Urushi/Nafion Hybrid Membranes for an All-Vanadium Redox Flow Battery

An urushi/Nafion hybrid membrane is prepared via a thermal insitu crosslinking reaction of natural urushiol to reduce the crossover of vanadium ions in an all vanadium redox flow battery (RFB). The ionic channel of the Nafion is blocked by the urushi, a crosslinked natural polymer formed by the polymerization of the adsorbed urushiol. Urushi, which has high chemical robustness in acid solution, is well-formed within the volume of the ion cluster, and the presence of urushi inside the Nafion membrane is confirmed. The permeability and swelling decrease with increasing urushi in the hybrid membrane. The RFB with a hybrid membrane has higher efficiency than the RFB with Nafion. The coulombic and energy efficiencies are 95% and 91%, respectively, for the membrane containing 3.2 wt% of urushi at 11.1 mA cm(-2), suggesting that the urushi in the hybrid membrane can suppress vanadium ion crossover. The chemical and mechanical strengths are maintained in Fenton reagent, which enables long-term use of hybrid membranes to operate the RFB in strong acid solutions. These results suggest that the urushi/Nafion membrane with a chemically stable urushi inside the ion channel enables the successful use of all vanadium RFB as an energy storage system.