — stores data from your digital devices in a single location that you specify: It could be an encrypted server in the cloud, but it could also be a computer in a locked box under your desk. Any cellphone app, online service, or big-data research team that wants to use your data has to query your data store, which returns only as much information as is required.

Sharing code, not data

“The example I like to use is personalized music,” says Yves-Alexandre de Montjoye, a graduate student in media arts and sciences and first author on the new paper. “Pandora, for example, comes down to this thing that they call the music genome, which contains a summary of your musical tastes. To recommend a song, all you need is the last 10 songs you listened to — just to make sure you don’t keep recommending the same one again — and this music genome. You don’t need the list of all the songs you’ve been listening to.”

With openPDS, de Montjoye says, “You share code; you don’t share data. Instead of you sending data to Pandora, for Pandora to define what your musical preferences are, it’s Pandora sending a piece of code to you for you to define your musical preferences and send it back to them.”

De Montjoye is joined on the paper by his thesis advisor, Alex “Sandy” Pentland, the Toshiba Professor of Media Arts and Sciences; Erez Shmueli, a postdoc in Pentland’s group; and Samuel Wang, a software engineer at Foursquare who was a graduate student in the Department of Electrical Engineering and Computer Science when the research was done.

After an initial deployment involving 21 people who used openPDS to regulate access to their medical records, the researchers are now testing the system with several telecommunications companies in Italy and Denmark. Although openPDS can, in principle, run on any machine of the user’s choosing, in the trials, data is being stored in the cloud.

Meaningful permissions

One of the benefits of openPDS, de Montjoye says, is that it requires applications to specify what information they need and how it will be used. Today, he says, “when you install an application, it tells you ‘this application has access to your fine-grained GPS location,’ or it ‘has access to your SD card.’ You as a user have absolutely no way of knowing what that means. The permissions don’t tell you anything.”

In fact, applications frequently collect much more data than they really need. Service providers and application developers don’t always know in advance what data will prove most useful, so they store as much as they can against the possibility that they may want it later. It could, for instance, turn out that for some music listeners, album cover art turns out to be a better predictor of what songs they’ll like than anything captured by Pandora’s music genome.

OpenPDS preserves all that potentially useful data, but in a repository controlled by the end user, not the application developer or service provider. A developer who discovers that a previously unused bit of information is useful must request access to it from the user. If the request seems unnecessarily invasive, the user can simply deny it.

Of course, a nefarious developer could try to game the system, constructing requests that elicit more information than the user intends to disclose. A navigation application might, for instance, be authorized to identify the subway stop or parking garage nearest the user. But it shouldn’t need both pieces of information at once, and by requesting them, it could infer more detailed location information than the user wishes to reveal.

Creating safeguards against such information leaks will have to be done on a case-by-case, application-by-application basis, de Montjoye acknowledges, and at least initially, the full implications of some query combinations may not be obvious. But “even if it’s not 100 percent safe, it’s still a huge improvement over the current state,” he says. “If we manage to get people to have access to most of their data, and if we can get the overall state of the art to move from anonymization to interactive systems, that would be such a huge win.”

“OpenPDS is one of the key enabling technologies for the digital society, because it allows users to control their data and at the same time open up its potential both at the economic level and at the level of society,” says Dirk Helbing, a professor of sociology at ETH Zurich. “I don’t see another way of making big data compatible with constitutional rights and human rights.”

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Drone lighting

Autonomous vehicles could automatically assume the right positions for photographic lighting.

Lighting is crucial to the art of photography. But lights are cumbersome and time-consuming to set up, and outside the studio, it can be prohibitively difficult to position them where, ideally, they ought to go.

Researchers at MIT and Cornell University hope to change that by providing photographers with squadrons of small, light-equipped autonomous robots that automatically assume the positions necessary to produce lighting effects specified through a simple, intuitive, camera-mounted interface.

At the International Symposium on Computational Aesthetics in Graphics, Visualization, and Imaging in August, they take the first step toward realizing this vision, presenting a prototype system that uses an autonomous helicopter to produce a difficult effect called “rim lighting,” in which only the edge of the photographer’s subject is strongly lit.

