Carbon-capture tech converts CO2 to electrical energy

Article By : Tom Fleischman

In current carbon-capture models, the carbon is captured in fluids or solids. Researchers suggest a paradigm shift.

It's inevitable that the human race will leave its carbon footprint on the Earth, and therefore it must continue to find ways to lessen the impact of its fossil fuel consumption. But how?

One approach is carbon capture technologies, which chemically trap carbon dioxide before it is released into the atmosphere. And in a new report published in Science Advances, Cornell researchers have disclosed a novel method for capturing the greenhouse gas and converting it to a useful product–while producing electrical energy.

Lynden Archer, the James A. Friend Family Distinguished Professor of Engineering, and doctoral student Wajdi Al Sadat have developed an oxygen-assisted aluminium/carbon dioxide power cell that uses electrochemical reactions to both sequester the carbon dioxide and produce electricity.

The group’s proposed cell would use aluminium 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 by-product.

__Figure 1:__ *(Source: Clive Howard/Cornell Marketing Group)*

In most current carbon-capture models, the carbon is captured in fluids or solids, which are then heated or depressurised 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 CO2 capture technology in electric power plants is that the regeneration of the fluids used for capturing CO2 utilise as much as 25% of the energy output of the plant. This seriously limits commercial viability of such technology. Additionally, the captured CO2 must be transported to sites where it can be sequestered or reused, which requires new infrastructure.”

The group reported that their electrochemical cell generated 13A hours per gram of porous carbon (as the cathode) at a discharge potential of around 1.4V. 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 said, is in the generation of superoxide intermediates, which are formed when the O2 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, fibre and metal smelting.

“A process able to convert CO2 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 synthesise 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 on-board carbon capture vehicles at Saudi Aramco, said this technology in not limited to power-plant applications. “It fits really well with on-board 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 aluminium 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 aluminium 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.

There's just one drawback: The electrolyte connecting the anode to the cathode is extremely sensitive to water. On-going work is addressing the performance of electrochemical systems and the use of electrolytes that are less water-sensitive.