Oxygen-Resistant CO 2 Reduction Enabled by Electrolysis of Liquid Feedstocks.

Electrolytic CO 2 reduction fails in the presence of O 2 . This failure occurs because the reduction of O 2 is thermodynamically favored over the reduction of CO 2 . Consequently, O 2 must be removed from the CO 2 feed prior to entering an electrolyzer, which is expensive. Here, we show that the use of liquid bicarbonate feedstocks (e.g., aqueous 3.0 M KHCO 3 ), rather than gaseous CO 2 feedstocks, enables efficient and selective CO 2 reduction without additional procedures for removing O 2 . This effect is made possible because liquid bicarbonate solutions, which serve as a liquid CO 2 carrier, deliver high concentrations of captured CO 2 to the cathode, while the low solubility of O 2 in aqueous media maintains a low O 2 concentration at the same cathode surface. Consequently, electrolyzers fed with liquid bicarbonate feedstocks create an environment at the cathode that favors the reduction of CO 2 over O 2 . We validate this claim by electrochemically converting CO 2 into CO with reaction selectivities of 65% at 100 mA cm -2 using a 3.0 M KHCO 3 solution bubbled with 100% CO 2 or 100% O 2 . Similar experiments performed with a gaseous CO 2 feedstock showed that merely 0.5% of O 2 in the feedstock reduced CO selectivity by >90% after 1 h of electrolysis. Our findings demonstrate that a liquid bicarbonate feedstock enables efficient CO 2 reduction without the need for expensive O 2 removal steps.