Rice Paper Reinforced Sulfonated Poly(ether ether ketone) as Low-Cost Membrane for Vanadium Flow Batteries

Low-cost, highly efficient, and durable membrane is essential for practical application of vanadium flow battery (VFB). Sulfonated poly(ether ether ketone) (SPEEK) membrane is considered as potential candidate to replace the expensive Nafion membrane because of its high proton to vanadium ion selectivity. To overcome the poor mechanical/chemical stability of SPEEK membrane in VFB, a new strategy by using commercial paper (copy paper, rice paper, and filter paper) as the scaffold of SPEEK, and subsequently self-cross-linking the SPEEK through thermal treatment was conducted. The optimized rice paper reinforced SPEEK membrane exhibits superior VFB performances to that of the benchmark Nafion 115 membrane, such as 98.3% vs 92.8% for Coulombic efficiency, 79.5% vs 75.8% for energy efficiency, and 0.13% vs 0.16% for capacity decay per cycle at a high current density of 120 mA cm–2. Besides, S@RP-C6 shows an extremely stable performance in the temperature range of 0–70 °C. Combining the outstanding battery performances with the extremely low cost (estimated at about $10 per m2), the rice paper reinforced SPEEK membrane shows a very good application prospect in VFB.