Acid-humidified CO 2 gas input for stable electrochemical CO 2 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 (CO 2 RR). We demonstrate that flowing CO 2 gas into an acid bubbler—which carries trace amounts of acid vapor into a gas diffusion electrode for silver-catalyzed CO 2 RR to carbon monoxide (CO)—can prevent salt accumulation. In a 100-square-centimeter, scaled-up CO 2 RR 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 CO 2 feed only operated stably for ~80 hours. The acid-humidified CO 2 approach was extended to bismuth, copper, and zinc catalysts.