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Pre-stretched Recast Nafion for Direct Methanol Fuel Cells

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2008, Master of Sciences, Case Western Reserve University, Materials Science and Engineering.

Direct methanol fuel cell operation with uniaxially pre-stretched recast Nafion® membranes (draw ratio of 4) was investigated and compared to that with commercial (un-stretched) Nafion. The effects of membrane thickness (60-250 μm) and methanol feed concentration (0.5-10.0 M) on fuel cell power output were quantified for a cell temperature of 60°C, ambient pressure air, and anode/cathode catalyst loadings of 4.0 mg/cm2. Pre-stretched recast Nafion in the 130-180 μm thickness range produced the highest power at 0.4 V (84 mW/cm2), as compared to 58 mW/cm2 for Nafion 117. MEAs with pre-stretched recast Nafion consistently out-performed Nafion 117 at all methanol feed concentrations, with 33-48% higher power densities at 0.4 V, due to a combination of low area-specific resistance (the use of a thinner pre-stretched membrane, where the conductivity was the same as that for commercial Nafion) and low methanol crossover (due to low methanol solubility in the membrane). Very high power was generated with a 180 μm thick pre-stretched recast Nafion membrane by increasing the cell temperature to 80°C, increasing the anode/cathode catalyst loading to 8.0 mg/cm2, and increasing the cathode air pressure to 25 psig. Under these conditions the power density at 0.4 V for a 1.0 M methanol feed solution was 240 mW/cm2 and the maximum power density was 252 mW/cm2.

Water uptake and mobility data were collected and analyzed for pre-stretched films with draw ratios ranging from 1 to 7 in order to better understand the transport characteristics and fuel cell performance of these materials. Macroscopic gravimetric water uptake and the water self diffusion coefficient (by NMR) in pre-stretched films were found to be identical to that in commercial Nafion 117 films, regardless of the extent of elongation. The ratio of freezable/nonfreezable water in pre-stretched recast Nafion, the water electro-osmotic drag coefficient, and the spin-lattice relaxation time constant of deuterated water, however, decreased with increasing film elongation, up to a draw ratio of 4. The combined water results indicated that there are a greater number of smaller ionic/hydrophilic domains in pre-stretched recast Nafion, as compared to commercial Nafion. This result was confirmed by transmission electron microscopy of pre-stretched membrane cross sections. Equilibrium methanol sorption experiments revealed that the low methanol permeability in pre-stretched recast Nafion was associated with a decrease in the methanol partition coefficient.

Dr. Peter Pintauro (Committee Chair)
Dr. Joe Payer (Committee Chair)
Dr. Gerhard Welsch (Committee Member)
69 p.

Recommended Citations

Citations

  • Wu, P.-H. (2008). Pre-stretched Recast Nafion for Direct Methanol Fuel Cells [Master's thesis, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1212685669

    APA Style (7th edition)

  • Wu, Pin-Han. Pre-stretched Recast Nafion for Direct Methanol Fuel Cells. 2008. Case Western Reserve University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1212685669.

    MLA Style (8th edition)

  • Wu, Pin-Han. "Pre-stretched Recast Nafion for Direct Methanol Fuel Cells." Master's thesis, Case Western Reserve University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1212685669

    Chicago Manual of Style (17th edition)