Preparation And Performance Of Sulfonated Poly(Ether Ether Ketone Ketone) Proton Exchange Membranes

Direct methanol fuel cell（DMFC）possesses the characteristics of high energy density,simple and convenient supply,rich fuel sources,easy storage of methanol and low environmental pollution.Hence,DMFC is considered a green and most valuable energy conversion technology.However,there are still great challenges in the application of DMFC.The main problem lies in its high cell production cost,which mostly comes from the precious metal catalyst and the proton exchange membrane（PEM）.PEM is the core component of DMFC,which plays the role of isolating methanol fuel penetration and providing proton transfer channels.The property of PEM directly affects the performance and service life of fuel cell.The high proton conductivity of PEM is often accompanied by high methanol permeability and low mechanical properties.Therefore,it is a challenge to simultaneously improve proton conductivity,methanol resistance and physicochemical stability of PEMs used in DMFC.Sulfonated poly（ether ether ketone ketone）（SPEEKK）,as a member of the sulfonated aromatic polymer family,has excellent mechanical properties and oxidation hydrolysis stability.When the degree of sulfonation is high,its proton conductivity is high,but the methanol resistance decreases and swelling gets serious,which affects the mechanical stability of SPEEKK.Therefore,it is urgent to modify SPEEKK to improve its proton conductivity and comprehensive performance.In this paper（1）SPEEKK was prepared by post sulfonation method.SP/PVP composite membranes were prepared by mixing different concentrations of polyvinyl pyrrolidone（PVP）and SPEEKK.Then the polyorganosilicon（PO）containing various functional groups prepared by emulsion polymerization was introduced into SP/PVP20 with the best selectivity to prepare the multi crosslinked SP/PVP-PO composite membranes.Compared to SP/PVP20,SP/PVP-PO membranes exhibited better performance,including lower methanol diffusion and higher proton conduction.The membrane containing 30 wt%PO showed the highest selectivity(2.31×10⁵Ss·cm^-3),which was approximately 11 times of commercially available Nafion^@117 membrane.（2）SPEEKK was prepared by copolymerization of sulfonated monomers.In order to improve the comprehensive performance of SPEEKK membrane,multiple crosslinked composite membranes（PSP/PO-SF）were prepared by introducing PO and sulfonic acid functionalized graphene oxide（SFGO）containing various functional groups into SPEEKK.The performance of PSP/PO-SF membranes were significantly improved,including mechanical properties,dimensional stability,proton conductivity,methanol resistance,selectivity,oxidation and hydrolysis stability,etc.The multiple crosslinked composite membrane with 3 wt%SFGO showed the highest conductivity(0.074 S·cm^-1 at 25℃),the lowest methanol diffusion coefficient(3.56×10^-7 cm²·s^-1),and the best selectivity(2.08×10⁵ Ss·cm^-3).In addition,the maximum power density(73.76 m W·cm^-2)of the membrane with 3 wt%SFGO was higher than that of commercial Nafion^@117(61.59 m W·cm^-2)under identical experimental conditions.