According to Manohar Srikanth, who worked on the system as a graduate student and postdoc at MIT and is now a senior researcher at Nokia, he and his coauthors —MIT professor of computer science and engineering Frédo Durand and Cornell’s Kavita Bala, who also did her PhD at MIT — chose rim lighting for their initial experiments precisely because it’s a difficult effect.

“It’s very sensitive to the position of the light,” Srikanth says. “If you move the light, say, by a foot, your appearance changes dramatically.”

Intuitive control

With the new system, the photographer indicates the direction from which the rim light should come, and the miniature helicopter flies to that side of the subject. The photographer then specifies the width of the rim as a percentage of its initial value, repeating that process until the desired effect is achieved.

Thereafter, the robot automatically maintains the specified rim width. “If somebody is facing you, the rim you would see is on the edge of the shoulder, but if the subject turns sideways, so that he’s looking 90 degrees away from you, then he’s exposing his chest to the light, which means that you’ll see a much thicker rim light,” Srikanth says. “So in order to compensate for the change in the body, the light has to change its position quite dramatically.”

In the same way, Srikanth says, the system can compensate for the photographer’s movements. In both cases, the camera itself supplies the control signal. Roughly 20 times a second, the camera produces an image that is not stored on its own memory card but transmitted to a computer running the researchers’ control algorithm. The algorithm evaluates the rim width and adjusts the robot’s position accordingly.

“The challenge was the manipulation of the very difficult dynamics of the UAV [unmanned aerial vehicle] and the feedback from the lighting estimation,” Durand says. “That’s where we put a lot of our efforts, to make sure that the control of the drone could work at the very high speed that’s needed just to keep the thing flying and deal with the information from the lidar [the UAV’s laser rangefinder] and the rim-lighting estimation.”

Quick study

As Srikanth explains, that required some algorithmic streamlining. “When we first started looking at it, we thought we’d come up with a very fancy algorithm that looks at the whole silhouette of the subject and tries to figure out the morphological properties, the curve of the edge, and so on and so forth, but it turns out that those calculations are really time-consuming,” Srikanth says.

Instead, the algorithm simply looks for the most dramatic gradations in light intensity across the whole image and measures their width. With a rim-lit subject, most of those measurements will congregate around the same value, which the algorithm takes to be the width of the rim.

In experiments, this quick approximation was able to keep up with the motions of both the subject and the photographer while maintaining a consistent rim width.

The researchers tested their prototype in a motion-capture studio, which uses a bank of high-speed cameras to measure the position of specially designed light-reflecting tags with millimeter accuracy; several such tags were affixed to the helicopter.

But, Srikanth explains, the purpose of the tests was to evaluate the control algorithm, which performed well. Algorithms that gauge robots’ location based only on measurements from onboard sensors are a major area of research in robotics, and the new system could work with any of them. Even rim lighting, Srikanth says, doesn’t require the millimeter accuracy of the motion-capture studio. “We only need a resolution of 2 or 3 centimeters,” he says.

“Rim lighting is a particularly interesting effect, because you want to precisely position the lighting to bring out silhouettes,” says Ravi Ramamoorthi, a professor of computer science and engineering at the the University of California, San Diego. “Other effects are in some sense easier — one doesn't need as precise positioning for frontal lighting. So the technique would probably generalize to other light effects. But at the same time, as-precise control and manipulation may not be needed. Manual static positioning might be adequate.”

“Clearly, taking the UAV system out of the lab and into the real world, and making it robust enough to be practical is a challenge,” Ramamoorthi adds, “but also something that should be doable given the rapid advancement of all of these technologies.”

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Seeing the inner workings of the brain made easier

Karl Deisseroth, MD, PhD, and his team have improved on their original technique for peering into the intact brain.

Last year, Karl Deisseroth, MD, PhD, professor of bioengineering and of psychiatry and behavioral sciences, announced a new way of peering into a disembodied brain that provided spectacular fly-through views of its inner connections. Since then, laboratories around the world have begun using the technique, called CLARITY, with some success to better understand the brain’s wiring.

