A comparative study on physiochemical, thermomechanical, and electrochemical properties of sulfonated poly(ether ether ketone) block copolymer membranes with and without Fe₃O₄ nanoparticles

The composite structure, good porosity, and electrochemical behavior of proton exchange membranes (PEMs) are important characteristics, which can improve the performance of polymer electrolyte fuel cells (PEFCs). In this study, we designed and synthesized an XY block copolymer via a polycondensation reaction that contains sulfonated poly(ether ether ketone) (SPEEK) (X) as a hydrophilic unit and a fluorinated oligomer (Y) as a hydrophobic unit. The prepared XY block copolymer is composed of Fe₃O₄ nanoparticles to create composite architecture, which was subsequently treated with a 1 M H₂SO₄ solution at 70 °C for 1 h to eliminate Fe₃O₄ and generate a pores structure in the membrane. The morphological, physiochemical, thermomechanical, and electrochemical properties of bare XY, XY/Fe₃O₄-9 and XY(porous)-9 membranes were measured and compared in detail. Compared with XY/Fe₃O₄-9 composite, the proton conductivity of XY(porous)-9 membrane was remarkably enhanced as a result of the existence of pores as nano-conducting channels. Similarly, the XY(porous)-9 membrane exhibited enhanced water retention and ion exchange capacity among the prepared membranes. However, the PEFC power density of XY(porous)-9 membrane was still lower than that of XY/Fe₃O₄-9 membrane at 60 °C and 60% relative humidity. Also, the durability of XY(porous)-9membrane is found to be lower comparedwith pristine XY and XY/Fe₃O₄-9 membranes as a result of the hydrogen crossover through the pores of the membrane.