USE OF PROTON EXCHANGE MEMBRANE IN IRON-CHROMIUM LIQUID FLUID BATTERY

The present invention regarding the use of proton exchange membranes for Fe/Cr redox cells belongs to the area of flow redox batteries (or flow redox cells). A proton exchange membrane works as a separator between the positive and negative electrodes in Fe/Cr redox flow cell. These proton exchange membranes are perm-selective to hydrogen ions, that is, protons, with Fe3+ permeability ¤ 1200 and 2500 µg Fe 3+ /hr¢cm2¢M under room temperature and 65 oC respectively. They have the conductivity (to electrolyte) ¥ 0.03 S¢cm-1 at room temperature and atmospheric pressure, or the resistivity ¤0.65 ©¢cm2 and 0.32 ©¢cm2under room temperature and 65 oC respectively (for the membrane thickness of 120 µm). The proton exchange membranes are made of sulfonated polyether ether ketone (sPEEK) polymers,sulfonated poly (phthalazinone ether sulfone ketone) (sPPESK) polymers, or others. This modern type of proton exchange membranes, which are usually developed for fuel cells, work as separators between positive and negative electrodes in Fe/Cr redox flow batteries. Unlike Nafion membranes, this type of proton exchange membranes is a kind of polymer membranes based on carbohydrates and has a much lower cost. With comparison to the proton exchange membranes in early years, these membranes have better proton selectivity and conductivity. And, it lowers the production cost of the Fe/Cr redox cell while holding high efficiency of the cell design simultaneously.