Ion-conducting membranes have received increasing attention due to their wide applications in fuel cells, flow batteries, electrodialysis, electrolyzers, sensors, actuators, water purifications, etc. They usually consist of a certain number of ionic groups tethered to the polymeric chains. The ionic groups are acidic groups such as sulfonic acid and carboxylic acid groups for cation exchange membranes and basic groups such as quaternary ammonium groups for anion exchange membranes. When both acidic and basic groups are present, amphoteric ion exchange membranes can be formed. The ionic groups are accountable for the ion conductivity, while the polymer chains are accountable for the mechanical properties, chemical stability, thermal stability, dimensional stability, and cost of the membranes. The membranes can be homogeneous and heterogeneous. The polymer chains can be linear or branched, crosslinked or non-crosslinked, with one component or different components. The different components can be randomly copolymerized, block copolymerized, or grafted. The development of ion-conducting membranes is an exciting research area, which involves almost every aspect of polymer science.

Ion conductivity and chemical stability are two key properties of ion-conducting membranes. The mechanical properties, thermal properties, dimensional stability, and cost are important for the practical application of ion-conducting membranes. Lots of works have been devoted to enhancing the membrane properties by chemical or physical methods. There are currently many challenges in this research field. Firstly, the design of high-performance membranes is based on new monomer structures, new segment arrangements, new synthesis strategies, new membrane preparation methods, new composition, and hybridization protocols. Secondly, the investigation of the structure-property relationship in different polymer systems and the use of the relationship in the optimization of the membrane performance for different applications. Thirdly, the theoretical understanding of the membrane processes. Finally, the exploration of new ion-conducting mechanisms.

The aim of this Special Issue is to highlight the recent progress and fundamental aspects of the synthesis, characterization, properties, and applications of ion-conducting membranes. Research at the cutting-edge of different subareas will be selected to initiate in-depth discussions from scientists worldwide. Original research and review articles are welcome.

Potential topics include but are not limited to the following:

• Synthesis of sulfonated polymers for proton exchange membranes
• Modification of sulfonated polymers for proton exchange membranes
• Synthesis of quaternized polymers for anion exchange membranes
• Modification of quaternized polymers for anion exchange membranes
• Synthesis of amphoteric polymers for amphoteric ion exchange membranes
• Modification of amphoteric polymers for amphoteric ion exchange membranes
• Synthesis and modification of other ionic polymers
• Understanding the structure-property relationship of ion-conducting membranes
• New characterization techniques for ion-conducting membranes
• New applications for ion-conducting membranes
• Optimization of the ion-conducting membrane-based device performance
• Modelling of membrane processes