Figure shows the evolution of H2O content as a function of time. Immediately after the current step there is always a noticeable drop in the H2O intensity, which can be attributed to a number of parameters. These parameters include the consumption of H2O by the cathodic reaction, the production of H2 and other gasses that remove the H2O, the electroosmosis of H2O due to anion movement towards the anode, the drier conditions at the anode side due to the OER, etc. A detailed discussion is presented in Supplementary Note 4. After this sudden intensity drop, a strong relation is shown between the Cs + and H2O content as a function of time. This correlation is attributed to the electroosmotic drag of H2O, i.e., when Cs + migrates across the AEM under the driving force of electric field, it tends to drag H2O along with it. The extent to which cations transfer H2O molecules depends on their hydration number and will vary for each cationic type, and previous studies have shown that the hydration number of Cs + is ~2. Causes of GDL Flooding During CO2 Electrolysis