Review—Recent Membranes for Vanadium Redox Flow Batteries

Among energy storage technologies available or currently being developed, one of the most promising and attractive electrochemical system is the vanadium redox flow battery (VRFB). One of the key components in VRFB is the membrane required to separate the positive and negative half-cells. The role of this membrane is to prevent cross-mixing of vanadium ions while allowing the transport of certain ions to maintain the electrolytes' electro-neutrality. Such a membrane represents a sizeable fraction of the system's total cost while significantly affecting performance. Current research mostly consists of developing high-performance membranes offering high ionic conductivity, low permeability to vanadium ions, and good chemical and mechanical stability. A lower membrane cost is also desirable in order to reduce the overall system costs. This paper provides a comprehensive review of VRFB membranes and recent developments to allow for a better understanding of VRFB membranes' characterization techniques and their different manufacturing methods, while exploring materials suitable as VRFB membrane. Modeling of ion transport mechanisms through the separator and development prospects for a high-performance VRFB membrane are also discussed. The characteristics of the newly developed membranes are summarized to serve as a reference guide for researchers.