Applications of Porous Glass Membranes in Redox-Flow-Batteries - Investigations on the Influence of Membrane Thickness, Pore Structure and Surface Modification

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In an abstract of the 3rd sub-report of the 5th assessment report of the IPCC from 13.04.2014 it is stated that the greenhouse gas emission is rapidly increasing, though continuous work on climate protection. Therefore, it is necessary to intensify the activities in the field of regenerative energy. Just as important as power generation is also its storage. Redox-Flow-Batteries (RFB) are particularly suited for this purpose, showing high efficiencies as well as relatively low costs compared with, for example, Lithium ion batteries. Their modular design facilitates the production of stacks with few individual to several hundreds of parallel and serial cells. Though, such cells still show deficiencies, like relatively low current densities, high material costs of the used membranes as well as an ion crossover through the membrane, which leads to the formation of mixed potentials and thus to contamination of the electrolytes used. While the electrolyte systems in RFBs have continuously been enhanced and optimized, the separators used still mainly consist of nonporous and expensive Nafion®. Although other materials and composites are examined regarding their applicability as separators/membranes, these are mainly polymer based.Mechanically and chemically stable porous glasses (PG) are almost not investigated, even though they show a variety of benefits. Porous glass membranes provide the possibility of the flexible modification of their macroscopic geometry, pore sizes and surface properties. Hence porous glass membranes should be fully adaptable to the conditions in RFBs. The use of PG membranes allows high current densities and conductivities and the prevention of ion crossover by adjusting adequate surface properties. Thus, PG membranes represent an ideal model system for systematic investigations on the influence of different parameters, like porosity, pore size, pore structure, membrane thickness, surface charge, surface energy, etc., on the performance of RFBs, which is discussed controversially in the scientific literature.Therefore, we think it is reasonable to combine these two modern technologies in a novel way. For this purpose, porous glass membrane with tailor-made properties will be produced and investigated in a Vanadium Redox-Flow-Battery. The obtained results will be compared to those estimated for Nafion® membranes under the same conditions.