Artificial Photosynthesis: An Interview with Daniel Nocera

AMIR BITRAN

Leaf
Photo by Yeong Suejan via Flickr. Creative Commons Attribution.

Daniel Nocera is the Patterson Rockwood Professor of Energy at Harvard’s Department of Chemistry and Chemical Biology. Nocera has achieved worldwide acclaim in renewable energy circles for his work on artificial photosynthesis, a biologically inspired method of harnessing solar energy to produce renewable fuels. Nocera’s take on photosynthesis incorporates an “artificial leaf”, which uses energy from sunlight to split water into hydrogen and oxygen, much like real leaves.  The hydrogen is subsequently fed into specialized hydrogen fuel cells1 to produce electricity. Excess hydrogen can be used in fuel cells even while the sun isn’t shining, solving a major weakness of traditional solar methods. In this interview with Brevia, Nocera expresses his hopes and concerns for this technology, as well as the global energy future.

AB: What made you look towards plants as a source of inspiration for renewable energy?
DN:  So photosynthesis is actually lousy at storing energy. But plants are really good at using energy efficiently. So what we did is, we looked at photosynthesis and asked, how can we take all the functional steps and put them together to make a good storage machine? And there were real lessons to be learned there. Plants are really good at taking sunlight and using that energy to create an electric current. The current splits water into oxygen and hydrogen. …[W]hat we decided to do is, stop there. Once you have hydrogen, you can make any fuel subsequently. [This is in contrast to plants, which use their excess hydrogen to make glucose.]

AB: How does your artificial leaf work? How is it different from your average rooftop solar panel?
DN: The artificial leaf is an energy storage technology; this is totally different from solar panels, which are energy generating. [Our]  technology has sunlight go to a fuel, which you can then use any time you want. Our technology is called a buried junction– you use the silicon of a solar panel to make a wireless current, and bury it between two conducting surfaces. Then you [place] catalysts, or compounds that can collect that charge and do the fuels transformation [i.e. split water into hydrogen and oxygen].

AB: Storing solar energy in the form of hydrogen seems like a great solution to perhaps the biggest hurdle of solar power: the sun doesn’t shine when it’s dark or cloudy. So why hasn’t hydrogen-based energy storage taken off yet? 
DN: The problem there is, there is no infrastructure for you to use the hydrogen. And there’s nothing you’re going to make that, at the snap at the finger, will replace trillions and trillions and trillions of dollars of investment that have already been paid out building our current energy system.  But in the developing world, they haven’t made that decision. Instead, they’re going to a decentralized energy system2, where you might have one hut generating the energy for a little village.

AB: So if developing nations successfully adopted decentralized energy, would developed nations follow suit and decentralize, potentially making room for hydrogen infrastructure?
DN:  Yeah, we’re going to get really jealous when we see a bunch of people we consider in the developing world living better than us.

AB: A key feature of your artificial leaf is that it splits water into hydrogen. But if clean water is scarce in developing nations, does dirty water damage your technology?
DN: That, we’ve solved. We really listen to plants–plants use kind of dirty water. And they can [do this] because they’re self-healing; they fix themselves [in case of damage].  So part of our invention was, could we make a self-healing technology? And we’ve developed a huge scientific ruleset for self-healing, and it’s now very predictable, and you can design self-healing.  Because we made a self-healing system, our technology can literally take a puddle off the ground.

AB: As a source of energy, where does artificial photosynthesis stand in terms of efficiency? Carbon neutrality?
DN: The latest thing we came up makes hydrogen and oxygen at 10% efficiency [10% of the solar energy that strikes the artificial leaf is successfully converted into fuel]. But we’re continuing to improve it.  We’re also exploring how we can combine hydrogen with other sources, such as CO2, to make different fuels. Say I’ve split water to hydrogen and oxygen. In a fuel cell, I can recombine these to produce electricity. But we don’t even deal with carbon. In the second scenario, I take the hydrogen and combine it with carbon dioxide from the atmosphere, and I make a fuel. But then you’re going to burn it, and the CO2 is going to go back in. So it’s carbon neutral [the net amount of CO2 in the atmosphere doesn’t change].

AB: What advice do you have for our readers who are interested in tackling the energy crisis?DN: So first, scientifically, you should join labs. And then, my other advice, which I feel pretty strongly about, is to get really good at something. So one danger of this area is, “oh, energy is really complicated, so there is science, and technology, and invention, but then there’s policy, government,” and that all might be true, but when you’re a student, you shouldn’t be trying to do all forty things at one time. The energy landscape is so broad, if you think of a funnel. But it is good to start at the bottom of the funnel, and then give yourself time in your own life, and let it open up. And the way that happens is being a good listener.

This interview has been edited for length and clarity.

 Works Cited:

  1. “Hydrogen Energy.” Hydrogen Power and Fuel Cells. Web. 22 Jan. 2015. <http://www.renewableenergyworld.com/rea/tech/hydrogen>.
  2. “How Microgrids Can Help Developing Nations Leapfrog the Landline.” GreenBiz. 1 Aug. 2013. Web. 22 Jan. 2015. <http://www.greenbiz.com/blog/2013/08/01/how-microgrids-can-help-developing-nations-leapfrog-landline>.

Amir Bitran is a Brevia Primary Research Co-editor. He can be reached at amirbitran@college.harvard.edu.