Development of Membranes and Separators to Inhibit Cross-Shuttling of Sulfur in Polysulfide-Based Redox Flow Batteries: A Review

The global rapid transition from fossil fuels to renewable energy resources necessitates the implementation of long-duration energy storage technologies owing to the intermittent nature of renewable energy sources. Therefore, the deployment of grid-scale energy storage systems is inevitable. Sulfur-based batteries can be exploited as excellent energy storage devices owing to their intrinsic safety, low cost of raw materials, low risk of environmental hazards, and highest theoretical capacities (gravimetric: 2600 Wh/kg and volumetric: 2800 Wh/L). However, sulfur-based batteries exhibit certain scientific limitations, such as polysulfide crossover, which causes rapid capacity decay and low Coulombic efficiency, thereby hindering their implementation at a commercial scale. In this review article, we focus on the latest research developments between 2012-2023 to improve the separators/membranes and overcome the shuttle effect associated with them. Various categories of ion exchange membranes (IEMs) used in redox batteries, particularly polysulfide redox flow batteries and lithium-sulfur batteries, are discussed in detail. Furthermore, advances in IEM constituents are summarized to gain insights into different fundamental strategies for attaining targeted characteristics, and a critical analysis is proposed to highlight their efficiency in mitigating sulfur cross-shuttling issues. Finally, future prospects and recommendations are suggested for future research toward the fabrication of more effective membranes with desired properties.

Cation Exchange Membranes and Process Optimizations in Electrodialysis for Selective Metal Separation: A Review

The selective separation of metal species from various sources is highly desirable in applications such as hydrometallurgy, water treatment, and energy production but also challenging. Monovalent cation exchange membranes (CEMs) show a great potential to selectively separate one metal ion over others of the same or different valences from various effluents in electrodialysis. Selectivity among metal cations is influenced by both the inherent properties of membranes and the design and operating conditions of the electrodialysis process. The research progress and recent advances in membrane development and the implication of the electrodialysis systems on counter-ion selectivity are extensively reviewed in this work, focusing on both structure-property relationships of CEM materials and influences of process conditions and mass transport characteristics of target ions. Key membrane properties, such as charge density, water uptake, and polymer morphology, and strategies for enhancing ion selectivity are discussed. The implications of the boundary layer at the membrane surface are elucidated, where differences in the mass transport of ions at interfaces can be exploited to manipulate the transport ratio of competing counter-ions. Based on the progress, possible future R&D directions are also proposed.

A novel proton exchange membrane derived from trisulfonated poly(arylene ether phosphine oxide) containing diphenyl ether moieties

A series of novel trisulfonated phosphine oxide polymers (tsPEPO-x) with different sulfonation degrees were prepared by intermolecular polymerization of trisulfonated phosphine monomer and 4,4′-dihydroxydiphenyl ether. The properties of these membranes were investigated in detail. The results showed that these membranes, especially those with high sulfonation degree, exhibited excellent overall performance. For example, the conductivity of tsPEPO-120 membrane reaches 0.093 S cm−1 at 80°C, which is higher than that (0.087 S cm−1) of Nafion 117. At the same time, the swelling rate is almost equivalent to that (20%) of Nafion 117. Moreover, the membrane also has good oxidation resistance in Fenton’s reagent. The obtained polymers showed good properties. The trisulfonated moieties and diphenyl ether simultaneously played important roles in improving the properties of the polymer.

Sulfonated poly(arylene thioether phosphine oxide)s (sPTPO) and sPTPO/sulfonated polybenzothiazole blends as proton exchange membranes

Blends of sulfonated poly(arylene thioether phosphine oxide)s and sulfonated polybenzothiazoles exhibited excellent overall properties as proton exchange membranes.

High-performance proton exchange membranes for direct methanol fuel cells based on a SPEEK/polybenzoxazine crosslinked structure

SPEEK/PBa crosslinked membranes with low methanol permeability and high selectivity were prepared as PEM for DMFC applications.

Enhanced performance of poly(ether sulfone) based composite proton exchange membranes with sulfonated polymer brush functionalized graphene oxide

Novel poly(ether sulfone) based composite proton exchange membranes with enhanced performance were prepared by incorporating sulfonated polymer brush functionalized GO.