Highly Selective Anion Exchange Membranes for Non-aqueous Redox Flow Batteries

There is a need for long duration energy storage at wind farms and solar photovoltaic facilities and redox flow cell batteries could potentially solve this problem. Non-aqueous redox flow batteries are superior to the more common aqueous flow batteries because they can avoid the problems caused by the breakdown of water at high voltage. However, most non-aqueous flow batteries are based on transition metal complexes and an organic soluble supporting salt with an anion that is usually BF -., and they require a selective anion transport membrane to allow the BF4- to cross back and forth, while preventing diffusion of the slightly larger metal complexes, such as vanadium acetylacetonate or ruthenium bipyridine. Very few membranes have nanopores in this required size range needed to provide this selectivity. Lastly, the membranes also must be mechanically stable and resist swelling by the organic solvent. There is a need for new anion-exchange membranes for non-aqueous redox flow batteries that has all of the required traits: high anion-selectivity, durability and the ability to resist swelling in organic solvents, all while maintaining highly uniform pores, and controlled tortuosity. This project will develop a nanoporous polymer anion-exchange membrane that features highly uniform, well-aligned, nanostructured channels formed by the self-assembly of polymerizable surfactants. The membrane will contain approximately 7 to 8-Angstrom diameter pores, entirely composed of positively charged cations that will act as anion diffusion channels. The pores will contain non-aqueous electrolyte solvent, and the channels will define extremely conductive, low- tortuosity pathways creating a separator material with high conductivity, excellent selectivity and that is resistant to swelling by organic solvents. In Phase I, TDA will prepare nanoporous anion-exchange membranes and measure their performance in non-aqueous redox flow batteries. We will vary the geometry of the polymerizable surfactants and evaluate the structure-property relationship of the starting surfactant molecular geometry and the resulting nanoporous structure. The membrane processing methods will also be varied and process- structure-property relationships will then be used to guide our development of our new, highly selective anion-exchange membrane materials. Commercial applications include redox flow batteries for long duration energy storage (e.g. wind farms, solar photovoltaic facilities and back-up power systems).