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 CO 2 electrolysis). Herein, we introduce a real-time adjustable water management strategy for CO 2 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 CO 2 reduction performance. A continuous CO 2 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 CO 2 reduction selectivity, underscoring the simplicity and effectiveness of this approach.