High-performance ionic covalently modified polyamide acid membrane for osmotic energy conversion

Nanofluidic membranes exhibit considerable promise for osmotic energy harvesting. However, a persistent challenge lies in engineering porous structures that simultaneously facilitate rapid, high-flux ion transport while maintaining high selectivity and robust mechanical strength. Herein, we introduce a strategy that leverages the coordination interaction between Cu²⁺ ions and the carboxyl groups on polyamide acid (PAA) molecular chains to transform an initially dense PAA membrane into one with a uniform nanoporous architecture. The resultant PAA-Cu composite membrane achieves an exceptionally high-power density of 187 W/m² in osmosis energy conversion tests with a 50-fold KCl concentration gradient (0.5 M/0.01 M), a performance that substantially surpasses other state-of-the-art materials. This superior performance is attributed to the nanoporous network created by copper ion coordination, which concurrently maintains high ion selectivity while significantly enhancing the overall ion transport flux. Notably, the PAA-Cu membrane was fabricated at a large scale (up to 390 cm²) and exhibited a high tensile strength of 83 MPa, demonstrating the mechanical robustness required for practical applications. This strategy of synergistically optimizing the membrane's pore structure and surface chemistry through metal coordination offers a promising new avenue for designing next-generation nanofluidic membranes for osmotic energy harvesting.