Understanding the CO₂ reduction reaction anolyte flooding problem in polymer electrolyte type reactor through the cation and water transport properties of ion exchange membranes

Abstract In electrochemical CO 2 reduction reactors, the polymer electrolyte membrane type reactor, known as a zero-gap cell, achieves excellent CO 2 reduction performance and high current density, but the short reactor lifetime due to flooding and salt precipitation at the cathode are serious problems. It is known that flooding and salt precipitation vary greatly depending on the cell operating conditions, but the mechanisms behind these changes are not well understood. We focused on the anion exchange membrane in the reactor and proposed a qualitative model for mass transfer across the membrane in a zero-gap cell. The data for the amounts of metal cations and water molecules passing through the membrane is measured using a homemade H-type cell. We qualitatively explained the conditions for the excess transportation of water molecules and cations from the anode to the cathode of the membrane using these data. We also proposed the conditions expecting to stop these transports.