The energy has to be coming from something other than the random thermal motions. This probably amounts to a microscopic version of those old watches that you wind by shaking them.
That’s what I suspect, for instance ambient sound (phonon) energy. ( perhaps from nearby bullhorns announcing preposterous claims of repealing thermodynamics). They say in the blurb graphene mysteriously converts thermal noise to usable frequency vibrations but it more just resonates to sound wave inputs, folks.