Asymmetric Two-Dimensional Nanomembranes for Salinity Gradient Energy Conversion

Salinity gradient energy offers a ubiquitous, renewable power source but remains inhibited by the trade-off between the ion selectivity and permeability of the membrane, which limits the diffusion potential and ionic current, thus restricting the output power. We designed a membrane with millimeter-scale lateral channels with angstrom height and unipolar asymmetry to overcome these constraints. By applying a localized spark reaction to vermiculite films, we engineered a robust monolithic asymmetric architecture with an enhanced ion selectivity (95.1% Na⁺) and rectification ratio (R ≈ 10). In modules of 900 cells (30 devices), these membranes sustained power densities of >5.0 W/m², sufficient to charge smartphones and tablets with minimal performance losses. Our platform addresses long-standing performance and scalability barriers in salinity-gradient energy conversion, providing a pathway toward practical, high-power blue energy devices.