<Researchers at Rensselaer Polytechnic Institute have developed a method to produce energy from flowing water using graphene coating. This can be used to create self-powered micro sensors for more accurate and cost-efficient oil exploration.
Researchers coated surfaces with the nanomaterial graphene and made water to flow over it and found that small power can be generated. By this way they created 85 nanowatts of power from a graphene sheet of size .03 by .015 mm. As long as water is flowing over the graphene-coated devices, they should be able to provide a reliable source of power. This has been specifically investigated for oil exploration purposes.
Purpose
Hydrocarbon exploration is an expensive process that involves drilling deep down in the earth to detect the presence of oil or natural gas. Researchers said oil and gas companies would like to augment this process by sending out large numbers of microscale or nanoscale sensors into new and existing drill wells. Theenergy generated should be sufficient to power tiny sensors that are introduced into water or other fluids and pumped down into a potential oil well. As the injected water moves through naturally occurring cracks and crevices deep in the earth, the devices detect the presence of hydrocarbons and can help uncover hidden pockets of oil and natural gas. This power is sufficient for the sensors to collect and relay collected data and information over to the data station.
It is impossible to power these micro sensors with conventional batteries, as the sensors are just too small. Hence a graphene coating was created that allows capture of energy from the movement of water over the sensors.
Even though a similar effect has been observed for carbon nanotubes, the power generating capacity of graphene was at least an order of magnitude superior to nanotubes. Moreover, the advantage of the flexible graphene sheets is that they can be wrapped around almost any geometry or shape.
Working
These sensors would travel laterally through the earth, carried by pressurized water pumped into these wells, and into the network of cracks that exist underneath Earth's surface. Oil companies would no longer be limited to vertical exploration, and the data collected from the sensors would arm these firms with more information for deciding the best locations to drill. The discovery is a potential solution for a key challenge to realizing these autonomous micro sensors, which will need to be self-powered. By covering the microsensors with a graphene coating, the sensors can harvest energy as water flows over the coating. The graphene coating is wrapped around the sensor, and it will act as a 'smart skin' that serves as a nanofluidic power generator.
Graphene coating
Graphene is a single-atom-thick sheet of carbon atoms, which are arranged like a chain-link fence. For this study, graphene was grown by chemical vapor deposition on a copper substrate and transferred onto silicon dioxide.
Researchers used molecular dynamics simulations to better understand the physics of this phenomenon. They discovered that chloride ions present in the water stick to the surface of graphene. As water flows over the graphene, the friction force between the water flow and the layer of adsorbed chloride ions causes the ions to drift along the flow direction. The motion of these ions drags the free charges present in graphene along the flow direction creating an internal current. This means the graphene coating requires ions to be present in water to function properly. Therefore, oil exploration companies would need to add chemicals to the water that is injected into the well.
Potential future applications of this new technology, is self-powered micro robots or micro submarines and harvesting power from a graphene coating on the underside of a boat