The most obvious assumption that could explain a decreased water flux or changes in slip length by cation intercalation is that the cations cause steric hindrance for the transport of water molecules. If that was true, the water flux trend should follow the ionic diameter of the cations. As shown in (SI section 2.3-Steric hindrance) the water transport does not follow this trend. In contrary the K + would cause the largest steric hindrance as they have the largest ionic diameter. However, the water transport for K + is the highest among tested cations. For