Review—Electrochemical CO<sub>2</sub> Reduction for CO Production: Comparison of Low- and High-Temperature Electrolysis Technologies
Rainer Küngas
Abstract
Recently, the field of CO 2 electrolysis has experienced rapid scientific and technological progress. This review focuses specifically on the electrochemical conversion of CO 2 into carbon monoxide (CO), an important “building block” for the chemicals industry. CO 2 electrolysis technologies offer potentially carbon-neutral routes for the production of specialty and commodity chemicals. Many different technologies are actively being pursued. Electrochemical CO 2 reduction from aqueous solutions stems from the success of alkaline and polymer electrolyte membrane electrolyzers for water electrolysis and uses performance metrics established within the field of aqueous electrochemistry. High-temperature CO 2 electrolysis systems rely heavily on experience gained from developing molten carbonate and solid oxide fuel cells, where device performance is evaluated using very different parameters, commonly employed in solid-state electrochemistry. In this review, state-of-the-art low-temperature, molten carbonate, and solid oxide electrolyzers for the production of CO are reviewed, followed by a direct comparison of the three technologies using some of the most common figures of merit from each field. Based on the comparison, high-temperature electrolysis of CO 2 in solid oxide electrolysis cells seems to be a particularly attractive method for electrochemical CO production, owing to its high efficiency and proven durability, even at commercially relevant current densities.