Scientists have figured out how to harness Brownian motion – literally the thermal energy of individual molecules – to make electricity, by cleverly connecting diodes up to pieces of graphene, which are atom-thick sheets of Carbon. The team has successfully demonstrated their theory (which was previously thought to be impossible by prominent physicists like Richard Feynman), and are now trying to make a kind of micro-harvester that can basically produce inexhaustible power for things like smart sensors.
The most impressive thing about the system is that it doesn’t require a thermal gradient to do work, like other kinds of heat-harvesting systems (Stirling engines, Peltier junctions, etc.). As long as it’s a bit above absolute zero, there’s enough thermal energy “in the system” to make the graphene vibrate continuously, which induces a current that the diodes can then pump out.
Original journal link: https://journals.aps.org/pre/abstract/10.1103/PhysRevE.108.024130
It’s more like a generator that uses ambient heat as the “battery”. With previous systems you could only extract useful work from heat if you had a heat gradient (e.g. one area that’s hotter than another). With this invention the innovation is that graphene’s unique combination of thinness and conductivity basically let you convert the brownian “heat” of the substance itself (not the environment) into electricity.
This is genuinely incredible though. Because it means you can cool things even when there’s nowhere to dump the heat into, for example, space.
EDIT: Though in space you lose heat as infra-red, but only in limited amounts. Scaled up this technology would allow far better control letting you run more powerful equipment while also improving efficiency.
And you’re limited to approaching 2.7K, the background temperature and limit for radiative cooling, which is higher than you would want for some sensors. Being able to either extract power and charge a battery to be either used as power, to heat other parts of the craft, or to concentrate for more efficient radiation would be quite useful.
I couldnt access the full text, but that was my impression, too, based on the summary. It appears to work on some analog of hysteresis where the technical balance of energy is maintained but the time scale of restitution is long enough that power can be “siphoned off”. Again - since conservation of energy must be preserved and no matter is created or destroyed, this would serve to reduce the temperature of the graphene. There doesn’t appear to be a scale for their experimental work and whether they’re extracting pico amps or microamps across the (I guessing form the publicly available graphs) 0-0.4 volt potential.
It’s not clear if they’re looking at nominally uniform temperature material which has fluctuations in temperature due to the surroundings, or if they are inducing temperature gradients in the material intentionally to produce the signal. I’m an engineer, not a theoretical physicist, so anyone claiming to end-run the second law of thermodynamics is going to be treated with a bit of skepticism as to the practicality or scalability of this “cheat”.
I think this is it exactly, and in fact I found a Science Daily article that explains the cleverness of it (your assumption about the time scale is correct, and they have a clever arrangement of diodes that let you kind of “pump” the charge out). They specifically mention not violating the 2nd Law too :)
A law is only effective if the majority is following it. But we will never escape this system if we follow the rules of the system itself. I’m calling for scientists to finally just break the laws of thermodynamics!
I recall watching a video about this a few months ago. Their explanation of how this doesn’t violate the law of increasing entropy was not satisfactory:
They ran a computer simulation of their model that showed 0 entropy at the beginning then a huge spike and then an asymptotic approach to a steady state value. Since the steady state value wasn’t zero they said “look entropy increased (from zero to some value) we don’t violate the law of entropy”.
The initial entropy value of zero was because of fixed starting conditions ie at fixed starting conditions entropy is zero because you’ve defined the state everything is in. Once I figured out this have waving I lost interest.
Wouldn’t this just slowly cool the ambient temp around the material. I’m guessing there would be practical limits on how quickly this could create power but it doesn’t seem to be claiming to create free energy just extract it from ambient Temps no?
That’s actually a big deal, thermodynamically. They are claiming that they can reduce entropy essentially without an input or pump - their diode aray appears to be a Maxwell’s demon.
I mean isn’t the graphenes physical vibrations the input/pump in this situation powered by the ambient thermal energy radiating into the graphene? I’m only a software engineer so I apologize if some of this is just going over my head lol.
