(60a) Development of a Flat-Sheet Composite Membrane for Alkaline Water Electrolysis: A Statistical Study Using Response Surface Methodology

Phase inversion technique by means of immersion precipitation is widely used for fabricating asymmetric polymeric membranes. Asymmetric membranes consist of a thin and dense top layer called the skin layer and a porous substructure. Such membranes are used on electrolysis to separate the anode and cathode compartments and prevent the mixing of gases which evolve at the two electrodes. While prevention of gas crossover is a major function of the membrane separator, it should accomplish this without contributing a significant voltage drop. In this study, polysulfone-zirconium dioxide flat sheet membranes have been fabricated by using the phase inversion method for application in alkaline water electrolysis. Synthesis parameters such as zirconia loading, solvent extraction (pre-evaporation and coagulation) temperature and time affect the membrane morphology and hence its performance. The dense layer is significantly affected by the rate of solvent evaporation. A volatile co-solvent is used to reduce the formation of large finger-like pores ending in pin-holes on the membrane surface, increasing the pre-evaporation time can increase the dense layer thickness. Addition of tetrahydrofuran (THF) as a co-solvent to N-Methyl-pyrrolidone (NMP) solvent shows a significant morphological change as expected. The membranes were evaluated by measurements of bubble point pressure and resistivity. Membranes prepared with THF exhibited higher bubble point pressure. A response surface methodology has been used to optimize the concentration of THF, oven drying time and polysulfone concentration. Two factor interaction and Quadratic mathematical models for resistivity and bubble point pressure have been proposed and verified using diagnostic plots, which describe the responses within the ranges of factor investigation.