Surface modification and application of porous membranes for all-vanadium redox flow batteries

The porous membranes are well known with their cost advantage which is also meant an alternative for further commercialization of redox flow batteries in the future in the literature. However, they suffer from the cross-over of redox active species despite their cost advantages. Correspondingly to these factors, the aim of this thesis is to develop the permeability decrease of Amer-Sil FF60 porous membrane via surface modification. FAP® 450 (FuMA-Tech, Germany) (as anionic ion exchange membrane), Nafion® 117 (DuPont, the USA) (as cationic ion exchange membrane) and Amer-Sil FF60 porous membrane (Amer-Sil, Luxembourg) were employed in this study. Amer-Sil FF60 porous membrane's one face was modified with two different proportions of Nafion® (5, 7%, wt) dispersion such as (0,5:1) and (1:1). Spraying technique was utilized as modification method. According to the characterization values, the diffusion of V4+ ions could be declined with upon the addition of Nafion (5, 7%, wt). It was observed that the improvement of Amer-Sil FF60 membrane's selectivity could be achieved with the addition of Nafion (5, 7%, wt) dispersion and correspondingly to this, it was reported that it could remarkably be provided a capacity increase through the modified membranes. However, it couldn't be maintained the ionic conductivity as same as possible. With the addition of Nafion® (5,7 %, wt) dispersion, both proton conductivity and hydrophilicity degrees were decreased owing to the hydrophobic group of polytetrafluoroethylene (PTFE) which is the characteristic group of Nafion® (5,7 %, wt) dispersion. The chemical stability test was only applied to the Amer-Sil FF60 membrane and observed that it was stable in the highly acidic environment. Moreover, it was observed that the coloumbic, energy efficiency and power performances of modified porous membranes were approximately increased 10-15 % more than unmodified Amer-Sil FF60 porous membrane. According to the cell tests, it was denoted that the modified Amer-Sil FF60 membrane's performances could be accomplished circa 15% compared to the unmodified Amer-Sil FF60 porous membrane. As a result, it might be claimed that the modification of Amer-Sil FF60 may be considerable. According to the result of Nafion® (5,7%, wt) stability test, it was reported that the Nafion® (5,7%, wt) dispersion couldn not be stayed on the surface of the membrane as it was interacted via highly acidic vanadium electrolyte medium.