The Proton Phenomenon
Prof. Miriam Bowring investigates ways to liberate hydrogen from its bonds.
Hydrogen is the perfect fuel—if you can get it right. Pound for pound, it boasts more energy than any other combustible material— more than three times the energy content of gasoline. It burns cleanly, combining with oxygen in the atmosphere to produce water as its only exhaust. And there’s plenty of it around (it is, in fact, the most abundant element in the universe).
But getting it right is not easy. Hydrogen is costly to produce and notoriously difficult to store (partly because it’s so light, and partly because of its explosive personality). Just ask Prof. Miriam Bowring [chemistry 2016–], who recently won a three-year, $43,500 research grant from the Murdock Charitable Trust to study catalysts that could revolutionize the production and storage of hydrogen.
The catalysts Prof. Bowring studies bypass the energy constraints that make conventional hydrogen production so expensive by exploiting a quirk of quantum mechanics known as proton tunneling. Or, at least, “People think that it does,” she is quick to say, hedging like any good scientist. “What we’re doing, in the long term at ÌÇÐÄvlogÊÓƵ, is trying to find out—is proton tunneling something that’s really happening? How do we know it’s happening? Can we do something useful with it?”
It’s too early to know the answer. But the potential implications are huge.
At first glance, proton tunneling—the spontaneous teleportation of a proton from one location to the other—is little short of miraculous. But it is in fact a direct consequence of basic quantum mechanical principles. “At the atomic level, particles do not exist in the same way that we imagine objects that we interact with in normal life,” says Zac Mathe ’17, one of Bowring’s former thesis students, who is now pursuing a master’s in chemistry at the Max Planck Institute for Chemistry in Germany. “In particular, they do not have defined boundaries or an exact spatial location. Instead, we have to think of, for example, an electron, existing as a probability distribution. It doesn’t exist in one place. It’s in a range of places.”
As a result of this blurriness, subatomic particles that are most likely to be on one side of a barrier occasionally show up on (i.e.,tunnel through to) the other, like minuscule ghosts. But the barriers in this case are not made of bricks but of energy—the energy requirements that prevent chemical reactions from happening. “By a classical mechanism, you may have to put a lot of energy into a reaction to get it to happen,” Zac says. “With tunneling, you don’t have to do that. You can get from A to B without ever having to put in enough energy to exist in the middle.” The smaller the particle, the more likely it is to undergo tunneling; photons, which are massless, tunnel more often than electrons, which have the mass of about two nonillionths (30 zeroes after the decimal point) of a pound. Protons are nearly 2,000 times more massive than electrons, but also appear capable of quantum tunneling. Preliminary studies suggest that enzymes in the human body—and likely throughout all forms of life—actually depend on proton tunneling to break down and combine essential molecules.
In the world of chemistry, protons are better known in their role as the sole member of a hydrogen nucleus, and proton tunneling implies that, under the right conditions, hydrogen may spontaneously react by jumping from its bond with one atom to another even when the energy necessary for that jump isn’t present.
In 2010, researchers in Professor Shunichi Fukuzumi’s lab at Osaka University were studying the ability of a catalyst containing the metals iridium and ruthenium to generate hydrogen gas from water. They did an experiment with “heavy” water—water made up of oxygen and deuterium, a rare isotope of hydrogen that boasts a neutron in its nucleus—to produce deuterium gas instead. Chemically, deuterium is identical to regular hydrogen because it has the same number of protons. “We’d expect hydrogen and deuterium to basically do the same thing,” says Bowring, “but sometimes they don’t.”
Comparing heavy water to regular water, Fukuzumi’s team discovered that the catalyst generated deuterium gas 40 times more slowly than it generated hydrogen gas. Their explanation? The heavier deuterium was less likely to exhibit quantum tunneling because it has twice as much mass. In other words, quantum tunneling was the reason why the iridium-ruthenium catalyst worked so well. Bowring was intrigued, though skeptical. So she set out to investigate.
Bowring brings a wealth of research expertise to her quest. She earned her BS in chemistry from Yale and her PhD from UC Berkeley. She worked as a postdoc at Yale and the University of Washington, where she focused on quantum tunneling. But she also has a knack for teaching.
“She taught me everything I know,” says Jo Keller ’20, who spent the past summer working in Bowring’s lab. “Miriam is a great teacher, a great mentor, in and out of the lab.”
