Leveraging Long-Life Alkaline Redox Flow Batteries Using Durable and High-Hydroxide Exchange N-Bridged Triazine Framework Membranes

Abstract

Fluorine-free organic framework polyelectrolyte membranes showing near frictionless ionic conductivities are gaining cognitive insights. However, the co-precipitation of COFs in the membranes often brings trade-offs to commission long-life electrochemical energy storage solutions. Herein, a durable and ionically miscible dual-ion exchange membrane based on triazine organic framework (TOF) is designed for alkaline redox flow batteries (RFB). Bearing dual ion-exchange architectures, the all-hydrocarbon TOF-based PEMs (sTOF's) surpass fluorinated Nafion in terms of energy efficiency (>80%), energy density, and peak power densities. The fabricated sTOF's evidenced the highest net ion-exchange of >2.1 meq g⁻¹ which encourages electrolyte utilization with ≈100% and offers excellent capacities. Moreover, >97% efficiencies are preserved, and rate capability studies illustrate that, with sTOF-5, the RFB can operate at reduced overpotentials (η ≤200 mV) and can uplift batteries life. The sTOF's supports successful demonstrations of batteries at higher redoxolyte concentrations thereby multiplying the energy densities. The afterlife performance of sTOF-5 revealed efficiencies equivalent to fresh Nafion-117 and surpassed bearing >50% capacity after ≈3000 continuous cycles. With sTOF-5, the cell delivered a peak power (P_max) of 2.3 W which is ≈60% higher than that of Nafion-117 (P_max = 1.45 W).