Organic Cation Gating Control for Water Management in CO ₂ Membrane Electrode Assembly Electrolyzers

Water management is crucial in low-temperature electrochemical technologies (e.g., fuel cells, water electrolysis, and CO2 electrolysis). Herein, we introduce a real-time adjustable water management strategy for CO2 membrane electrode assembly (MEA) electrolyzers. It exploits the semipermeable nature of alkaline polyelectrolyte (APE) membranes, which selectively allow the passage of OH– and water. By adding a controlled amount of 6-azoniaspiro[5.5]undecane cation ([ASU]+) to the anolyte, we can modulate the osmotic pressure across the APE membrane and create a hydrophobic barrier layer via electric field-driven self-assembly. This allows precise gating control of the transmembrane water transport flux from the anode to the cathode, thereby significantly impacting the cathode CO2 reduction performance. A continuous CO2 electrolysis test further shows that simply switching the anolyte between pure water and [ASU]OH solution enables real-time modulation of the cathode water content and, consequently, the CO2 reduction selectivity, underscoring the simplicity and effectiveness of this approach.