Hybrid Membranes Dispersed with Superhydrophilic TiO2 Nanotubes Toward Ultra-Stable and High-Performance Vanadium Redox Flow Batteries

The vanadium redox flow battery (VRFB) is a large-scale energy storage technique and has been regarded as a promising candidate to integrate intermittent renewable energy with the grid. Its long-term stability has so far been limited by the core component, an ion exchange membrane with low ion selectivity. Here a hybrid membrane with superhydrophilic TiO2 nanotubes dispersed in a Nafion matrix is reported. The VRFB single cell with the hybrid membrane exhibits an impressive performance with high coulombic efficiency (CE, approximate to 98.3%) and outstanding energy efficiency (EE, approximate to 84.4%) at 120 mA cm(-2), which is higher than that of the commercial Nafion 212 membrane (CE, approximate to 94.5%; EE, approximate to 79.2%). More importantly, the cell maintains a discharge capacity of approximate to 55.7% after 1400 cycles (over 518 h), in obvious contrast to that of approximate to 20% after only 410 cycles for the one using commercial Nafion 212. This is attributed to the high ion selectivity of the hybrid membrane, because of, 1) the blocked and elongated ion diffusion pathway induced by the dispersed nanotubes and 2) binding and alignment of the sulfonic acid groups on nanotube surface. The high-performance membranes may also find important applications in other fields, such as fuel cells, dialytic batteries, and water treatment.