Hey, I’m just an aero/structural engineer - this microscopic and quantum level stuff is well outside of my daily practice, too. The theory (of which I am innocent of all detail) says that this shouldn’t be possible - using Brownian motion as a source (directly or as a pump). If this is an end-run around classic physics, that’s okay, as long as the overall energy balance can be shown to be maintained.
Edit: Usually in threads like this I hope to say something wrong, or apply the wrong principle, and then someone who is an expert comes in and corrects me. Then I go look up whatever it is they say and I get to learn something new for the day. Either that or someone who knows more than I do agrees with me and expands on the description in a really insightful way, and I get to learn something more in depth that day.
Oh that’s what this was reminding me of! Thank you.
I guess in addition isn’t the thermal gradient they are claiming is nonexistent just extremely small throughout the graphene molecules? They aren’t gonna be a perfectly uniform temperature and thermals don’t transfer instantly meaning a gradient would be present. I guess couldn’t you prove they aren’t reducing entropy by comparing how quickly the sheet of graphene cools when this system is active vs a regular sheet of graphene in the same conditions. I’d guess we would see their system losing heat more quickly than the plain old sheet of graphene thus showing this isn’t a maxwell demon?
This is exactly what it must be doing.
Graphene is above 0K -> the atoms have some thermal energy -> harvest some of that energy as electrical potential -> graphene cools down.
The most interesting application to me is that this could be use to remove heat at an interface without needing a thermal gradient to transport the heat.
I mean that depends on how quickly it actually cools down the ambient Temps no? Plus we still can’t make massive sheets of graphene if I am not mistaken so wouldn’t the scale of this make that impossible at this stage? I’d see the benefit for powering micro sensors via ambient Temps though.
I feel like I must be missing something here.
If you’re extracting energy from ambient heat without a temperature differential, then is that not a perpetual motion machine? Once you use that energy, 100% of it goes right back into the system as waste heat, ready to be harvested again. You can run this indefinitely and it will never reach absolute zero, so…what am I missing?
Sounds like from the properties of graphene they are able to turn its thermal energy to electrical so long as the material isn’t at absolute zero (obviously or then it would be a perpetual motion like machine), plus i dont see anything that says this process is lossless just high efficiency. It’s definitely not perpetual motion eventually the system would lose all thermal energy and no longer output any electrical energy. If producing waste heat meant perpetual motion, geothermal would also be classified as perpetual motion, but it isn’t lossless. It seems like it’s essentially a heat pump at a much smaller scale where the ambient temp of the room keeps the graphene’s thermal energy charged in a way. Idk nothing on this seems unintuitive unless they start trying to claim it has massive outputs. I’m guessing this is something that could help power some micro sensors by using heat in the environment but not for anything larger as you’d probably need massive sheets of graphene and they havent really said anything about scaling. Although word of caution I’m only a software engineer not a theoretical physicist, so take my ramblings with a grain of salt and defer to any actual physicists in the comments here haha
You can’t destroy energy though. Where is it going?
Consider a closed system. That energy has to go somewhere. In the geothermal example, it is going into waste heat — heat which cannot be re-harvested because it requires a temperature differential.
If you don’t require a temperature differential, where’s the loss occurring here? How is the “waste” heat non-harvestable? I don’t see how a closed system could ever reach absolute zero.
Well if this works as they say I’d guess this isn’t working without a temperature gradient, just a very small one that is found throughout the molecules in the graphene sheet itself, hence why this needs to be above zero Kelvin and why I’d guess they are only targeting micro/nano sensors to power as they can’t ever scale this beyond the inherent gradient present in graphene. I’m not a physicist so don’t take my word as the gospel but at the same time I don’t see why this is ruffling so many feathers when it clearly can’t scale past these smaller voltages that they are targeting, which seems to hint at this just being a way to take advantage of the natural heat loss on graphene for small powered devices.
If it works then it doesn’t matter how many feathers it ruffles. I had the perpetual motion thought as well, but if it works, it works.