Capturing the Sun

William Chueh has traveled thousands of miles throughout the United States to pursue his passion of nature photography, often hiking deep into remote canyons to snap the perfect picture. But when it came time to choose a graduate school, he decided to stay put at his undergraduate alma mater, Caltech, summoning his love of nature and concern for the environment as a guide.

In 2005, Chueh, then a Caltech senior, applied to graduate school in the Institute's Division of Engineering and Applied Science, and in his application, he recalled an event that would inform his research path. Two years earlier, he wrote, he had made a trip to the iconic Yosemite Valley. He was anticipating pristine views, but what he found instead was a curtain of smog thrown up by thousands of cars and buses passing through. His goal as a graduate student, Chueh wrote, was to help fix that problem. Today, he's made significant progress toward that goal.

This month, after five years in the lab of Professor of Materials Science and Chemical Engineering Sossina Haile, Chueh wrapped up his doctoral research—work that included developing a novel method of using solar energy to generate fuel. That breakthrough recently earned him a prestigious Truman Fellowship at the Sandia National Laboratories in Livermore, California. Chueh is the first Caltecher to receive the three-year, $800,000 fellowship, which will give him the freedom and funding to pursue a line of research that may lead to crucial advances in the production of abundant, clean energy.

Chueh started his freshman year at Caltech shortly after 9/11, amid considerable discussion about America's critical need to wean itself off fossil fuels. One of the recommended areas of research concerned ways to improve energy conversion and storage, and Chueh got hooked on the subject.

"If you throw fuel and oxygen in an engine, it burns in an inefficient and dirty way," Chueh says. "But if you use electrochemistry and do it in a more controlled manner, then you will have better efficiency and lower emissions." During his senior year, he assisted in a research project led by Haile, who had been studying ways of improving fuel cells, which convert fuel into electricity through a chemical reaction.

One of the problems with many fuel cells concerns temperature. Some can only operate at such high temperatures that they must be encased in expensive ceramic materials to withstand the heat, while those that can operate at close to room temperature need precious, scarce metals such as platinum to work. Another problem is that they need fuel—typically hydrogen derived from fossil fuels—to generate electricity.

Chueh holds three samples of metalized, thin-film cerium oxide, which he and Haile used to study the fundamental chemistry for generating fuel from the sun's heat.

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Chueh holds three samples of metalized, thin-film cerium oxide, which he and Haile used to study the fundamental chemistry for generating fuel from the sun's heat.

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Tackling the first problem, Haile had been investigating materials that would also allow fuel cells to work at lower temperatures. One of them, cerium oxide (CeO₂), is derived from the element cerium—which is classified as a rare earth metal, but is actually as common as copper. Cerium oxide plays an important role in a car's catalytic converter, helping to turn smog-causing molecules into carbon dioxide.

Shortly after Chueh joined Haile's lab as a graduate student, he and Haile started talking about whether CeO₂ could also play a role in using the heat of the sun to convert a chemical "cocktail," consisting primarily of carbon dioxide (CO₂) and steam, into a gas mixture of carbon monoxide and hydrogen known as "synthesis gas." This "syngas," as it's commonly called, can then be converted into liquid fuels through a decades-old process involving a series of chemical reactions.

"I was pessimistic at first," Chueh says. For a while he held off on testing the idea, but at Haile's urging, he decided to run the necessary experiments during winter break in 2007, when everyone else in the lab was on vacation. "It worked right off the bat," Chueh says. "I'm very cautious, though, so I repeated it before I told her about it. We were all very excited by the results."

Currently, says Chueh, "I'm working on experiments to demonstrate that this is not just a laboratory curiosity, but a solution that could potentially work on a larger scale." The process could also be used in a variety of applications, including the production of fuel for transportation and for running factories.

"William is a truly remarkable researcher, combining exceptional experimental talent with deep theoretical insight," says Haile. "This has allowed him to transform a loosely defined idea from a few sketches on a piece of paper to a meaningful scientific and technological breakthrough. I look forward to learning of his latest discoveries as he moves on to the next stage of his career."

At Sandia, a government-owned facility that develops technologies that support national security, Chueh will continue to study the cerium oxide–reaction to try to determine exactly what is happening at the molecular level while the catalyst is working. "Once we have a more detailed picture of that, we will be able to better understand why it works," he says, and possibly come up with ways to improve it.

Chueh says that he's "convinced that in the years to come, we'll see scaled-up plants that are actually producing a good amount of fuel from this kind of process. This system would work best in the desert, where there's lots of sun."

While Chueh acknowledges that there are numerous other solar research projects that could prove to be as beneficial as the cerium process, he says, "Every system has its advantages and drawbacks. In the end, a solution to the energy problem will not come from a single technology but from a wide range of technologies. This gives consumers and policy makers one additional option."

As for the nature photography that started it all, Chueh didn't have much time for his hobby during graduate school, but he's looking forward to taking it up again.

"I'm hoping to go to the eastern Sierra in the fall when all the aspens turn yellow and then orange," he says. "In nature photography, I love finding order in chaos, and that's what we essentially do in science.

"Deep down, I have a great appreciation for the environment," Chueh says. "When I saw that smog-filled Yosemite Valley, that's when I thought, 'I've got to do something before all this gets wiped out.'"