Acidic Electroreduction of CO2 to Multi-Carbon Products with CO2 Recovery and Recycling from Carbonate

Gas-fed flow cells can facilitate high-rate electrochemical CO2 reduction (CO2R). However, under alkaline and neutral conditions, CO2 is lost through reaction with hydroxide ions to form (bi)­carbonate. In acidic solutions, although (bi)­carbonate is still formed due to increased pH at the electrode, the low bulk pH of the electrolyte solution can regenerate CO2 which is then available for re-reaction or releasethis therefore avoids permanent CO2 loss. Here, we show how CO2 is converted and released in a bipolar-membrane-based gas-fed flow cell for CO2R to multicarbon products (C2+ faradaic efficiency >60%) employing an acidic catholyte. Under the highest conversion conditions, we showed that almost exclusively CO2R products were obtained at one outlet, while, at the second outlet, a nearly product-free stream of CO2 was obtained due to the continuous internal regeneration from (bi)­carbonate. The system presented here avoids permanent reactant loss through the straightforward recovery and recycling of CO2 to improve the overall CO2 utilization.