I am not ready to disbelieve yet. Graphene is a sheet of carbon rings, cyclohexene or something, that has double bonds between carbon atoms that can move. The chemical symbol for this arrangement is a hexagon with a circle inside to indicate the shared nature of these electrons (which is metal like and unusual for covalent bonded atoms, but they are trapped in their own ring). So you add a conductive medium like water and move the metal across the surface and I could see how this could make alternating current. I would like to witness that. I would be shocked to see a couple watts come out of that, though.