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

Abstract

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.