Sulfonated graphene oxide/sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) as a potential proton exchange membrane for iron air flow battery application

A series of proton exchange membranes (PEMs) of sulfonated poly(2,6-dimethyl1,4-phenylene oxide) (SPPO) with different sulfonated graphene oxide (SGO) (0, 0.25, 0.5, 0.75, 1.0, 1.5%) were prepared for possible application in Iron-air/flow battery. The presence of SGO in the membrane improved the water uptake of all membranes prepared and decreased the swelling ratio. The SPPO/1% w/w SGO showed good properties with higher water uptake of 44.1%, water retention of 42.48% and swelling ratio of 21.4% at 25 degrees C. However, the 0.75% SGO exhibited the highest proton conductivity of 0.98 S/cm and better dispersion, elemental distribution, and morphology. In addition, SGO improved the thermal stability of all composite membranes. The chemical stability of all membranes remained good after 7 days in a 1 M HCL solution. The SPPO/0.75%w/w SGO showed increased proton conductivity when degradation properties were evaluated. Compared to Nafion 117, all composites showed lower iron crossover. Nafion had a high permeability of 3.03 x 10(-7) cm(-2)/s, which is 75% higher than the 7.6 x 10(-8) cm(-2)/s of SPPO/ SGO-1.5% and 52% higher than the 1.46 x 10(-7) cm(-2)/s of SPPO/SGO-0.75%. The results indicate that SGO is a good inorganic filler for the composite proton exchange membrane and stable enough for possible application in an iron-air/flow battery.