But two technological hurdles have kept the technique from being more broadly adopted. The first was the problem of removing fat from the brain without damaging the organ’s complex wiring. Second, the most commonly available microscopy methods were not designed to image the whole transparent brain.

“There have been a number of remarkable results described using CLARITY,” Deisseroth said, “but we needed to address these two distinct challenges to make the technology easier to use.”

In a Nature Protocols paper published June 19, Deisseroth and his team present solutions to both of those challenges. “These transform CLARITY, making the overall process much easier and the data collection much faster,” he said. Deisseroth, who is senior author of the paper, anticipates that even more scientists will now be able to take advantage of the technique to better understand the brain at a fundamental level, and also to probe the origins of brain diseases. The paper’s lead author is postdoctoral scholar Raju Tomer, PhD.

The study may be the first to have been published with support of the White House BRAIN Initiative, announced last year with the ambitious goal of mapping the brain’s trillions of nerve connections and understanding how signals zip through those interconnected cells to control our thoughts, memories, movement and everything else that makes us.

“This work shares the spirit of the BRAIN Initiative goal of building new technologies to understand the brain — including the human brain,” said Deisseroth, who is also a Stanford Bio-X affiliated faculty member.

Eliminating fat

When you look at the brain, what you see is the fatty outer covering of the nerve cells within, which blocks microscopes from taking images of the intricate connections between deep brain cells. The idea behind CLARITY was to eliminate that fatty covering while keeping the brain intact, complete with all its intricate inner wiring.

The way Deisseroth and his team eliminated the fat was to build a gel within the intact brain that held all the structures and proteins in place. They then used an electric field to pull out the fat layer that had been dissolved in an electrically charged detergent, leaving behind all the brain’s structures embedded in the firm water-based gel, or hydrogel. This is called electrophoretic CLARITY.

The electric field aspect was a challenge for some labs. “About half the people who tried it got it working right away,” Deisseroth said, “but others had problems with the voltage damaging tissue.” Deisseroth said that this kind of challenge is normal when introducing new technologies. When he first introduced optogenetics, which allows scientists to control individual nerves using light, a similar proportion of labs were not initially set up to easily implement the new technology, and ran into challenges.

To help expand the use of CLARITY, the team devised an alternate way of pulling out the fat from the hydrogel-embedded brain — a technique they call passive CLARITY. It takes a little longer, but still removes all the fat, is much easier and does not pose a risk of damaging the neuronal structures. “Electrophoretic CLARITY is important for cases where speed is critical, and for some tissues,” said Deisseroth, who is also the D.H. Chen Professor. “But passive CLARITY is a crucial advance for the community, especially for neuroscience.” Passive CLARITY requires nothing more than some chemicals, a warm bath and time.

Many groups have begun to apply CLARITY to probe brains donated from people who had diseases like epilepsy or autism, which might have left clues in the brain to help scientists understand and eventually treat the disease. But scientists, including Deisseroth, had been wary of trying electrophoretic CLARITY on these valuable clinical samples with even a very low risk of damage. “It’s a rare and precious donated sample; you don’t want to have a chance of damage or error,” Deisseroth said. “Now the risk issue is addressed, and on top of that you can get the data very rapidly.”

Fast CLARITY imaging in color

The second advance had to do with the rapidity of data collection. In studying any cells, scientists often make use of probes that will go into the cell or tissue, latch onto a particular molecule, then glow green, blue, yellow or other colors in response to particular wavelengths of light. This is what produces the colorful cellular images that are so common in biology research. Using CLARITY, these colorful structures become visible throughout the entire brain, since no fat remains to block the light.

This work shares the spirit of the BRAIN Initiative goal of building new technologies to understand the brain — including the human brain.

But here’s the hitch: Those probes stop working, or get bleached, after they’ve been exposed to too much light. That’s fine if a scientist is just taking a picture of a small cellular structure, which takes little time. But to get a high-resolution image of an entire brain, the whole tissue is bathed in light throughout the time it takes to image it point by point. This approach bleaches out the probes before the entire brain can be imaged at high resolution.

