Development of solar fuel: Q&A with Dr. Jillian Dempsey

Assistant Professor Jillian Dempsey of UNC-Chapel Hill can make fuel with two ingredients: water and sunlight.

Dempsey’s research team is studying solar fuel in order to store the energy given off by the sun in an efficient manner. Below, she discusses what her team hopes to accomplish in the coming years through their research.

(This interview has been edited for length.)


Lydia Odom: What sparked your interest in solar fuels?

 Dr. Jillian Dempsey: When I was an undergraduate student I started doing research in a lab and that was one of the labs that was at the forefront of developing this technology. So I did research in this area when I was in college and I got really interested in it. When I went to graduate school I joined another lab where I could continue this research area. Then after that kept moving further and further into the field. It was just a really exciting area to be in as we think about the threats to our energy security and our global health. It’s a little scary to think about what happens if we don’t develop this technology, so that was a big motivating factor to go in this direction.


Odom: Can you explain, in layman’s terms, what you’re researching and what the goal behind your research is?

Dempsey: My research focuses on ways to capture solar energy and covert it into a stored form, specifically fuels. A lot of solar energy technologies that are currently available are things like solar photovoltaic, like solar panels. Those are great technologies, but obviously they could be a lot better because they’re expensive and their efficiency is not that great. But kind of a bigger challenge toward their widespread implementation is the storage. Solar panels generate electricity, but when the sun is not shining you’re not generating electricity, so how do you address that challenge?

My area of research is solar fuels, or artificial photosynthesis. What it is is using the energy of the sun to synthesize high energy density fuels. A great reason why it’s called artificial photosynthesis is because green plants are taking sunlight, water, and carbon dioxide and they’re using the energy from the sun to turn the carbon dioxide and the water into carbohydrates, or sugars, and oxygen. And when you generate these carbohydrates, that’s stored energy. So what we’re trying to do is something along those lines. We want to do a much simpler reaction, and instead of making sugars, which are complex molecules and require a PhD in organic chemistry to make, we want to do something simple like spitting water into hydrogen and oxygen … The splitting of water into hydrogen and oxygen is a endergonic reaction, so you have to put energy in to do that reaction and then the products are essentially storing the energy of the sun. And if you were to take that hydrogen and combust it, you would release all the energy … So we’re just trying to close that loop there. If the energy in to make hydrogen comes from the sun, then when we combust hydrogen we get energy back out.


Odom: In what form is the fuel you’re making? Is it a gas?

Dempsey: If you use it to make hydrogen, you are making a gas. Now that’s a challenge, because we like liquid fuels. So there are ways to couple this reaction with carbon dioxide… If you take carbon dioxide along for the ride there you could make products like methane or methanol. … But knowing that hydrogen is probably going to be an important fuel, there are a lot of people who have developed new materials for hydrogen storage…in order to make hydrogen a viable fuel.


Odom: Have you found anything in your research so far that may lead to this being a viable fuel?

 Dempsey: A lot of what my lab does is we study the very fundamental processes that are associated with building a device. So we’re not engineers, we have not built a device. But we think about how to make this process energy efficient. So imagine you are a catalyst and you take in sunlight. Now, sunlight has a certain energy, so every photon that hits the earth has a certain energy. We want to make sure we’re not wasting the energy that comes in in those photons. So what we’re trying to do is figure out ways that the catalysts won’t waste energy. We want to make sure that when they take the energy from that photon, they turn all the energy from that photon into fuel energy. We want to maximize that energy conversion process. We’re trying to work on the little details that make a big difference in the efficiency.


Odom: What are the main obstacles in scaling this up to be viable in the future?

Dempsey: A lot of the challenges with all solar technologies, this goes for the silicon solar panels we see now as well as the solar fuels, are the costs behind the materials that are needed to make these devices. One of the reasons we don’t see more solar panels is because of their high cost. And that comes from the materials needed and the processing for them. … A lot of what we have to do is figure out how to get cheaper materials, like nickel and iron, to behave like the expensive materials. Because not only are those materials expensive, part of the reason they’re expensive is because they are not very abundant on earth. They’re very rare materials. And they’re rare so their price goes up. But even if we had money, the fact that they’re rare means that we don’t even have enough of those materials on earth to fill the need.


Odom: What do you see as the main strength of this new technology, and why it might be able to overcome these obstacles?

Dempsey: There are a lot of advantages. It clearly addresses the storage issue. And also, because we’re making fuels, it addresses energy needs in the transportation sector. Another benefit of this technology is the fact that you don’t need to be on the electrical grid to utilize it. … In developing countries that don’t really have that electrical infrastructure but are rapidly becoming more and more developed and using more and more energy, this is a great opportunity for them. … And the last benefit I’ll note, is that you can start with saltwater or sewage waste water and make hydrogen. And then, when I release hydrogen though combustion or use hydrogen in a fuel cell, either way the product is clean water. So kind of the bonus is water purification.


Odom: Is there a time frame you see all of this happening in?

Dempsey: I would say maybe 15 to 20 years before this is something we’re seeing in the market. …People are being more optimistic than that and I am not as optimistic as other people, just because I’ve watched the process in 10 years very closely. So I know how far we can get in another 10 years, and that’s not enough.