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Design and fabrication of phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes with high proton conductivity, mechanical property and phosphoric acid retention stability has been a critical challenge. In this study, a sulfonated ionic covalent organic framework (SCOF) was in-situ synthesized in the polybenzimidazole matrix. The high-density sulfonic groups and ordered channel structure of SCOF rendered the as-prepared composite membrane high proton conductivity under low phosphoric acid doping level. Additionally, the introduction of SCOF helped to immobilize the phosphoric acid, thus effectively reducing its loss and improving the acid retention stability. The acid-base interaction formed between the sulfonic acid and imidazole groups act as ionic crosslinkers, which significantly enhanced the mechanical-dimensional stability of composite membranes. As a result, the PA-PBI/SCOF composite membrane exhibited a high proton conductivity up to 542.1 mS cm−1 at 80 °C, 100 % RH and 134.1 mS cm−1 at 30 °C, 50 % RH, as well as a high mechanical strength up to 64.0 MPa (PA uptake: 67.47 %). This in-situ synthesis strategy offers a promising new approach to fabricate covalent organic framework-based composite membranes for various applications. [Display omitted] • A sulfonated covalent organic framework (SCOF) was in-situ synthesized in polybenzimidazole matrix to prepare composite membranes. • The as-prepared composite membrane exhibited high mechanical strength, proton conductivity and phosphoric acid retention stability. • The composite membrane showed comparable performance in electrochemical hydrogen compression and proton exchange membrane fuel cell. [ABSTRACT FROM AUTHOR]

Developing effective organic solvent nanofiltration (OSN) membranes to separate molecular solutes from organic solvents is highly desired yet requires a suitable material platform and an in-depth investigation of membrane selectivity. Herein, an oriented ionic covalent organic framework membrane (oi -COM) was fabricated, which features well-ordered channels that are vertically aligned towards the membrane surface and lined with abundant sulfonate groups. Filtration experiments of multifarious organic solvents and solutes with different charges and molecular sizes were conducted. The oi -COM exhibited above 99% rejection for negatively charged dye (Evans blue), much higher than that for positively charged dye with similar molecular size, while maintaining high solvent permeance for ethanol of 63 L m−2 h−1 bar−1. These results demonstrated the significance of electrostatic repulsion effect in membrane selectivity, providing insights for the design of high-performance OSN membranes. Oriented ionic COF nanosheet membranes are fabricated, which demonstrate high organic solvent nanofiltration performance and charge-controlled molecular separation. [Display omitted] • Oriented ionic COF nanosheet membranes were fabricated and applied to organic solvent nanofiltration. • The membranes displayed well-defined, vertically aligned and high-density charged channels. • The membranes exhibited excellent solvent permeance for ethanol of 63 L m−2 h−1 bar−1. • The membranes exhibited <99% rejection of anionic dyes, much higher than cationic dyes. • The effect of electrostatic repulsion on membrane selectivity in organic solvents has been demonstrated. [ABSTRACT FROM AUTHOR]