Comment by dTal
I wouldn't hold your breath on being wrong. A device that converts heat into electricity without a gradient is a perpetual motion machine. Consider what would happen if you popped such a device on one side of a thermoelectric plate, and used its output to power a heater on the other side of the plate. The arrangement would permanently maintain a gradient across the thermoelectric plate - free electricity forever!
Not if it produces less heat than it converts, the rest being lost as ... ah, wait a minute. Well anyway it would only produce as much heat as it converts, so this perpetual cycle couldn't do any useful work. Perpetual useless motion is allowed, isn't it?
Oh, I see it now, you're suggesting that it could just passively create a gradient that could produce power in a more conventional way, like via an engine, until I guess the device kicks in again and re-establishes the gradient (producing more power of its own in the process). Yes. That does sound like impossible free energy.