NH2-UiO-66 coated fibers to balance the excellent proton conduction efficiency and significant dimensional stability of proton exchange membrane

The proton exchange membrane (PEM) with high sulfonation degree (DS) exhibits high proton conductivity but poor dimensional stability and mechanical properties. In order to improve dimensional stability and strength of PEM as well as maintaining excellent proton conductivity, we proposed to modify pre-oxidized polyacrylonitrile nanofibers (PPNF) through amino functionalization with NH2-UiO-66 (NU6). Compared with primary sulfonated poly (ether ether ketone) (SPEEK), the dimensional stability of 1.3% NU6 @PPNF-SPEEK composite membrane increase 30% due to the chemical crosslinking structure of PPNF. The acid-enriched layers, which provide an efficient proton transport channel, form along the fibers because of interaction between NU6 and -SO3H, since then composite membranes exhibit higher proton conductivity. Most importantly, this study firstly revealed the mechanism of formation process of sulfuric acid-rich layer through FTIR and EDS, which could provide a strategy for constructing and adjusting the proton transport channel efficiently. In summary, NU6@PPNF-SPEEK with excellent proton conductivity, outstanding dimensional stability and great mechanical properties in hydrated condition has been successfully fabricated.