SPEEK–zirconium hydrogen phosphate composite membranes with low methanol permeability prepared by electro-migration and in situ precipitation

Sulfonated poly(ether ether ketone) (SPK)–zirconium hydrogen phosphate (ZrP) composite membranes were prepared by electro-driven migration of Zr4+ and simultaneous in situ precipitation of ZrP using phosphoric acid under different electrical gradient, in order to avoid loss in its mechanical stability. Degree of sulfonation was estimated from 1H NMR and ion-exchange capacity study that was found to be 61% and 57%, respectively. In this method Zr4+ and HPO42− were allowed to diffuse within the pores/channels of the preformed SPK membrane under given electrical gradient and ZrP was precipitated within the membrane matrix. ZrP loading density was measured as a function of applied electrical gradient for a definite reaction time (4 h) and electrolytic environment. Membranes with varied ZrP loading densities were characterized for their thermal and mechanical stabilities, physicochemical and electrochemical properties using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), water content, proton conductivity and methanol permeability. No loss in thermal and mechanical stability of membranes was observed due to incorporation of inorganic component (ZrP) in the membrane matrix. Although the composite membranes exhibited low proton conductivity in comparison to SPK membrane at room temperature, but the presence of the inorganic particles led to an improvement in high temperature conductivity. Selectivity parameter of these composite membranes was estimated at two temperatures namely 30 and 70 °C, in latter case it was found significantly higher than that for Nafion membrane (0.79×105 Sscm−3) under similar experimental conditions.

Graphical abstractSchematic diagram of a electrochemical method for preparing SPEEK–ZrP nanocomposite membrane.Figure optionsDownload full-size imageDownload as PowerPoint slide