Bowring’s teaching philosophy resembles the phenomenon she studies: she presents her students with obstacles and trusts them to figure out how to get to the other side. “At the beginning of my summer, I came to Miriam with a few different ideas of how to separate two products of a reaction from each other,” Jo says. “She asked me, ‘Have you considered optimizing the reaction instead?’ A few days later, I came back to her with a plan that included optimization. I was more excited about trying other techniques before optimization, which was intimidating.”
When Jo’s attempt to separate the products of a reaction by straining them through a column of silica gel did not go as planned, Bowring explained her thinking. “‘I probably would have started with optimization,’” Jo remembers her saying. “‘But the separation was useful. You learned a lot.’”
Oleks Lushchyk ’17 wrote their thesis on palladium catalysts last year with Bowring. Now they work as a substitute teacher in Alaska and hope to get a teaching certification and teach full time. “My time with Miriam really prepared me for doing this kind of teaching,” Oleks says. “She did some good guiding as to what she thought would work and wouldn’t work. You don’t want to hold students’ hands the whole way, but you do want to guide them in the right direction.”
Oleks attributes Bowring’s teaching style to her experience outside the lab. Between Yale and Berkeley, she taught high-school chemistry for two years at an independent school in Massachusetts. Oleks borrows from her pedagogical approach every day. “When I work with students, I don’t tell them, ‘You’re doing that wrong, you’re doing this wrong.’ I ask them, ‘Do you need help?’”
Bowring is as dedicated to the craft of teaching as she is to the science of chemistry. At Berkeley, she won awards from the nonprofit Community Resources for Science for her work as a volunteer teacher in Bay Area classrooms. As a PhD student, she went beyond standard grad-student duties and took on undergrad and high school mentees each year. She served as a volunteer outreach teacher for the National Science Foundation during her postdoctoral research at the University of Washington, and—in the most literal manifestation of her hands-on approach—volunteered as a women’s ultimate frisbee coach at Yale.
For the thesis student of a new chemistry professor, building a lab from scratch is part of that hands-on experience. “A great part of working with Miriam for me was feeling like I was part of the process of building a lab,” Zac says. “For the first half of my thesis, more often than having a flask in my hand I had a wrench in my hand.”
Though these obstacles were sometimes frustrating—for instance, working for three days to find a leak in an instrument that creates a vacuum when functional versions of the same instrument exist in labs down the hall—Zac is grateful for having had the chance to learn from Bowring. “ÌÇÐÄvlogÊÓƵ science gives you a very strong theoretical background—it is ÌÇÐÄvlogÊÓƵ,” they say. “I was lucky that I also got a lot of very practical experience, experience solving physical problems with things in front of me, that made me a much better scientist. I only got that experience because I was in Miriam’s lab.”
Bowring and her students are working hard to investigate the riddle of proton tunneling. “What I’m trying to do is find examples where someone found a huge isotope effect and replicate it in our lab,” she says. “Can we simplify the system that they’ve seen it in and study it and tweak it? Can we do anything to make the isotope effect go away, or get bigger, or smaller?” To start, she eliminated much of the complexity of Fukuzumi’s catalyst by more or less chopping it in half and studying how the iridium half of the compound functions on its own.
The resulting iridium compound is an organometallic “half-sandwich complex.” The “bread” is a ring of five or six atoms of carbon that can have various extensions attached (these structures are known as “aromatic rings” even though they do not always have an odor). The “meat” is the iridium atom. A full-sandwich complex consists of two such rings with a metal atom in between.
These iridium half sandwiches can combine carbon dioxide and hydrogen to store the fuel as a safe intermediate—formic acid—and then break apart that intermediate to regenerate hydrogen. Even better, they are capable of running the reaction both ways at room temperature. “A reversible catalytic system that could store hydrogen as formic acid and release it when you need it, and store it back again using CO2, that could be really useful,” Bowring says.
That’s an understatement. The Japanese chemists who filed a patent application for the catalysts described them as “epoch-making.”
Iridium sandwiches significantly reduce the amount of energy required to generate hydrogen and make it possible to store the fuel in the form of the relatively benign formic acid. As an added bonus, one of the feedstocks for the process is carbon dioxide. Unlocking the secrets of proton tunneling may be the key to making hydrogen a viable fuel—and finding a new use for a greenhouse gas that plays a key role in climate change.
Kieran Hanrahan ’15 lives and works in Portland with his dog, Lily, and his growing collection of spiders.
Tags: Professors, Research