The second advance of the new paper addresses this issue, making it easier to image the entire brain without bleaching the probes. “We can now scan an entire plane at one time instead of a point,” Deisseroth said. “That buys you a couple orders of magnitude of time, and also efficiently delivers light only to where the imaging is happening.” The technique is called light-sheet microscopy and has been around for a while, but previously didn’t have high enough resolution to see the fine details of cellular structures. “We advanced traditional light-sheet microscopy for CLARITY, and can now see fine wiring structures deep within an intact adult brain,” Deisseroth said. His lab built their own microscope, but the procedures are described in the paper, and the key components are commercially available. Additionally, Deisseroth’s lab provides free training courses in CLARITY, modeled after his optogenetics courses, to help disseminate the techniques.

Other Stanford co-authors of the paper are postdoctoral scholar Li Ye, PhD, and graduate student Brian Hsueh.

The research was supported by Defense Advance Research Projects Agency, the National Institute of Mental Health, the National Science Foundation, the National Institute on Drug Abuse, the Simons Foundation and the Wiegers Family Fund.

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Worrisome growth pattern

Researchers connect earlier spring to climate change

Every spring, as the weather warms, trees up and down the East Coast explode in a display of bright green life as leaves fill their branches, and every fall, the same leaves provide one of nature’s great color displays of vivid yellow, orange, and red.

Thanks to climate change, the timing of those events has shifted over the last two decades, Harvard scientists say.

Andrew Richardson, an associate professor of organismic and evolutionary biology, and research associate Trevor Keenan worked with colleagues from seven different institutions on a study that found that forests throughout the eastern United States are showing signs of spring growth dramatically earlier, and that the growing season in some areas extends further into the fall. The expanded growing season, they say, has enabled forests to store as much as 26 million metric tons more CO2 than before. The work is described in a June 1 paper published in Nature Climate Change.

“What we find in this paper is an increase in the growing season of forests in the eastern U.S. due to recent climate change,” Keenan said. “This has been beneficial for forests in the past, but we do not expect the response to continue unchecked in the future. It must also be kept in mind that this positive effect of warming is but one amid a barrage of detrimental impacts of climate change on the Earth’s ecosystems.”

The fact that forests can store more carbon is a good thing, but both Keenan and Richardson warned that it’s far from so good as to cancel the potential devastation of climate change.

“Yes, 26 million metric tons is a lot of carbon, but it’s still small when compared to fossil fuel emissions,” Richardson said.

“And climate change isn’t just about warmer temperatures. It’s also about changes in precipitation patterns … so in the future, an earlier spring might not help forests take up more carbon if they end up running out of water in mid-summer.”

The research integrated information from three sources: satellite imagery, on-the-ground observations, and instrument towers.

By collecting data across different scales, Keenan was able to capture both a regional picture of the eastern forest — which stretches along the seaboard from Maine to Georgia, and as far inland as Wisconsin — and a more granular measurement of individual sites.

Using satellite data, Keenan tracked when forests across the region began to green in the spring, and when leaves began to turn in the fall. Ground observations made every three to seven days at the Harvard Forest in Petersham and at a long-term research site in New Hampshire provided information about the state of buds, leaves, and branches.

When combined with records from instrument towers, the data sets allowed the researchers to paint a richly detailed picture that shows spring starting earlier, and a growing season lasting longer than at any point in the past two decades.

“Basically, we showed that there are three different ways of looking at this, and they all show the same result — spring is getting earlier,” Richardson said. “When you look at the patterns across both space and time, and year-to-year at individual sites, and when you look across different species, the same patterns hold up … that gives us confidence that there’s something going on.”

Another important result, Richardson said, was the discovery of a significant source of error in existing computer models on how forest ecosystems work. It turns out that these models don’t properly reflect how spring and autumn temperatures control the start and end of the growing season.

“What that means is if you run these models forward 100 years, they won’t be accurate,” he said. “This shows an opportunity to improve the models and how they simulate how forests will work under future climate scenarios.”

