Ultrahigh Proton/Vanadium Selective and Durable Nafion/TiZrO4 Composite Membrane for High-Performance All-Vanadium Redox Flow Batteries

A single-phase TiZrO4 nanotube (TiZrO4NT)-incorporated Nafion composite membrane with ultrahigh ion selectivity is designed and fabricated for vanadium redox flow batteries (VFBs). A single cell of the VFB using the potential Nafion/TiZrO4NT composite membrane shows high-capacity retention, low self-discharge rate, and high cycling efficiency. Furthermore, an excellent proton conductivity of 75.9 mS cm–1 at room temperature and 23-fold higher H+/VO2+ selectivity (3.61 × 106 S min cm–3) are obtained for the Nafion/TiZrO4NT composite membrane compared with a state-of-the-art Nafion-212 membrane (55.4 mS cm–1 and 0.168 × 106 S min cm–3). Subsequently, a high VFB performance is achieved with 1.7-fold higher discharge capacity and impressive cycling Coulombic efficiency (CE, 99.8%), voltage efficiency (VE, 84.1%), and energy efficiency (EE, 83.9%) using the Nafion/TiZrO4NT composite membrane than those of the Nafion-212 membrane (CE, 89.9%; VE, 81.2%; and EE, 72.9%). Moreover, the low area resistance of the membrane, high-rate capability, excellent battery durability of 300 charge–discharge cycles, and high self-discharge time ensure the incorporation of the TiZrO4NT filler into the Nafion matrix and improve the selectivity of the fabricated Nafion/TiZrO4NT composite membrane. Consequently, the Nafion/TiZrO4NT composite membrane with ultrahigh ion-selectivity and superior battery performance is considered a potential candidate for high-performance VFBs.