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.

Polymer membranes are central to the proper operation of several processes used in a wide range of applications. The production of these membranes relies on processes such as phase inversion, stretching, track etching, sintering, or electrospinning. A novel and competitive strategy in membrane production is the use of additive manufacturing that enables the easier manufacture of tailored membranes. To achieve the future development of better membranes, it is necessary to compare this novel production process to that of more conventional techniques, and clarify the advantages and disadvantages. This review article compares a conventional method of manufacturing polymer membranes to additive manufacturing. A review of 3D printed membranes is also done to give researchers a reference guide. Membranes from these two approaches were compared in terms of cost, materials, structures, properties, performance. and environmental impact. Results show that very few membrane materials are used as 3D-printed membranes. Such membranes showed acceptable performance, better structures, and less environmental impact compared with those of conventional membranes.

Vanadium redox flow batteries (VRFB) are among the most promising approaches to efficiently store renewable energies. In such battery type, Nafion is commonly used as membrane material but suffers from high vanadium crossover and cost. These drawbacks negatively influence the widespread commercial application of VRFBs. Alternative membrane materials with high performance and low cost are thus being developed to address these shortfalls. Among those, possible materials for the VRFB membrane is sulfonated polyether ether ketone (SPEEK), which recently attracted considerable attention due to its low cost, combined with mechanical and chemical stability, and ease of preparation. This review summarizes the research activities related to the development of SPEEK-based membranes for VRFB applications and gives an overview of the properties of PEEK and its sulfonated form. A critical analysis on the challenges of SPEEK-based membranes is also discussed.