Graphene sheet, in blue, next to gold contacts (image courtesy of Rensselaer Polytechnic Institute)
To see how nanomaterials could be used to generate electricity from water flow, Rensselaer Polytechnic Institute professor Nikhil Koratkar has discovered the surprising potential of graphene as a generator. Using a sheet of graphene measuring 0.15mm by 0.03mm, Koratkar and his team observed the generation of 85 nano-watts. As water passes over the 1 atom thick graphene layer, chloride ions in the water stick the surface. As water continues to flow over the graphene, friction between the water and the absorbed chloride ions force the ions to drift in the direction of flow. These ion forces cause the free charges in the graphene to flow along the water's direction causing an internal current in the coating.
The immediate application for the discovery would be in hydrocarbon exploration. Koratkar stated that oil and gas companies want to increase the ease and efficiency of the search by using micro and nano-scale sensors sent into drilled wells to not only sense where they drilled but also laterally. The sensors would travel through underground water sources to help uncover hidden pockets of oil and gas in the crevices of the earth. The sensors would be coated with a graphene layer, and as they travel through water they could generate their operating current.
Kptatkar explained, "It’s impossible to power these microsensors with conventional batteries, as the sensors are just too small. So we created a graphene coating that allows us to capture energy from the movement of water over the sensors... We’ll wrap the graphene coating around the sensor, and it will act as a ‘smart skin’ that serves as a nanofluidic power generator."
Further ideas for use, Koratkar mentioned self powered microbots and mico submarines, as well as coating the undersides of boats with a graphene layer. Keep in mind, 1 square millimeter of graphene could produce ~19 micro-watts in the presence of chlorine ions. How many square millimeters can you place on a aircraft carrier haul?
[The research team also tested carbon nanotubes in a similar fashion. The energy produced paled in comparison to graphene's output.]