Large-scale energy storage technologies play a pivotal role in the global clean energy transition, enabling intermittent renewable energy sources such as solar and wind to serve as feasible replacements for fossil fuels. The vanadium redox flow battery (VRFB) is a promising candidate for renewable energy storage applications due to its high energy efficiency, low toxicity, and long lifespan. The half-cells of the battery are separated by a membrane through which ions migrate in order to maintain charge balance. Nafion, a perfluorinated polymer with sulfuric acid functional groups that facilitate proton transport, is the most widely used cation-exchange membrane due to its high proton conductivity and chemical and thermal stability. However, the low ion selectivity of Nafion permits positively charged vanadium ions to also cross through the membrane into the opposite electrolyte resulting in self-discharge of the battery, reducing efficiency.
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