Modification and evaluation of membranes for vanadium redox battery applications

Several commercial ion exchange membranes were evaluated for application in the vanadium redox battery. The polyether membrane, DF120 cationic exchange membrane, showed the highest permeability to vanadium ions and the worst chemical stability in V(V) solution, while the divinylbenzene membrane, JAM anionic exchange membrane, showed the lowest permeability to vanadium ions and the best chemical stability in V(V) solution. In order to impart some cationic exchange capacity to the JAM anionic exchange membrane, sodium 4-styrenesulfonate was used to modify the anionic membrane by in situ polymerization. Measurements by infrared spectroscopy (IR) and cationic ion exchange capacity (IEC) verified that the modification procedure imparts cationic exchange capability to the membrane. Incorporation of cationic exchange groups to the anionic exchange membrane further results in a reduction in permeability to vanadium ions. The current and energy efficiencies averaged over 8 charge/discharge cycles of the cell with the treated JAM membrane were higher than that with the untreated JAM membrane. The current and energy efficiencies of the cell with the treated JAM membrane did not change over several charge/discharge cycles, which indicates good chemical stability of the treated membrane in the vanadium redox cell. The average efficiencies of the cell with the treated JAM membrane are higher than that with Nafion 117 over 8 charge/discharge cycles.