Transcript 下載/瀏覽
Reporter: Wen-Cheng Lin Teacher:Wei-Tung Liao Outline • Introduction • Materials • Experimental • Results and discussion • Conclusions Introduction(1) • The widely used PEMs for both hydrogen and methanol fuel cells are perfluorosulfonic acid membranes, such as DuPont’s Nafion. • These membranes have exceptional oxidative and chemical stability as well as high proton conductivity, which are suitable for PEMFCs. • However, some specific shortcomings such as high cost, low conductivity at high temperature and low humidity as well as high methanol crossover that decreases fuel efficiency have limited their applicability . Introduction(2) • During the last two decades, extensive efforts have been made to develop alternative hydrocarbon-based polymer electrolyte membranes in order to overcome the drawbacks of the current widely used Nafion membranes. • Among numerous alternative polymers, sulfonated poly(ether ether ketone)s (SPEEKs) are good candidates on account of their thermal oxidative stability, high glass transition temperature and high proton conductivity, which depend on their degree of sulfonation [27]. Materials(1) • SPEEK • NaBH4 • DMSO • triphenylphosphine (TPP) Materials(2) • Tetraglycidyl bis(p-aminophenyl)methane (Araldite MY721 epoxy resin) Experimental(1) • Hydroxylation of SPEEK DMSO (45 ml) and NaBH4 (0.0363 g) were added to a 100 ml round bottomed flask equipped with a reflux condenser and a drying tube. The mixturewas heated while stirred at 120 ◦C. Sodium form SPEEK (SPEEKNa) film cut in small pieces (4.5 g) was added. The mixture was stirred for 12 h at 120 ◦C. After cooling to room temperature, the solution was filtered and methanol (3 ml) added while stirring. Experimental(2) Fig. 1. Synthesis of SP30. Experimental(3) • Membrane casting and epoxy curing A 10 wt.% solution of partially hydroxyl-functionalized SPEEK with various weight concentrations of MY721 epoxy resin and 2.5 wt.% of TPP catalyst (based on epoxy resin weight) was mixed in DMSO and stirred until a transparent homogeneous solution was obtained. The solution was cast on a glass plate which was then placed in an oven and heated at 100 ◦C for 4 h, 150 ◦C for 2, 4, 8, 12 and 24 h. After cooling to room temperature, the membrane was peeled from the glass plate. Experimental(4) • In the first series, epoxy concentration was fixed at 1 eq of epoxy groups per hydroxyl group. The crosslinking time was varied from 2, 4, 8, 12 to 24 h. • Secondly, a series of crosslinked membranes were prepared with a constant curing time of 24 h, but with varied epoxy equivalents of 0.5, 1, 1.5, 2, 3 and 4 per hydroxyl group. Experimental(5) Fig. 2. Preparation of crosslinked SPEEK membranes. Experimental(1) • Acidification of membranes The crosslinked membranes were converted to the required acid form by immersion in 2mol/l sulfuric acid solution at 30 ◦C for 24 h, and then washed with deionized water to remove excess acid. • CNaOH : the concentration of NaOH solution • VNaOH is the consumed volume of NaOH solution • WS is the weight of the membrane sample • P is the methanol permeability coefficient (cm2/s) • k is the slope of the straight-line plot of methanol concentration in solution B versus permeation time (mol/(l s)) • VB is the volume of solution B (ml) • CA is the concentration of methanol in A cell (mol/l) • A is the membrane area (cm2) • L is the thickness of membrane (cm) Results and discussion FTIR • SP30 • SPEEK Fig. 3. FT-IR spectra of SPEEK and SP30. FTIR Fig. 4. Preparation of crosslinked SPEEK membranes. Fig. 5. Swelling ratio of SPEEK and crosslinked membranes at different temperature. Proton conductivity Fig. 6. Proton conductivity of SPEEK and crosslinked membranes at different temperature. Methanol permeability coefficient Fig.7. Methanol permeability coefficient of pristine SPEEK and crosslinked membranes at 30 ◦C. Selectivity Fig. 8. Selectivity of pristinte SPEEK and crosslinked membranes. Conclusions(1) • After crosslinking, all the membranes exhibited lower water uptake and swelling ratio relative to pristine SPEEK. • The methanol permeability coefficient of crosslinked membranesdecreased dramatically. • Although the proton conductivity modestly decreased to some extent, the overall performance of the crosslinked membranes was still superior. Conclusions(2) • The membranes crosslinked with 1–2 epoxy equivalents showed better selectivity than pristine SPEEK and Nafion117 taking into consideration the methanol swelling ratio and proton conductivity comprehensively. The End