The real power of the findings, however, may be in helping make the effects of climate change more tangible to the public, the researchers said.

“If you tell people the leaves are going to start coming out in mid-April, and it used to be in early May, that’s something people can relate to more easily than describing temperature-change records,” Richardson said. “People are just inherently fascinated by the passing of the seasons and weather, and how those two are connected.”

Improving stem cells’ regenerative potential

Harvard research team pursues techniques to master an elusive therapy

Stem cell scientists scored what at first appeared an easy win for regenerative medicine when they discovered mesenchymal stem cellsseveral decades ago. These cells, found in bone marrow, can give rise to fat, bone, and muscle tissue, and have been used in hundreds of clinical trials for tissue repair. Unfortunately, the results of these trials have been underwhelming. One problem is that these stem cells don’t stick around in the body long enough to benefit patients.

But Harvard Stem Cell Institute (HSCI) scientists at Boston Children’s Hospitalaren’t ready to give up. A research team led by Juan Melero-Martin and surgical research fellow Ruei-Zeng Lin recently found that transplanting mesenchymal stem cells along with blood-vessel-forming cells naturally found in circulation improves results. This co-transplantation keeps the mesenchymal stem cells alive longer in mice after engraftment — up to a few weeks compared with hours without co-transplantation.

This improved survival gives the mesenchymal stem cells sufficient time to display their full regenerative potential, creating new bone or fat tissue in recipient mouse bodies. The finding was published in the Proceedings of the National Academy of Sciences (PNAS).

“We are losing mesenchymal stem cells very rapidly when we transplant them into the body, in part because we are not giving them what they need,” said Melero-Martin, an HSCI-affiliated faculty member and an assistant professor of surgery at Boston Children’s Hospital, for Harvard Medical School.

“In the body, these cells sit very close to the capillaries, constantly receiving signals from them, and even though this communication is broken when we isolate mesenchymal stem cells in a laboratory dish, they seem to be OK because we have learned how to feed them,” he said. “But when you put the mesenchymal stem cells back into the body, there is a period of time when they will not have this proximity to capillary cells, and they start to die. So including these blood-vessel-forming cells from the very beginning of a transplantation made a major difference.”

Melero-Martin’s research has immediate implications, as current mesenchymal clinical trials don’t follow a co-transplantation procedure. He is already collaborating with surgical colleagues at Boston Children’s Hospital to see if his discovery can help improve fat and bone grafts. However, giving patients two types of cells, as opposed to one, would require more time and experiments to determine safety and efficacy. Melero-Martin is seeking to identify the specific signals mesenchymal stem cells receive from the blood-vessel-forming cells in order to be able to mimic the signals without the cells themselves.

“Even though mesenchymal stem cells have been around for a while, I think there is still a lack of fundamental knowledge about communication between them and other cells in the body,” he said. “My lab is interested in going even beyond what we found to try to understand whether these cell-cell signals are different in each tissue of the body, and to learn how to educate both blood-vessel-forming and mesenchymal stem cells to coordinate tissue-specific regenerative responses.”

Other HSCI researchers are studying mesenchymal stem cells as bioengineering tools to deliver therapeutics, which is possible because of the cell type’s unique ability to not trigger an immune response. Jeffrey Karp at Brigham and Women’s Hospital has developed several methods to turn these cells into drug-delivery vehicles, so that after transplantation they can, for example, hone in on swollen tissue and secrete anti-inflammatory compounds. And Khalid Shah at Massachusetts General Hospital has designed a gel that holds mesenchymal stem cells in place so that they can expose brain tumors to cancer-killing herpes viruses.

“A lot of these applications have no real direct link with mesenchymal stem cells’ supposed progenitor cell function,” Melero-Martin said. “In our study, we went back to the collective ambition to use these cells as a way to regenerate tissues, and we are not in a position to say how that affects other uses that people are proposing.”

The work was supported by the National Institutes of Health.

