The Power of Motion; Harvesting Energy from Freestanding Graphene

Bob Whitby: Hello and welcome to Short Talks From The Hill, a science and research podcast from the University of Arkansas. I’m Bob Whitby, a science writer at the university. This month, we’re checking back in with professor of physics Paul Thibado to get an update on his research into harvesting energy from freestanding graphene. Welcome, Paul.

Paul Thibado: Hello, thanks for having me.

BW: Great to have you back. So the last time we spoke with you was a couple of years ago when you were developing a theory on how energy could be captured from graphene. Before we find out what’s new, can you give us a refresher on exactly what is graphene?

PT: Yeah, good, so graphene is a single layer of carbon atoms, and the atoms are arranged in a honeycomb lattice structure, and so it looks a lot like chicken wire, actually. And you can get graphene from graphite. So if you if you take graphite, which is basically coal, and you kind of peel it, it’s very flaky, you thin it down. Eventually you’ll get down to one atomic plane of graphite and that is graphene.

BW: OK, and why is that of interest to science?

PT: Well, that’s a big question that goes way back. Long ago, it was predicted that if you make something too thin it would become unstable and would tear apart or melt. Actually, being three-dimensional is keeping it together. So it was kind of fun from a fundamental perspective, it was very interesting in 2004 when graphene was first isolated. But for our research, what’s very interesting is we take this single layer of graphene and we put it over a picture frame so that it’s freestanding in the middle of the frame, and it has very unique properties because it’s this sheet of atoms that never existed before. I mean, we have three-dimensional solids and we also have gas, a gas of atoms or fluid of atoms, but never before have we had a sheet of atoms. And what we found is that’s very interesting. Just like the atoms in the in the room are all moving around all the time because they’re at room temperature, well, this sheet kind of like a sheet of on a clothesline is waving around all the time as well because it’s so thin and so flexible, and that’s what’s been very interesting for us to study.

BW: So this motion is what you thought could be harvested for energy. And now you’ve successfully developed a circuit, is that correct?

PT: Yeah, so we spent, it’s been three years in the in the making here. We had the idea three years ago and it took us three years to get to this point. But basically, yeah, so we had to develop this energy-harvesting circuit and the way we did that was taking advantage of a property called a varying capacitance. So basically, we bring a sharp metal probe close to the graphene surface, and as the graphene is waving around all on its own just because it’s at room temperature, it causes the distance between this metal probe in the graphene to also vary, and when we apply a bias voltage between the two, what that does is it causes the charge on the graphene to increase when it comes closer to the metal probe and decrease when it goes away from the metal probe. So, we naturally form this alternating current and we can use that alternating current to power a circuit.

BW: OK, and you had the idea before, but now you’ve actually built the circuit. Can you tell us, I know it’s hard to explain something like that in a podcast, but can you give us an idea how it actually works?

PT: What we did to make it, really prove that it could be something useful, I think, is we connected the metal probe to diodes, these are gates essentially that allow current to flow only in one direction. So when the graphene is moving toward the metal probe and the current starts to flow, the charge on the graphene starts to increase by current flowing in the circuit and it’ll go in one direction and we isolate the flow of current using a diode. When it goes, let’s say clockwise. And then when the graphene flips away, the current will flow counterclockwise. But because of the diodes it is forced to go through a different path through the circuit, so we can tell when the graphene is moving toward or moving away because of the way the current flows through these diodes. And I should point out the big thing here that we’ve discovered was, it was predicted in the ’50s that if you had this type of what we call Brownian motion, this kind of thermal motion of the graphene, that for one it couldn’t be used to power a circuit. That was one thing, but if we connected it to diodes, the diodes would squash or reduce the amount of current flowing in the circuit just by their inherent property of acting like a gate. And it turned out that that theory that was done in the ’50s was completely wrong and that really they didn’t have the theoretical tools in the ’50s to analyze those nonlinear properties of the gate. And so those theories have just been recently developed really in the late 1990s, and so when we when we revisited that problem with the proper theoretical development, we found that the signal didn’t get squashed, but in fact got enhanced, enhanced by a factor of 10, or 100, or 1,000, depending upon how much, how big the fluctuations were. So that was a really big surprise, and a pleasant surprise, for us to that not only could we power the circuit, but in fact the nonlinear nature of the diodes enhances that power significantly.

