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Abstract Efficient energy conversion using ions as carriers necessitates membranes that sustain high permselectivity in high salinity conditions, which presents a significant challenge. This study addresses the issue by manipulating the linkages in covalent-organic-framework membranes, altering the distribution of electrostatic potentials and thereby influencing the short-range interactions between ions and membranes. We show that a charge-neutral covalent-organic-framework membrane with β-ketoenamine linkages achieves record permselectivity in high salinity environments. Additionally, the membrane retains its permselectivity under temperature gradients, providing a method for converting low-grade waste heat into electrical energy. Experiments reveal that with a 3 M KCl solution and a 50 K temperature difference, the membrane generates an output power density of 5.70 W m−2. Furthermore, guided by a short-range ionic screening mechanism, the membrane exhibits adaptable permselectivity, allowing reversible and controllable operations by finely adjusting charge polarity and magnitude on the membrane’s channel surfaces via ion adsorption. Notably, treatment with K3PO4 solutions significantly enhances permselectivity, resulting in a giant output power density of 20.22 W m−2, a 3.6-fold increase over the untreated membrane, setting a benchmark for converting low-grade heat into electrical energy.

Abstract Membrane reactors are known for their efficiency and superior operability compared to traditional batch processes, but their limited diversity poses challenges in meeting various reaction requirements. Herein, we leverage the molecular tunability of covalent organic frameworks (COFs) to broaden their applicability in membrane reactors. Our COF membrane demonstrates an exceptional ability to achieve complete conversion in just 0.63 s at room temperature—a benchmark in efficiency for Knoevenagel condensation. This performance significantly surpasses that of the corresponding homogeneous catalyst and COF powder by factors of 176 and 375 in turnover frequency, respectively. The enhanced concentration of reactants and the rapid removal of generated water within the membrane greatly accelerate the reaction, reducing the apparent activation energy. Consequently, this membrane reactor enables reactions that are unattainable using both COF powders and homogeneous catalysts. Considering the versatility, our findings highlight the substantial promise of COF-based membrane reactors in organic transformations.