Sustainable Nafion–Cellulose Composite Membrane: Role of Biomass-Derived Cellulose Loading in Suppression of Polysulfide Shuttling for Redox Flow Batteries

The cross-shuttling of polysulfide ions in bromine/polysulfide-based redox flow batteries (RFBs) is one of the major challenges that hinder their overall performance. Herein, we utilized cellulose extracted from waste date palm trees (DPT) and Nafion to fabricate an in-house membrane that contributes to mitigating this problem. A series of Nafion membranes with cellulose ratios of 5, 10, 20, and 30 wt% were fabricated and labeled CNF5, CNF10, CNF20, and CNF30, respectively. The CNF20 displayed promising thickness (∼77 µm) and mechanical stability, and as a result, it was investigated further and compared with the commercial Nafion 117 membrane. CNF20 exhibited an ion exchange capacity of 1.35 meq/g, water uptake of 39% and ionic conductivity of 0.090 S/cm. Both membranes exhibited a charge capacity of approximately 555.5 mAh/L. However, CNF20 retained 99.9% of its capacity, as compared to 93.7% for Nafion 117, after 100 cycles. The charge capacity decay and discharge capacity decay for CNF20 were 18 times and 120.6 times lower, respectively, than for the Nafion 117 membrane. The CNF20 showed energy efficiency of 31.3% whereas Nafion 117 exhibited 23.2% over 100 cycles. The cost analysis for CNF20 resulted in a 57.7% reduction as compared to the commercial price of Nafion 117. These results position CNF20 as a cost-effective, sustainable, and eco-friendly alternative compared to a membrane composed solely of Nafion 117.