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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]

[Display omitted] • A hydrogen-bond binding strategy is proposed to fabricate iCOF nanosheets (iCONs) and tannic acid (TA) composite membranes. • TA nanoaggregates were synthesized as hydrogen-bond binders. • Abundant hydrogen-bond interactions enable flexible connection between iCONs. • Highly interconnected hydrogen-bond networks facilitate rapid proton transport. • The membranes showed both enhanced mechanical properties and proton conductivity. Robust and highly conductive proton exchange membrane (PEM) is the unremitting pursuit of numerous electrochemical energy technologies such as fuel cell and the emerging electrochemical hydrogen compression. Ionic covalent organic framework nanosheets (iCONs) with long-range ordered nanochannels and abundant ionic groups show substantial potential as next-generation PEM materials. However, it is challenging to assemble iCONs into membranes with both robustness and flexibility due to the electrostatic repulsion and rigid framework. Herein, we propose a hydrogen-bond binding strategy to fabricate sulfonic iCON (SCON) composite membranes by co-assembling tannic acid (TA) nanoaggregates and SCONs. The abundant and dynamically reversible hydrogen-bond interactions introduced by TA nanoaggregates establish effective linkage between SCONs and allow some restricted movements, endowing membranes with remarkably improved mechanical properties. The stacked SCONs construct long-range ordered nanochannels with well-arranged sulfonic groups in membranes, and the hydrogen-bond networks further facilitate the proton transport through Grotthuss mechanism. Consequently, TA/SCON composite membranes displays significantly enhanced tensile strength of 101.9 MPa, good flexibility and high proton conductivity of 490.1 mS cm−1 at 80 °C and 100 % RH simultaneously. This hydrogen-bond binding strategy offers a promising approach to fabricate robust and highly conductive PEMs for various proton-conducting applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1. Electrochemical hydrogen compression (EHC) can purify and compress hydrogen in one step. • 2. Working principle and module design of EHC are described and summarized. • 3. Developments of advanced proton-conducting membranes for EHC are reviewed. • 4. Challenges, future trends and prospects of EHC are discussed. Electrochemical hydrogen compression (EHC), which can purify and compress hydrogen in one step, has aroused broad interests due to its high efficiency, compact equipment, and quiet operation. Since the concept of EHC was proposed, considerable efforts have been devoted to this field. In this review, several aspects of EHC are comprehensively discussed. Firstly, the working principle of EHC is presented with a focus on the electrode reactions, overpotentials, and performance indicators. Subsequently, the major functions, required properties, common materials and recent progress on the design and development of EHC modules are overviewed. As the key part of EHC, recent advances in proton-conducting membranes are particularly summarized, including polymeric proton exchange membranes, mixed matrix proton exchange membranes, and proton ceramic oxide membranes. The focus is on the chemical structures, proton transfer mechanisms, factors affecting performances, and applications for hydrogen purification and compression. Finally, the challenges, future trends, and prospects associated with each module of EHC are discussed. [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]