Carbonate Ion Crossover in Zero-Gap, KOH Anolyte CO₂ Electrolysis

A room-temperature zero-gap, KOH anolyte CO₂ electrolyzer demonstrating 40% energetic conversion efficiency (EE) for CO₂ to CO using AEMION anion-exchange membranes is achieved at an industrially relevant current density of 200 mA cm⁻². The concentration and volume of the anolyte are found to be critical to the determination of EE as carbonate ion crossover is shown to cause a significant increase in ECell during continuous operation. Using thicker and/or lower ion-exchange capacity variant membranes results in an approximately 20% reduction in carbonate ion crossover, which is critical for the economic viability of direct CO₂ electrolysis systems. It is proposed that future membrane designs must reduce carbonate crossover without compromising the electrolyzer efficiency and stability.