Pore-filled anion-exchange membranes for non-aqueous redox flow batteries with dual-metal-complex redox shuttles

• Pore-filled anion-exchange membranes were prepared for non-aqueous RFB application.
• The ion transport characteristics in aqueous and non-aqueous media were investigated.
• Novel Fe/Ni dual-metal complex redox electrolyte was employed for this work.
• The low membrane swellability was believed to mitigate the crossover of metal cations.
• A respectable energy efficiency was achieved by using the pore-filled membranes.

Pore-filled anion-exchange membranes (PFAEMs) were synthesized using thin porous polymer substrates for non-aqueous redox flow battery (RFB) applications. The PFAEMs which have a thickness of about 25 μm exhibited high ion conductivity and selectivity in both aqueous and non-aqueous media. In addition, they showed excellent mechanical properties as well as dimensional stability in a non-aqueous environment. The non-aqueous RFB experiments utilizing novel Fe/Ni dual-metal complex redox electrolyte resulted in the respectable energy efficiencies (i.e. 87.3% and 77.2% in non-flowing and flowing cells, respectively) much higher than those of previous papers where other non-aqueous redox electrolytes were used. The PFAEMs showed much better ion selectivity in non-aqueous medium compared to that of the commercial membrane due to the relatively low swellability. The results demonstrated that the charge–discharge performances were largely enhanced by the mitigated crossover of metal complex as well as the low mass transport resistance through the membrane.

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