Vasectomy may increase risk of aggressive prostate cancer

Study linking the two is largest and most comprehensive to date

Vasectomy is associated with a small increased risk of prostate cancer, and a stronger risk for advanced or lethal prostate cancer, according to a new study from Harvard School of Public Health (HSPH). The researchers found that the association remained even among men who received regular prostate-specific antigen (PSA) screening, suggesting the increased risk of lethal cancer cannot be explained by diagnostic bias. It is the largest and most comprehensive study to date to look at the link between vasectomy and prostate cancer.

The study appeared online July 7 in Journal of Clinical Oncology.

The results showed a 10 percent increased risk of prostate cancer overall in men who had a vasectomy. Vasectomy was not significantly associated with risk of low-grade cancer; however, it was associated with stronger risks of advanced and lethal prostate cancer, by an additional 20 percent and 19 percent respectively. Among men who received regular PSA screening, the relative increase in risk of lethal prostate cancer was 56 percent. The effect appeared to be stronger among men who had a vasectomy at a younger age.

“This study follows our initial publication on vasectomy and prostate cancer in 1993, with 19 additional years of follow-up and tenfold greater number of cases. The results support the hypothesis that vasectomy is associated with an increased risk of advanced or lethal prostate cancer,” said co-author Lorelei Mucci, associate professor of epidemiology at HSPH.

Vasectomy is a common form of contraception in the United States, with about 15 percent of men undergo the procedure. Prostate cancer is the second-leading cause of cancer death among American men, so identifying risk factors for lethal prostate cancer is important for public health.

The researchers analyzed data from the Health Professionals Follow-Up Study, which followed 49,405 American men for up to 24 years between 1986 and 2010. During that time, 6,023 cases of prostate cancer were diagnosed, including 811 lethal cases. One in four of the men in this study reported having a vasectomy.

Prior work on this topic raised concerns that the positive associations could be linked to bias. However, in the present study, the researchers had access to diverse information and could rule out potential biases, including the possibilities that men who have vasectomies seek more medical care in general or have higher rates of PSA screening, or that the association was due driven by differences in sex hormone levels, sexually transmitted infections, or cancer treatment.

Among the men in this study, 16 in 1,000 developed lethal prostate cancer during 24 years of follow-up. Although the relative increase in the risk associated with vasectomy was significant, this translates to a comparatively small increase in absolute difference in the risk of lethal prostate cancer, the researchers said. “The decision to opt for a vasectomy as a form of birth control is a highly personal one and a man should discuss the risks and benefits with his physician,” said co-author Kathryn Wilson, research associate in the Department of Epidemiology at HSPH.

Researchers led by Stanford engineer figure out how to make more efficient fuel cells

Using high-brilliance X-rays, researchers track the process that fuel cells use to produce electricity, knowledge that will help make large-scale alternative energy power systems more practical and reliable.

Solar power and other sources of renewable energy can help combat global warming but they have a drawback: they don't produce energy as predictably as plants powered by oil, coal or natural gas. Solar panels only produce electricity when the sun is shining, and wind turbines are only productive when the wind is brisk.

Ideally, alternative energy sources would be complemented with massive systems to store and dispense power – think batteries on steroids. Reversible fuel cells have been envisioned as one such storage solution.

  Fuel cells use oxygen and hydrogen as fuel to create electricity; if the process were run in reverse, the fuel cells could be used to store electricity, as well.

"You can use the electricity from wind or solar to split water into hydrogen and oxygen in a fuel cell operating in reverse," said William Chueh, an assistant professor of materials science and engineering at Stanford and a member of the Stanford Institute of Materials and Energy Sciences at SLAC National Accelerator Laboratory.  "The hydrogen can be stored, and used later in the fuel cell to generate electricity at night or when the wind isn't blowing."

But like the renewable energy sources they seek to complement, fuel cells also have a drawback: the chemical reactions that cleave water into hydrogen and oxygen or join them back together into water are not fully understood – at least not to the degree of precision required to make utility-grade storage systems practical.

Now Chueh, working with researchers at SLAC, Lawrence Berkeley National Laboratory and Sandia National Laboratories, has studied the chemical reactions in a fuel cell in a new and important way.

