The journal paper is linked in the article if you want to read it. For low-voltage devices it seems reasonable to me.
Fluctuation-induced current from freestanding graphene https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.0...
Fluctuation-induced current from freestanding graphene https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.0...
But it sounds to me from the abstract like the result is not significantly different from the thermal noise voltage on a resistor? I don't expect that they would be able to extract any work from the system, unless there is a temperature difference somewhere.