As the hydration diameter of cations intercalated in Ti₃C₂T _x MXene membranes increases, the interlayer spacing expands, widening the nanochannels. This enlargement enhances slip length, thereby boosting water flux, while also increasing ion permeation.

Ti₃C₂T _x MXene membranes have attracted considerable interest due to their exceptional water transport properties, yet the role of cation intercalation on governing transport remains poorly understood. In this experimental and theoretical study, it shows how intercalation with K⁺, Na⁺, Li⁺, Ca²⁺, and Mg²⁺ modulates both the nanochannel architecture and water flux of Ti₃C₂T _x membranes. Unlike in graphene oxide analogs, cations with larger hydration diameters in Ti₃C₂T _x expand the interlayer spacing, widening flow channels, enhancing slip length of these nanochannels, and boosting water flux from 31.45 to 61.86 L m ⁻² h⁻¹. To overcome intrinsically poor adhesion of Ti₃C₂T _x to polymeric supports, this study incorporates a thin polyvinyl-alcohol interlayer, which substantially enhances mechanical robustness and structural integrity. Together, these findings elucidate how cation hydration controls water transport and offer a flexible strategy for tailoring MXene membrane performance.