Advanced Nafion hybrid membranes with fast proton transport channels toward high-performance vanadium redox flow battery

The development of high-performance ion exchange membranes to break the trade-off between ion selectivity and conductivity is always a great challenge for the vanadium redox flow battery (VRFB). Herein, a hybrid membrane was successfully prepared via the solution casting method. The UiO-66-SO3H was embedded in Nafion matrix, acting as an effective barrier for vanadium ions to realize enhanced ion selectivity. At the same time, besides the intrinsic proton cluster channels in Nafion, two types of additional proton transport channels formed in the membranes, which further improved the conductivity of the membranes. Consequently, the VRFB with an optimized hybrid membrane exhibited enhanced voltage efficiency (VEs: 91.5-78.4%) and outstanding energy efficiency (EEs: 86.0-76.1%) compared with the one with recasting Nafion membrane (rNf) (VEs: 86.9-69.0%, EEs: 80.3-66.0%) at 80–220 mA cm-2. The efficiency kept stable for 1000 cycles in the long-term cycling tests, and the discharge capacity decay rate of the VRFB with the hybrid membrane is only 0.13% per cycle, which is in obvious contrast to the one with rNf (0.73% per cycle). In addition, the electrolyte utilization rate of the VRFB assembled with the hybrid membrane was much higher than that of the one with rNf.