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Artificial Leaf

Originally posted at climatecentral.org
By Alyson Kenward

A couple of weeks ago, the social media networks were buzzing over the announcement of new technology that uses sunlight to split water for energy purposes; the so-called “artificial leaf.” It’s a man-made form of photosynthesis, a water-splitting technology that could potentially overcome the big challenges facing solar energy, like its current costliness and inability to provide energy when the sun goes down. MIT chemist Daniel Nocera unveiled the new artificial leaf at a recent American Chemical Society annual meeting, but many of the people commenting on it in the press didn’t have the opportunity to see the technology in action.

As a trained chemist, I wanted to reserve judgment until I could see this invention for myself. Lucky for me, this weekend I had the chance. And I have to say it was pretty impressive.

On Saturday, Nocera gave a lecture in Princeton, N.J. (where Climate Central has one of its offices) as part of a symposium honoring the university’s new chemistry building. The symposium was focused on the big problems the chemistry community should be tackling in the years ahead, and it’s not surprising that three talks, including Nocera’s, were directed at making solar energy more affordable and widely available.

Nocera’s presentation in particular was a show-stopper. He demonstrated via video he can already make a bit of sunlight turn a glass of water (containing a small card made of silicon and a few other materials) into hydrogen and oxygen gas. It might not sound like anything too fancy, and it doesn’t look like any leaf I’ve ever seen, but it’s being described as the first time that a chemist has found what appears to be an inexpensive way to mimic what plants have naturally been doing for millions of years.

Through photosynthesis, plants convert sunlight into energy (albeit inefficiently) by splitting water up into its constituent parts: oxygen and hydrogen, and then storing these alternative forms of energy until they are needed later on. For humans, the goal is to do the same thing because hydrogen and oxygen can be recombined in a fuel cell to produce electricity whenever you might need it. It may also be possible to take the hydrogen and combine it with carbon dioxide (CO2) to make fuels resembling gasoline, similar to the way plants use the hydrogen to make sugars.

I should point out here that water-splitting itself is nothing new. It’s actually been around for decades, but most versions haven’t used sunlight (instead they have required electricity from the wall to achieve water splitting). Researchers from the Department of Energy’s National Renewable Energy Lab found a way to do solar-powered water splitting more than 10 years ago, but the materials in that example were, as Nocera calls them, “space-aged.”

In other words, crazy expensive and not appropriate for widespread use.

Nocera’s set-up, on the other hand, uses much cheaper materials. He hasn’t revealed the exact identity of his new catalysts (which are now being patented), but preliminary versions of his “leaf”, which have been published over the past few years, call on some of the cheapest metals around.

He has said for years that massive expansion of solar power is one of the only ways that the world will be able to meet its growing energy demands in a sustainable way. There are several energy analysts that don’t agree with him, instead saying that other sources of energy, like wind, geothermal and nuclear, must also play a big role.

Nocera’s argument, however, is that most of the new energy demand will be coming from the developing world, where building up solar power for individuals will be a more realistic option than other forms of energy.

“In the U.S., we’re stuck with this ball and chain of legacy energy,” he explained on Saturday. Nocera says that countries like the United States are so heavily invested in existing energy infrastructure that there isn’t much chance the country can easily switch to renewable options like solar. On the other hand, many developing countries completely lack a central electrical grid. People living in many parts of African and India, for example, still rely heavily on the direct combusion of coal, wood, or dung for fuel and don’t have access to electricity.

He says that if solar power technology can be mass-produced on the cheap, there won’t be any reason for developing countries to build massive power plants and thousands of miles of power lines. Instead, each household can have their own energy source. All they will need is a copy of the artificial leaf (albeit one larger than Nocera’s test version) and about 16 ounces of water.

How much water would be needed altogether to power the planet, if an inexpensive version of the technology is manufactured so everyone on Earth can have it? About the same amount as what’s in MIT’s Olympic-sized swimming pool, says Nocera. And this volume could be a one-time demand because, in theory, the water would be remade again in the fuel cell.

Of course, this is all still in ivory tower-territory, and it will be years before a commercial model of Nocera’s setup might be available (and there isn’t any guarantee it ever will be). But the fact that so much energy is stored up in the chemical bonds of water explains why so many chemists think that solar-powered water splitting is such an essential research goal.

At Saturday’s presentation, Nocera didn’t even begin to address exactly how long it will be before his technology, or a similar version of it, could be put to use in the real world. But one day earlier, during an interview with NPR’s Ira Flatow, he said it could be ready in less than a decade:

We’re building prototypes, and there’s a lot to still do because you need to make sure this can go for years, not days. It’s got to go for years. We haven’t had the time to test [it] for years yet.

It’s been going for days now with no drop in activity. So those are all the practical concerns of long-term because if you’re a commercial buyer, you’re a customer, you only use things that are reliable, and that can be the death knell of any technology. But we’re well beyond the science, and now we’re into the engineering and into the reliability game.

To get a sense of what Nocera’s talk was like on Saturday, have a look at this PopTech video from 2009. The video was filmed before he made the entire “artificial leaf” but it describes the motivation for water-splitting and also outlines the calculations on how much water is needed to meet the global energy demand (check out the 15-mark in particular).

Dan Nocera: Personalized Energy from PopTech on Vimeo.

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