2D Ultrathin Ion‐Selective Membranes With Negatively Charged Interlayer Spacing Enabled by Edge‐Sulfonated Graphene Oxide for Efficient Osmotic Power Generation

ABSTRACT Salinity gradient energy harvesting via reverse electrodialysis holds great potential for sustainable energy development, yet the inefficiency of ion‐selective membranes remains a critical bottleneck. Although 2D material membranes have surpassed the commercial benchmark in microscale tests, their power densities deteriorate drastically with area expansion, presenting a prominent scalability challenge that hinders practical applications. To attain high power density across both small and large test areas, a heterogeneous membrane consisting of an edge‐sulfonated graphene oxide (SGO) ultrathin selective layer and an oxidized micro fibrillated cellulose (OMFC) support layer was proposed. SGO enhances negative surface charge density and provides an expanded interlayer spacing, facilitating rapid and selective ion transport; OMFC enhances the membrane's structural stability and imparts significant negative surface charge density. Under the common test area, SGO‐OMFC membrane achieves a notable power density of 132.7 W·m ⁻² . Furthermore, when the membrane area is increased by a factor of 10,000, the power density remains at 0.74 W·m ⁻² , marking a significant advancement at the square centimeter scale and substantially surpassing the performance of commercial ion‐exchange membranes. This novel heterogeneous membrane design enhances power density while maintaining efficacy across an extensive area, thereby addressing scalability challenges and facilitating potential industrial applications in the future.