A facile method to construct proton exchange membranes based on metal organic frameworks decorating binary polymer nanofibers

Abstract

Nanofibers are believed to effectively conduct protons by regulating proton conduction pathways in proton exchange membranes. In this study, binary polymer nanofibers comprising chitosan (CS) and polyvinyl alcohol (PVA) were fabricated using the electrospinning technique. CS/PVA nanofibers (CPNFs) were decorated with metal organic frameworks (MOFs) through the in situ growth process on the surface. The MOFs@CPNFs membrane was immersed in the sulfonated poly (ether ether ketone) (SPEEK)/N,N-dimethylformamide (DMF) solution to construct the (MOFs@CPNFs)-SPEEK membrane. The intermolecular hydrogen bonding formed among the components ensures the formation of stable microstructures of the composite membranes. The accelerated proton conduction process results in improved and stable conductivities even at subzero temperatures. Specifically, the phosphoric acid (PA)-doped composite membrane of (MOFs@CPNFs)-SPEEK/PA showed proton conductivities of (1.72 ± 0.19) × 10⁻² S cm⁻¹ at −30 °C, (4.01 ± 0.24) × 10⁻² S cm⁻¹ at 30 °C and (1.40 ± 0.09) × 10⁻¹ S cm⁻¹ at 160 °C. The excellent proton conductivity stability of composite membranes is confirmed by the proton conductivities in the heating–cooling cycle process and long-term test. Most importantly, the single proton exchange membrane fuel cell based on the (MOFs@CPNFs)-SPEEK/PA membrane presents peak power density values of 414.2 mW cm⁻² at 100 °C and 606.4 mW cm⁻² at 130 °C.