Redox flow batteries (RFBs) are promising candidates for large-scale energy storage thanks to their longevity, relatively low initial cost, and independent scaling of energy and power.1 The membrane plays a crucial role in determining both the efficiency and economic feasibility of RFBs, given its importance in regulating performance. 2 Ideally, the membrane should exhibit high ionic conductivity and selectivity to prevent active species crossover while permitting the passage of supporting electrolyte ions. Additionally, it should be chemically stable, mechanically durable, cost-effective, and capable of withstanding high-power densities. 3 Nowadays, membranes for RFBs only partially satisfy all the above-mentioned characteristics and, in particular, they are affected by the trade-off between ionic conductivity and selectivity.4 Our present work is aimed at developing novel polymeric membranes for acidic electrolytes that involve protons exchange. Nafion-based proton exchange membranes (PEMs) are regarded as the main benchmark for many RFBs because of their high ionic conductivity and high stability in chemically aggressive environments.5 However, disadvantages including the exceptionally high cost and crossover of unwanted species (e.g. Br2/Br- in AQDS/Br2 RFBs) prevent their use for large-scale energy storage. In this context, the experimental work was focused on the chemical post-modification of polyvinylidene fluoride (PVDF), a commercially available thermoplastic fluorinated polymer, by grafting from the styrene monomer via atom transfer radical polymerization (ATRP). The obtained PVD-g-Sty graft copolymers were than subjected to sulfonation reaction, to incorporate –SO3H functional groups on the polystyrene side chains. Different copolymers with tuned mole content of styrene and sulfonated styrene were synthesized and used for the preparation of PEMs by solution casting. The membranes were chemically, thermally and mechanically characterized. Selected membranes were tested in 1W single cell to investigate their electrochemical performance.

Ref.

1. Yuan, X. Z. et al. Int. J. Energy Res. 43, 6599–6638 (2019).

2. MacHado, C. A. et al. ACS Energy Lett. 6, 158–176 (2021).

3. Yuan, J. et al.. J. Power Sources 500, 229983 (2021).

4. Dai, Q. et al. T Nat. Commun. 11, 1–9 (2020).