Scientists sequester CO2, create electricity

US RESEARCHERS are developing an oxygen-assisted aluminium/CO₂ power cell that uses electrochemical reactions to both sequester CO₂ and produce electricity.

The Cornell University team’s proposed cell would use aluminium as the anode and mixed streams of carbon dioxide and oxygen as the active ingredients as the cathode. The electrochemical reactions between the anode and the cathode would sequester the CO₂ and convert it into carbon-rich compounds while also producing electricity and a valuable oxalate by-product.

In current carbon capture methods, the gas is captured in liquids or solids, which are then heated or depressurised to release the CO₂. The concentrated gas must then be compressed and transported to industries able to reuse it, or sequestered underground. The team says its power cell may represent a paradigm shift to capturing CO₂ and converting it into useful products, while generating electricity.

Lynden Archer, a professor of chemical and biomolecular engineering at Cornell, 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 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.”

In the lab, the electrochemical cell generated 13 Ah/g of porous carbon (as the cathode) at a discharge potential of around 1.4 V. The energy produced by the cell is comparable to that produced by the highest energy-density battery systems.

The team say the other key finding in the experiments was the generation of superoxide intermediates, which are formed when oxygen is reduced at the cathode. The superoxide reacts with the normally inert CO₂, forming a carbon-carbon oxalate that is widely used in industries including pharmaceutical, fibres, and metal smelting. Archer noted that the configuration of the electrochemical cell will depend on the product being made from the oxalate.

Wajdi Al Sadat, a doctoral student on the team, said this technology is not limited to power-plant applications.

'It fits really well with onboard capture in vehicles. 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, Al Sadat commented, as it is abundant, safer to use than other high-energy density metals and cheaper than lithium or sodium, while having comparable energy density to lithium. He added that many aluminium plants are already incorporating power-generation facilities of some sort into operations, so this technology could assist in both power generation and reducing carbon emissions.

The next step for the team will be to address the performance of the electrochemical systems and will look to improve the electrolyte – the liquid connecting the anode and cathode – as it is very sensitive to water.

Science Advances, DOI: 10.1126/sciadv.1600968