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).
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.
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 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?