Researchers convert carbon dioxide, create electricity
CORNELL
UNIVERSITY
While the human race will always leave its carbon
footprint on the Earth, it must continue to find ways to lessen the impact of
its fossil fuel consumption.
"Carbon capture"
technologies - chemically trapping carbon dioxide before it is released into
the atmosphere - is one approach.
In a recent study, Cornell University
researchers disclose a novel method for capturing the greenhouse gas and
converting it to a useful product - while producing electrical energy.
Their paper, "The
O2-assisted Al/CO2 electrochemical cell: A system for CO2 capture/conversion
and electric power generation," was published July 20 in Science
Advances.
The group's proposed cell
would use aluminum as the anode and mixed streams of carbon dioxide and oxygen
as the active ingredients of the cathode. The electrochemical reactions between
the anode and the cathode would sequester the carbon dioxide into carbon-rich
compounds while also producing electricity and a valuable oxalate as a byproduct.
In most current
carbon-capture models, the carbon is captured in fluids or solids, which are
then heated or depressurized to release the carbon dioxide. The concentrated
gas must then be compressed and transported to industries able to reuse it, or
sequestered underground. The findings in the study represent a possible
paradigm shift, Archer said.
"The fact that we've
designed a carbon capture technology that also generates electricity is, in and
of itself, important," he said.
"One of the roadblocks to adopting
current carbon dioxide capture technology in electric power plants is that the
regeneration of the fluids used for capturing carbon dioxide utilize as much as
25 percent of the energy output of the plant. This seriously limits commercial
viability of such technology. Additionally, the captured carbon dioxide must be
transported to sites where it can be sequestered or reused, which requires new
infrastructure."
The group reported that
their electrochemical cell generated 13 ampere hours per gram of porous carbon
(as the cathode) at a discharge potential of around 1.4 volts. The energy
produced by the cell is comparable to that produced by the highest
energy-density battery systems.
Another key aspect of
their findings, Archer says, is in the generation of superoxide intermediates,
which are formed when the dioxide is reduced at the cathode. The superoxide
reacts with the normally inert carbon dioxide, forming a carbon-carbon oxalate
that is widely used in many industries, including pharmaceutical, fiber and
metal smelting.
"A process able to
convert carbon dioxide into a more reactive molecule such as an oxalate that
contains two carbons opens up a cascade of reaction processes that can be used
to synthesize a variety of products," Archer said, noting that the configuration
of the electrochemical cell will be dependent on the product one chooses to
make from the oxalate.
Al Sadat, who worked on
onboard carbon capture vehicles at Saudi Aramco, said this technology in not
limited to power-plant applications. "It fits really well with onboard
capture in vehicles," he said, "especially if you think of an
internal combustion engine and an auxiliary system that relies on electrical
power."
He said aluminum is the
perfect anode for this cell, as it is plentiful, safer than other high-energy
density metals and lower in cost than other potential materials (lithium,
sodium) while having comparable energy density to lithium.
He added that many
aluminum plants are already incorporating some sort of power-generation
facility into their operations, so this technology could assist in both power
generation and reducing carbon emissions.
A current drawback of this
technology is that the electrolyte - the liquid connecting the anode to the
cathode - is extremely sensitive to water. Ongoing work is addressing the
performance of electrochemical systems and the use of electrolytes that are
less water-sensitive.
###
This work made use of the
Cornell Center for Materials Research, which is supported by the National
Science Foundation. Funding came from a grant from the King Abdullah University
of Science and Technology Global Research Partnership program.
