Video: Uncut interview with Sossina Haile, Caltech
One of the biggest obstacles to creating a viable solar energy fuel cell involves finding the right catalyst. But what is a catalyst? And what makes the right one right? We spoke with the scientists working on the solar energy fuel cell. Here’s what they told us.
SOSSINA HAILE: A catalyst is something that makes something else happen faster. It [the something else] would like to do it, but it’s sitting there in what we call low-energy state. So, let’s say you’re sitting there in bed and you need to go to school and your mom comes in and tells you get out of bed because you need to go to school. That’s the catalyst in that scenario. This is something that was going to happen anyway, but just needed to be speeded up. So that’s what a catalyst does.
JONAS PETERS: The part that my research group is particularly interested in is making the catalysts that are needed to do two things: one, the catalysts are needed to help strip electrons and protons out of water, and then, as those electrons and protons would flow through a membrane in one direction, we’re going to need catalysts that allow the electrons and protons to recombine. And when they do that, they make hydrogen, and the hydrogen is the fuel that we need.
NATE LEWIS: People have known for a hundred years or more how to take electricity and water and make hydrogen and oxygen. Many people do this in high school chemistry classes. You take a battery, turn on the voltage, and out bubble hydrogen and oxygen. So we know how to take electricity, even from the sun in solar cells, and make chemical fuel. It just costs way too much to use the metals that we need to do that right now, like platinum and rhodium. Very expensive. And we won’t have enough of that to cover all the area needed to capture all the sunlight.
SOSSINA HAILE: We don’t, in principle, require platinum to make the fuel cell work. Now platinum is a precious metal. People know it because they use it for jewelry, but it’s used as a very critical component in most hydrogen fuel cells.
It’s used as a catalyst. If you look at what the Department of Energy targets are for the amount of platinum that would be needed, if you converted all of U.S. automobiles to platinum-based hydrogen fuel cells, you would double U.S. platinum consumption [and] double worldwide platinum consumption within a year. I mean, it would just be incredible.
You can make projections as to how many years it would take to run out of world platinum supply. And the irony of all of this is that hydrogen is discussed as a way to have energy independence. Turns out that U.S. platinum is 93 percent imported. Eighty percent comes from one mine complex in South Africa. Another 15 percent comes from one mine complex in Russia.
We’ve got to find another catalyst. And the way to do that, the simplest way to do that is to operate the fuel cells at slightly higher temperatures at which everything just works much faster. So kinetics go much faster. So you can get around the need for platinum.
JONAS PETERS: So there are catalysts that can split water and there are catalysts that can make hydrogen. … But we don’t have catalysts that sit right at the thermodynamic potential to drive the reactions without wasting a lot of energy. If you waste a lot of energy in driving these reactions, you’re not storing a lot of energy. And that’s what we want to be able to do. …We don’t currently have catalysts that need what we’ll call the minimal amount of energy to split water and make hydrogen. We have catalysts that require way too much energy. And therefore, they’re not solutions.
So we have to discover new catalysts that sit right at the sweet spot, and nature has actually evolved catalysts over millions and billions of years that do sit right at the sweet spot. And so, the fact is that the proof of principle has already been established, so the question is, can we learn from nature’s catalysts and figure out how to make synthetic catalysts that would be useful for the amount of fuel that humanity needs?
There are all these problems with figuring out what should those catalysts be, so that they work the perfect potential and they also last a very long time. And they have to be made of materials — earth-abundant materials that … shouldn’t be toxic and … have to be widely available.
Nature can do that reaction using iron and there’s a lot more iron on the planet, and so you might want to figure out how to make catalysts of iron because that would be, long term, a much better catalyst source.