Researchers at Rensselaer Polytechnic Institute have developed a new method to harvest energy from flowing water. This discovery aims to hasten the creation of self-powered microsensors for more accurate and cost-efficient oil exploration. Nanoengineered Graphene coating harvests energy from flowing water which powers microsensors used to detect underground oil and gas. The research team demonstrated the creation of 85 nanowatts of power from a sheet of graphene measuring .03 millimeters by .015 millimeters.
Nanoletters - Harvesting Energy from Water Flow over Graphene
This amount of energy should be sufficient to power tiny sensors that are introduced into water or other fluids and pumped down into a potential oil well, Koratkar said. 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. As long as water is flowing over the graphene-coated devices, they should be able to provide a reliable source of power. This power is necessary for the sensors to relay collected data and information back to the surface.
“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,” said Koratkar, professor in the Department of Mechanical, Aerospace, and Nuclear Engineering and the Department of Materials Science and Engineering in the Rensselaer School of Engineering. “While a similar effect has been observed for carbon nanotubes, this is the first such study with graphene. The energy-harvesting capability 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.”
Water flow over carbon nanotubes has been shown to generate an induced voltage in the flow direction due to coupling of ions present in water with free charge carriers in the nanotubes. However, the induced voltages are typically of the order of a few millivolts, too small for significant power generation. Here we perform tests involving water flow with various molarities of hydrochloric acid (HCl) over few-layered graphene and report order of magnitude higher induced voltages for graphene as compared to nanotubes. The power generated by the flow of 0.6 M HCl solution at 0.01 m/sec was measured to be 85 nW for a 30 × 16 μm size graphene film, which equates to a power per unit area of 175 W/m2. Molecular dynamics simulations indicate that the power generation is primarily caused by a net drift velocity of adsorbed Cl– ions on the continuous graphene film surface.
Hydrocarbon exploration is an expensive process that involves drilling deep down in the earth to detect the presence of oil or natural gas. Koratkar 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. 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 the 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 team’s discovery is a potential solution for a key challenge to realizing these autonomous microsensors, 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.
“We’ll wrap the graphene coating around the sensor, and it will act as a ‘smart skin’ that serves as a nanofluidic power generator,” Koratkar said.
Looking at potential future applications of this new technology, Koratkar said he could envision self-powered microrobots or microsubmarines. Another possibility is harvesting power from a graphene coating on the underside of a boat.
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