In a paper published today in Nature Communications, Chueh and his team describe how they observed the hydrogen-oxygen reaction in a specific type of high-efficiency solid-oxide fuel cell and took atomic-scale "snapshots" of this process using a particle accelerator known as a synchrotron.

The knowledge gained from this first-of-its-kind analysis may lead to even more efficient fuel cells that could, in turn, make utility-scale alternative energy systems more practical.

Role of electrons

In a typical fuel cell, the anode and cathode are separated by a gas-tight membrane. Oxygen molecules are introduced at the cathode where a catalyst fractures them into negatively charged oxygen ions. These ions then make their way to the anode where they react with hydrogen molecules to form the cell's primary "waste" product:  pure water. To perform both of these reactions, electrons also need to make the journey: electrons are added to the cathode and removed from the anode. Normally, the electrons are drawn to the cathode and the ions are drawn toward the anode, but while the ions pass directly through the membrane, the electrons can't penetrate it; they are forced to circumvent it via a circuit that can be harnessed to run anything from cars to power plants.

Because electrons do the designated "work" of fuel cells, they are popularly perceived as the critical functioning component. But ion flow is just as important, said Chueh, a center fellow at Stanford's Precourt Institute for Energy.

 "Electrons and ions constitute a two-way traffic pattern in many electrochemical processes," Chueh said.  "Fuel cells require the simultaneous transfer of both electrons and ions at the catalysts, and both the electron and ion 'arrows' are essential."

Electron transfer in electrochemical processes such as corrosion and electroplating is relatively well understood, Chueh said, but ion flow has remained, well, opaque. That's because the environment where ion transfer may best be studied – catalysts in the interior of fuel cells – is not conducive to inquiry.

Solid-oxide fuel cells operate at relatively high temperatures.  Certain materials are known to  make superior fuel cell catalysts.  Cerium oxide, or ceria, is particularly efficient. Cerium oxide fuel cells can hum along at 600 degrees Celsius, while fuel cells incorporating other catalysts must run at 800 C or more for optimal efficiency.  Those 200 degrees represent a huge difference, Chueh said.

"High temperatures are required for fast chemical reactivity," he said. "But, generally speaking, the higher the temperature, the quicker fuel cell components will degrade. So it's a major achievement if you can bring operating temperatures down."

Why does it work?

But while cerium oxide established itself as the gold standard for fuel cell catalysts, no one knew just why it works so well. And that paucity of data is troublesome: better understanding could lead to the fabrication of even better catalysts. What were needed were visualizations of ions flowing through catalytic materials. But you can't exactly stick an electron microscope into the pulsing, red-hot heart of a fuel cell running at full bore.

"People have trying to observe these reactions for years," Chueh said. "Figuring out an effective approach was very difficult."

In their Nature Communications paper, Chueh and his colleagues at Berkeley, Sandia and SLAC split water into hydrogen and oxygen (and vice versa) in a cerium oxide fuel cell.  While the fuel cell was running, they applied high-brilliance X-rays produced by Berkeley Lab's Advanced Light Source to illuminate the routes the oxygen ions took in the catalyst.  Access to the ALS tool and the cooperation of the staff enabled the researchers to create "snapshots" revealing just why ceria is such a superb catalytic material:  it is, paradoxically, defective.

"In this context, a 'defective' material is one that has a great many defects – or, more specifically, missing oxygen atoms – on an atomic scale," Chueh said.  "For a fuel cell catalyst, that's highly desirable."

Such oxygen "vacancies," he said, allow for higher reactivity and quicker ion transport, which in turn translate into an accelerated fuel cell reaction rate and higher power.  

"It turns out that a poor catalytic material is one where the atoms are very densely packed, like billiard balls racked for a game of eight ball," Chueh said. "That tight structure inhibits ion flow. But ions are able to exploit the abundant vacancies in ceria. We can now probe these vacancies; we can determine just how and to what degree they contribute to ion transfer. That has huge implications. When we can track what goes on in catalytic materials at the nanoscale, we can make them better – and, ultimately, make better fuel cells and even batteries."