It sounds like you have basically given a formulation of Maxwell’s Demon https://en.wikipedia.org/wiki/Maxwell%27s_demon

“All you have to do is harvest the hottest/fastest molecules” pretty much describes exactly what Maxwell’s Daemon is.

Now, you can see from the Wikipedia page that there is at least some debate about the topic. But, I think that generally, most physicists think that Maxwell’s Demon would violate the 2nd law, and that the 2nd law is a real limitation.

It certainly sounds like this device would violate the “metaphysics” definition of the 2nd law, “entropy always increases”. Because it sounds like it’s harvesting energy from heat for “free” (not actually energy from nothing, not violating conservation, but free in that you are not paying for the loss of entropy by increasing entropy somewhere else, which is typically “required”).

I am not a physicist, and in my layman’s understanding, I have always felt that the 2nd law seemed fishy. A lot of other people do, too. It’s called “a scientific law”, but it feels more like a philosophical “principle”. It feels different than, for example, “the law of gravity”.

But, this invention, if it is not a hoax or error, sounds world changing. 94 nW/cm2 means a milliwat for 2 square inches. That’s already usable amounts of power for tiny devices. Can you roll up a couple square meters of this stuff into something like a capacitor and get a usable “free” AA battery?

Is heat about to be free energy? No more problems with global warming? Are our refrigerators and air conditioners soon going to be a source of energy rather than a sink?

If this claim is true, then this is world changing technology available to anyone with pretty basic thin film technology…. And there are YouTubers who will be replicating this soon. Let alone real fabrication labs.

You can see why it’s reasonable to be skeptical…

Organic thermoelectric device can harvest energy at room temperature