MIT announced on Thursday afternoon a new method of splitting water into hydrogen and oxygen, predicting that it will unleash a "solar revolution." And they're partly right. The research, which appears in the new issue Science, has little to do with solar power as we usually think of it. But it has wide-reaching implications as a storage medium, making renewable but
intermittent energy sources like the sun and wind more practical for everyday use.
The work, by MIT professor Daniel Nocera and his postdoc Matthew Kanan, follows several decades of work in a field sometimes known as "artificial photosynthesis," because it attempts to mimic one of nature's best tricks-storing energy in chemical bonds. In this case, energy from the sun can be stored in hydrogen when it is split from water; Nocera and Kanan have developed a catalyst for doing that more cheaply and efficiently.
The news is perfectly timed to catch a wave of enthusiasm for all things solar, as a number of different sun-powered technologies are finally approaching maturity as scalable and cost-effective options. Companies like First Solar have succeeded in bringing second-generation, silicon-free solar panels to the market at half the cost of traditional silicon panels, and the
first in a wave of utility-scale plants for solar-thermal energy went online outside Las Vegas last year. MIT itself is so excited about solar power that it has announced no less than three solar revolutions in the last six weeks, starting with "the most cost-efficient solar-power system in the world" on June 18, and adding "a new approach to harnessing the sun's energy" on July
10.
But in many ways, today's announcement isn't the latest in a string of solar breakthroughs-it's actually a piece of good news for boosters of the much-maligned "hydrogen economy." With Honda ramping up production of its FCX Clarity fuel-cell car and GM testing a fleet of its Chevy Equinox prototype, it's clear that hydrogen still has plenty of potential as a fuel-storage medium. Nocera's catalyst raises hopes-if not hype-that everyone with a roof could someday have a simple way of making hydrogen from water.
How It Works
Water is H2O-two hydrogen atoms and an oxygen atom-and scientists have known for two centuries how to apply a jolt of electricity to split it into hydrogen and oxygen, a process called electrolysis. What Nocera's scheme promises is a way of doing what existing commercial electrolyzers do, but much more simply and efficiently.
"Conceptually, it's the same thing," Nocera says. "But instead of feeding electrons into a hermetically sealed box filled with a concentrated base, we can feed them to an electrode sitting in a simple glass of water, at room temperature and pressure, with neutral pH." That simple setup makes it easy to build, operate and maintain.
Just as importantly, the catalyst identified by Nocera and Kanan uses cheap and abundant materials-cobalt and phosphorous-instead of the rare and expensive metals used as catalysts in existing systems. That's crucial, since the question isn't whether we can split water (we already know we can), but whether we can do it cheaply enough to install a system in every
house.
The new catalyst actually facilitates the production of the oxygen byproduct. That's half the battle-a separate catalyst for hydrogen production is the other half-but it's crucial to making the whole process work. "You can't complete the circuit unless both parts are working," explains Tom Mallouk, a Penn State chemistry professor pursuing similar goals.
The search for a cheap, efficient oxygen catalyst has lagged far behind the development of hydrogen catalysts, according to University of California-Irvine professor Alan Heyduk, who worked with Nocera as a graduate student but wasn't involved in the current research. "This has been a bit of a holy grail," he says.
Mallouk agrees: "My group has been working on this as well, but so far we have been using relatively expensive elements to make it work. That's fine for proof-of-concept, but not much use in the real world."
The Storage Breakthrough
Hydrogen is often thought of as a fuel for hydrogen cars, but its role is actually much broader: It's a way of storing energy. That's particularly attractive for solar power, the great weakness of which Kanan and Nocera, in their Science paper, call "the diurnal variation in local insolation"-in
other words, the fact that the sun goes down each night.
It's worth noting that Nocera's current experiments didn't use solar energy-they simply ran off electricity from the grid. That's actually an advantage, since it means the same technology could be used to make hydrogen with wind turbines or other renewable sources like hydropower.
In Nocera's solar-based scheme, photovoltaic (PV) panels on a home would provide its residents with electricity during the day, while at the same time splitting water into hydrogen and oxygen. When the sun goes down, a fuel cell would combine the stockpiled molecules to continue to provide power. MIT's press release predicts that, within 10 years, "electricity-by-wire from a central source will be a thing of the past."
The problem of how to store solar energy-or any energy at a large scale-is very real. Batteries are simply too expensive and don't yet have enough capacity. The Andasol solar thermal plant in Spain will test one interesting option later this year: Liquid heated by its mirrors will be stored in what is essentially a giant Thermos, so that the plant can continue to generate six hours of electricity each night. Abengoa recently announced a similar plant in Arizona; thermal storage will power the air-conditioning usage peak that continues after sunset in the Southwest.
Nocera's scheme has several advantages, though. Because it can work on a small scale, it's suitable for distributed power in homes. Hydrogen is also versatile enough to be used in other applications, such as fuel-cell cars.
Next Steps
There's no question that finding a clean, cheap and efficient way of making hydrogen would be transformative-which is why the Department of Energy's Hydrogen Program is funding literally dozens of possible ways of doing it. The question is which one will be cheapest and most efficient.
Nocera says that, with the publication of these results, he's confident that scientists and engineers will rush to advance the design, pushing it toward practicality within the next 10 years. He may be on target, except that virtually every one of the hydrogen-production projects funded by the DOE has entertained similar hopes; otherwise they never would have obtained
funding.
The next move for Nocera's team will be to build a more efficient version of their current device-one that reduces the physical distance between the two electrodes. Then they plan to design a version that is actually powered by PV panels. "The basic science is done," Nocera says, referring to the new catalyst. "Now it's engineering."
That, unfortunately, is the stage at which innumerable great ideas for alternative energy sources have met their demise. That includes earlier attempts to mimic photosynthesis by using the sun's energy to produce hydrogen-research that experienced a vogue in the 1970s when early
proof-of-principle experiments showed promise. In that case, the engineering didn't work out.
Of course, that doesn't mean it won't work out this time, or that the new results aren't cause for enthusiasm. "The only people this isn't good news for is people who dig oil out of the ground," UC Irvine's Heyduk says. Mallouk's endorsement was even more direct: "I already e-mailed [Nocera] this afternoon to see whether the new catalyst would work in my system."
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