BW: So you sort of rewrote the book a little bit on physics.

PT: Yeah, that’s exactly right. That was a big thing, that was a big paper that was out there in the ’50s, and Feynman, who has a famous lecture series that he did in the ’60s, basically talks about that in his famous Brownian Ratchet. And so yeah, so that’s a that was a bit shocking and surprising for us and got the paper that we published a lot of attention.

BW: What will this lead to? I think you mentioned earlier it could result in a battery replacement. Tell us about that.

PT: Yeah, so since the theoretical development was taking a long time, but we had the experimental data which showed it worked, so we felt confident from an experimental perspective. So we started moving forward in what we call miniaturizing this energy harvesting technology. The very first experiments were done in a in an ultra-high vacuum chamber that measures about 10-feet by 10-feet by 10-feet. What we wanted to do was reproduce the essential components of that experiment on a silicon wafer that was processed using standard processing technology that goes into making computer chips, and so we’ve been working on that. Actually for the last, well, almost the whole three years, really. And we’ve made a lot of progress there and in fact, in developing that technology, I would say we came up with two designs that we’re moving forward. One is kind of like a first-generation design that should produce power and be like a battery replacement, but it will be for really low-power applications. And then the second-generation design which we will be kind of working on in parallel. But it’s going to take longer. We’re hoping it will boost that power output to a higher level.

BW: And you would have something that could actually power a device?

PT: Yeah, so we were testing the circuit right now with really low power. You know, like a watch, like a standard watch that has a second hand moving around on it. You know this typically uses like a microwatt of power and so what we would like to demonstrate is that this these chips can power this watch, but the power source is the thermal environment not a battery. You know it’s actually just harvesting energy from the motion of the carbon atom as a result of being at room temperature.

BW: So it would never need replacing and it would produce power indefinitely.

PT: Yeah, I mean it was basically made from the same resistors and capacitors and computer chips are made of and those will last 20 to 50 years in harsh environments. It won’t produce a lot of power, but we think that we can have it. You know, it’s kind of like solar power, I guess, you know, in the sense that you can harvest this energy maybe you could store it and use it later. We kind of think of it a lot like solar power and wind power. You can harvest energy from solar power and wind power indefinitely, so this is kind of the same idea. People ask me all the time, “Is this like a perpetual motion machine, you know, it will run forever.” No it’s not, you know, solar power and wind power are not perpetual-motion machines in the sense that if the sun goes away then your solar power goes away and your wind power goes away, and the same thing with this thermal power. So it’s not a perpetual-motion machine, it is just taking advantage of all this extra heat that’s sitting around because of the sun heating the earth.

BW: Still seems like a really significant discovery. What’s been the reaction since you published the paper?

PT: Yeah, well, there’s been a huge reaction. Actually. I would say most of it’s been really positive. I mean, we’ve had a lot of news stories pick up the press release that the university did, and a lot of scientists have read the article that we wrote and I’ve been contacted by, you know, a whole bunch of people from enthusiasts to experts. I think that it’s going to give us a kind of a clear understanding of some physics that people knew about years ago, kind of like Johnson Noise or Nyquist Noise, but going to put that on a more solid foundation. With our latest understanding of this theory that was really put together in initial phases in the 1990s called stochastic thermodynamics, which allows us to understand these statistical fluctuations and how they relate to thermodynamic properties.

BW: It’s fascinating research and maybe by the next time we check in with you in a couple of years, you’ll have another exciting development to report.

PT: I hope so.

Matt McGowan: Music for Short Talks From the Hill was written and performed by local musician Ben Harris. For more information and additional podcasts, visit Arkansas Research. That’s arkansasresearch.uark.edu, the home of science and research news at the University of Arkansas.