Preparation And Properties Of Acid-base Molecule-enhanced Blends For Proton Exchange Membranes

Proton exchange membrane fuel cells (PEMFCs) have been widely investigated asone of the promising clean future power sources because of their absence of pollutantemission and high energy conversion efficiency. As the solid electrolyte fortransferring protons as well as separating the fuel and the oxidant between electrodes,proton exchange membranes (PEMs) are the key elements for a high-efficiencyPEMFC system. Compared with the limited factor of perfluorosulphonic acid (PFSA)polymers Nafion (DuPont) which has high cost, low operation temperature (≤80°C),high methanol crossover, and environmental recycling uncertainties, newhigh-performance proton conductive membranes as an alternative material are causedmore and more attention.Blending is a facile process to improve the comprehensive properties of a matrix.As we know, SPEEKs with high ion-exchange capacities (IEC) often have relativelyhigh swelling ratio and low mechanical properties under humid circumstance and atan elevated temperature. Introducing such polymeric components as PBI, PVDF, PEIand PAI into SPEEK membranes is another method to improve thermal stability anddecrease the methanol permeability without sacrificing mechanical integrity of themembranes. Among them, polybenzimidazole (PBI) is a kind of high-performancepolymer that exhibits excellent mechanical and thermal properties. Recently,polybenzimidazole-based PEMs have been investigated. Some researches focusprimarily on the study of the acid-base blend membranes based on PBIs. Themotivation of these efforts is to improve the properties such as mechanical stabilityand strong resistance to fuel crossover.It is well known that the improvement on the solubility of the PBIs is one ofimportant topics. In our work, a novel soluble PBI containing flexible ether linkages and pendant phenyl groups (Ph-PBI) was synthesized, and firstly incorporated into asulfonated poly(ether ether ketone)(Ph-SPEEK) in order to form a new family ofmolecule-enhanced acid-base blend membranes. The properties related to fuel cellapplications, such as proton conductivity, water uptake and methanol permeability,were thoroughly evaluated. A series of compatible acid–base blend membranes weredeveloped by incorporating a soluble phenylated polybenzimidazole (Ph-PBI) into ahighly sulfonated poly(ether ether ketone). Novel SPEEK/PBI membranes arehomogeneous and highly transparent. The excellent miscibility is attributed to thesimilarity of the structure and the acid-base interactions between SPEEK and PBI. Allblend membranes exhibited much lower water uptake and swelling ratio than purePh-SPEEK. Also the mechanical property, methanol permeability, oxidative, thermalstability and selectivity are significantly improved by adding PBI into SPEEK system.At an elevated temperature, several membranes exhibited acceptable protonconductivities. Combined with all these advantages, the Ph-SPEEK/Ph-PBI may be anew family of potential PEM materials for fuel cell applications.