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The dependence of performance and stability of a zero-gap CO 2 electrolyzer on the properties of the anion exchange membrane (AEM) is examined. This work firstly assesses the influence of the anolyte when using an Aemion membrane and then shows that when using 10 mM KHCO 3 , a CO 2 electrolyzer using a nextgeneration Aemion + membrane can achieve lower cell voltages and longer lifetimes due to increased water permeation. The impact of lower permselectivity of Aemion + on water transport is also discussed. Using Aemion + , a cell voltage of 3.17 V at 200 mA cm À 2 is achieved at room temperature, with a faradaic efficiency of > 90 %. Stable CO 2 electrolysis at 100 mA cm À 2 is demonstrated for 100 h, but with reduced lifetime at 300 mA cm À 2 . However, the lifetime of the cell at high current densities is shown to be increased by improving water transport characteristics of the AEM and reducing dimensional swelling, as well as by improving cathode design to reduce localized dehydration of the membrane.

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