Modulating the Interlayer Spacing of Montmorillonite 2D Nanofluidic Membranes by Cation Intercalation for Osmotic Energy Conversion

2D nanofluidic membranes constructed from naturally abundant clay minerals show great potential for harvesting osmotic energy from salinity gradients between seawater and river water. However, their power generation performance is limited by the tradeoff between ion selectivity and ion flux. Herein, a montmorillonite (MMT) 2D nanofluidic membrane is developed by partially substituting interlayer Na⁺ with the organic cation Ru(bpy)₃²⁺, thereby achieving a nanoscale modulation of interlayer spacing while maintaining its high cation selectivity. The resultant intercalated membranes exhibit a surface-charge-governed ion transport property. Under a 50-fold salinity gradient formed by 0.5/0.01 m KCl, the 2D membrane with an optimized interlayer spacing exhibits a maximum power density of 5.30 Wm⁻², which is potentially boosted to be 10.05 Wm⁻² in a hypersaline solution (0.06/3 m) with the same gradient. This work provides an effective strategy to modulate the interlayer spacing of 2D nanofluidic membranes for enhanced osmotic energy conversion performance.