Electrochemical reduction of carbon dioxide

The electrochemical reduction of carbon dioxide, also known as CO2RR, is a process that converts carbon dioxide (CO₂) to more reduced chemical species using electrical energy. CO2RR can produce diverse compounds including formate, carbon monoxide, methane, ethylene, and ethanol. Provided the process is run using renewable energy and the CO₂ is sourced from flue gas or direct air capture, it could be an efficient form of carbon capture and utilization.

CO₂RR has recently seen significant research and commercial interest, due to its potential to reduce greenhouse gas emissions while creating useful products from waste CO₂. The main challenges are the cost of electricity, competition from established petrochemical-based production methods of these products, and the need to purify the CO₂ before use.

The electrochemical reduction of CO₂ first demonstrated in the 19th century, when carbon dioxide was reduced to carbon monoxide using a zinc cathode. The field saw a surge of interest in the 1980s following the oil embargoes of the 1970s. As of 2021, pilot and demonstration scale carbon dioxide electrochemical reduction is being developed by several companies, including Siemens, Dioxide Materials, Twelve, GIGKarasek, and OCOchem. The techno-economic analysis was recently conducted to assess the key technical gaps and commercial potentials of the carbon dioxide electrolysis technology at near ambient conditions.

CO2RR is performed using an electrolyzer in which CO2 is reduced at the cathode while water is oxidized to oxygen gas (O₂) at the anode. The anode typically also contains a catalyst, the choice of which heavily influences the product: for example, gold and silver tend to produce carbon monoxide, while copper often produces multicarbon compounds like ethylene or ethanol. Alternative electrolyzer setups have also been developed to reduce other forms of CO₂, including carbonates or bicarbonates sourced from CO₂, carbamates sourced from flue gas effluents using alkali or amine-based absorbents like MEA or DEA. While the techno-economics of these systems are not yet feasible, they provide a near net carbon neutral pathway to produce commodity chemicals like ethylene at industrially relavant scales.