Dual Polyamide Thin‐Film Composite Membrane With Multiscale Hetero‐Channels and Mosaic Charge Architecture for Boosting Ion Transport and Osmotic Energy Conversion

Abstract

ABSTRACT Asymmetric ion‐selective membranes show promise for efficient osmotic energy harvesting. Most current asymmetric membranes adopt a bipolar structure to mitigate concentration polarization. However, this approach usually increases transport resistance and compromises ion selectivity. To address these, we rationally designed a dual polyamide thin‐film composite (dPA TFC) membrane via sequential interfacial polymerization (IP). The membrane is composed of two distinct polyamide (PA) layers in situ formed on a macroporous substrate. Through a surfactant‐assisted IP process, an ultrathin inner PA layer with a uniform and negatively charged 3D pore structure was obtained, delivering both high ion selectivity and permeability. Subsequently, a loose outer PA layer featuring a mosaic charge architecture was constructed using protonated porphyrin as a building block. This layer promotes significant unidirectional ion transport and effectively suppresses concentration polarization, while maintaining a high cation selectivity of 0.962. Additionally, the membrane exhibits photo‐responsive behavior, enabling photo‐enhanced osmotic energy conversion and antibacterial activity. As a result, the dPA TFC membrane achieves a high osmotic power density of 13.2 W m −2 under light irradiation. This work provides a design paradigm that overcomes the conventional permeability‐selectivity trade‐off while simultaneously balancing ion concentration polarization suppression with high selectivity, thereby advancing the development of osmotic energy conversion systems.