Nanofiber network composite membranes for proton exchange membrane fuel cells.

摘要

A new class of proton exchange membranes has been developed for H 2/air fuel cells. The nanofiber network composite membranes were prepared from electrospun fiber mats using the following proton conducting materials: (1) sulfonated poly(arylene ether sulfone) (sPAES) (2.5 mmol/g IEC), (2) sPAES (2.1 mmol/g IEC) with sulfonated octaphenyl polyhedral oligomeric silsesquioxane (sPOSS) (4.8 mmol/g IEC), (3) perfluorosulfonic acid (PFSA) (0.91 mmol/g IEC for DuPont's NafionRTM or 1.21 mmol/g IEC and 1.36 mmol/g IEC from 3M Corporation), and (4) 3M Corp. PFSA (1.21 mmol/g IEC) with sPOSS (4.8 mmol/g IEC). Membrane preparation involved three steps: (a) electrospinning a mat of proton conducting polymer nanofibers, (b) increasing the volume fraction of fibers in the mat and creating welds at fiber intersection points, and (c) impregnating the processed fiber mat with Norland Optical Adhesive (NOA) 63 to restrain fiber swelling when the membrane is equilibrated with liquid water or water vapor and to provide the required mechanical properties for fuel cell applications.;The electrospinning methods to produce sPAES, sPAES/sPOSS, PFSA, and PFSA/sPOSS proton conducting nanofibers were developed. For the case of electrospinning PFSA or PFSA/sPOSS, a high molecular weight inert and water soluble dopant (either poly(ethylene oxide) (PEO) or poly(acrylic acid) (PAA)) was added to the electrospinning solution at a concentration of 1--50 wt% (PEO) and 5--50 wt% (PAA). The proton conductivity of a 2.5 mmol/g IEC sPAES nanofiber network composite membrane exceeded that of NafionRTM 212 when the sPAES nanofiber volume fraction was greater than 0.70. A sPAES/sPOSS (65/35 wt/wt) nanofiber network composite membrane with a fiber volume fraction of 0.70 exhibited a proton conductivity of 0.072 S/cm at 30°C and 80% RH which exceeded the U.S. DOE's 2008 technical target (0.07 S/cm at 30°C and 80% RH) for fuel cell membrane conductivity. A nanofiber network composite membrane composed of 825 EW PFSA (1.21 mmol/g IEC) + sPOSS + PAA nanofibers (60/35/5 wt/wt/wt), where the fiber volume fraction was 0.74 exhibited a proton conductivity of 0.107 S/cm at 120°C and 50% RH which exceeded the U.S. DOE's 2009 technical target for membrane proton conductivity (0.1 S/cm at 120°C and 50% RH).