Acid-humidified CO2 gas input for stable electrochemical CO2 reduction reaction.

(Bi)carbonate salt formation has been widely recognized as a primary factor in poor operational stability of the electrochemical carbon dioxide reduction reaction (CO2RR). We demonstrate that flowing CO2 gas into an acid bubbler-which carries trace amounts of acid vapor into a gas diffusion electrode for silver-catalyzed CO2RR to carbon monoxide (CO)-can prevent salt accumulation. In a 100-square-centimeter, scaled-up CO2RR membrane electrode assembly electrolyzer with single serpentine flow channels, the acid humidification method achieved the 4500 hours of stability milestone at 100 mA cm-2 without compromising the CO faradaic efficiency, whereas a conventional water-humidified CO2 feed only operated stably for ~80 hours. The acid-humidified CO2 approach was extended to bismuth, copper, and zinc catalysts.