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.
Rensselaer Professor Nikhil Koratkar, the researchers investigated how the flow
of water over surfaces coated with the nanomaterial graphene could generate
small amounts of electricity. The research team demonstrated the creation of 85
nanowatts of power from a sheet of graphene measuring .03 millimeters by .015
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 says.
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.
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," says
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."
the study, titled "Harvesting Energy from Water Flow over Graphene,"
were published online by the journal Nano Letters, which may
be viewed here.
It is the
first research paper to result from the $1 million grant awarded to Koratkar's
group in March 2010 by the Advanced Energy Consortium.
exploration is an expensive process that involves drilling deep down in the
earth to detect the presence of oil or natural gas. Koratkar says that oil and
gas companies would like to augment this process by sending out large numbers
of microscale or nanoscale sensors into new and existing drilled 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 no longer would 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.
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.
wrap the graphene coating around the sensor, and it will act as a 'smart skin'
that serves as a nanofluidic power generator," Koratkar says.
a single-atom-thick sheet of carbon atoms, which are arranged like a chain-link
fence. For this study, Koratkar's team used graphene that was grown by chemical
vapor deposition on a copper substrate and transferred onto silicon dioxide.
The researchers created an experimental water tunnel apparatus to test the
generation of power as water flows over the graphene at different velocities.
physically demonstrating the ability to generate 85 nanowatts of power from a
small fragment of graphene, the 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.
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. Koratkar indicates that this is an easy,
study, Koratkar's team also tested the energy harvested from water flowing over
a film of carbon nanotubes. However, the energy generation and performance was
far inferior to those attained using graphene, he notes.
potential future applications of this new technology, Koratkar says that he
could envision self-powered microrobots or microsubmarines. Another possibility
is harvesting power from a graphene coating on the underside of a boat.
New Graphene Discovery Could Boost Oil Exploration Efforts
July 25, 2011