Membranes for Redox Flow Batteries

Membranes are one critical component in redox flow batteries (RFBs), separating active species and allowing ions transfer. These membranes not only could dominate the cycling performance of RFBs, but also impact the overall system cost as they are usually very expensive due to their complex manufacturing. By adopting an efficient non-solvent phase separation (NIPS) method and a tunable post-sulfonation process, we have successfully used a low-cost industrial-scale plastic, blend of poly[phenylene oxide] and high impact polystyrene, into porous ion exchange membranes tailored to aqueous RFB systems. The fabricated membranes shows durable interconnected mesopores with fine-tuned sulfonation, resulting in low area-specific resistance (ASR) and excellent permeability in both acidic and alkaline electrolytes. Flow cell characterization using either 2,6-dihydroxyanthraquinone (2,6-DHAQ) / K₄Fe(CN)₆ or vanadium salts indicates such membranes can deliver outstanding capacity retention and power density. This work exemplifies the approach of using low-cost plastics into valuable products, representing an exciting and sustainable opportunity for addressing critical challenges for long duration energy storage solutions.