Sulfonated polyethersulfone based composite membranes containing heteropolyacids laminated with polypyrrole for electrochemical energy conversion devices

Composite membranes based on sulfonated polyethersulfone (SPES) with different heteropolyacids (HPAs) such as silicotungstic acid (STA) and tungstophosphoric acid (TPA) laminated with polypyrrole (Ppy) were developed and investigated for its suitability as a polymer electrolyte membrane (PEM). In order to prevent the leaching out of HPAs from the composite membranes, Ppy was laminated over the composite membrane matrices through in situ polymerization technique. The performance of the composite membranes was evaluated with respect to ion exchange capacity, water uptake, proton conductivity, stability and methanol permeability, etc. The atomic force microscopic images showed that heteropolyacids had better compatibility with SPES membrane matrix. The SPES/HPAs membranes achieved an acceptable proton conductivity with increasing in weight ratios of HPAs and reach the highest proton conductivity of 1.41 × 10− 2 S cm− 1 for SPES/STA(30%) and 6.9 × 10− 3 S cm− 1 for SPES/TPA(30%) respectively. Surface modification of SPES/HPAs composite membranes by laminating with Ppy led to a decrease in IEC values compared with that of SPES/HPAs composite matrix. The methanol permeability was reduced after incorporating Ppy layers of the SPES/HPAs composite membranes, whereas stability of the composite membranes was increased. The methanol permeability of all the composite membranes declined more significantly. The relative selectivities of the all composite membranes, improved remarkably, which translates to better overall performance. The SPES/STA(30%)/Ppy membrane exhibits highest selectivity parameter of 8.4 × 104 S cm− 3 s than all the other membranes.