Confined Ionic‐Liquid‐Mediated Cation Diffusion through Layered Membranes for High‐Performance Osmotic Energy Conversion

Ion‐selective membranes act as the core components in osmotic energy harvesting, but remain with deficiencies such as low ion selectivity and a tendency to swell. 2D nanofluidic membranes as competitive candidates are still subjected to limited mass transport brought by insufficient wetting and poor stability in water. Here, an ionic‐liquid‐infused graphene oxide (GO@IL) membrane with ultrafast ion transport ability is reported, and how the confined ionic liquid mediates selective cation diffusion is revealed. The infusion of ionic liquids endows the 2D membrane with excellent mechanical strength, anti‐swelling properties, and good stability in aqueous electrolytes. Importantly, immiscible ionic liquids also provide a medium, allowing partial dehydration for ultrafast ion transport. Through molecular dynamics simulation and finite element modeling, that GO nanosheets induce ionic liquids to rearrange, bringing in additional space charges, which can be coupled with GO synergistically, is proved. By mixing 0.5/0.01 m NaCl solution, the power density can achieve a record value of ≈6.7 W m−2, outperforming state‐of‐art GO‐based membranes. This work opens up a new route for boosting nanofluidic energy conversion because of the diversity of the ILs and 2D materials. Ion transport in random stacked laminar graphene oxide (GO) membrane suffers from limited mass transport brought by insufficient wetting. The pre‐addition of ionic liquids (ILs) in the layer spacing provides a continuous medium for fast ion transport, greatly solving this problem. Meanwhile, nanoconfinement between the charged GO nanosheets promotes the dissociation of ILs and rearrangement, bringing in additional space charges for the osmotic energy conversion.