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Enhancement of service life of polymer electrolyte fuel cells through application of nanodispersed ionomer

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Science Advances  31 Jan 2020:
Vol. 6, no. 5, eaaw0870
DOI: 10.1126/sciadv.aaw0870
  • Fig. 1 Schematics of Nafion ionomers on the catalyst surfaces.

    (A) Distribution of conventional ionomers synthesized by emulsion polymerization. (B) Distribution of the laboratory-made ionomers synthesized by SCF process. Enlarged conceptual diagram showing the distribution of both conventional and prepared ionomer on the Pt/C catalyst surface. The SCF process contributes to the formation of nanodispersed Nafion ionomer, leading to improved electrochemical performance and durability.

  • Fig. 2 Physical properties of solidified-state ionomers.

    (A) Particle size distribution pattern by DLS. Most D521 particles are in the ~100-nm range, but the laboratory-made dispersion has a large amount of particles in the nanoscale region. (B) Viscosity behaviors of D521 and ND. Because of the relatively small ionomer particle sizes, ND shows four times the viscosity of D521. (C and D) XRD patterns of solid-state D521 and ND. The sharp XRD peak of ND ionomer indicates that semicrystalline ND ionomer chains are relatively uniformly packed with improved regularity. This feature is quantitatively analyzed by deconvoluting each XRD peak as individual amorphous (green line) and crystalline (blue line) peaks with Gaussian equations. (E) SAXS spectra of solid-state D521 and ND. The narrow width of the SAXS peak of ND indicates the relatively small average size of its hydrophilic domains. TEM images of (F) D521 and (G) ND to compare the size difference of hydrophilic domains (dark regions). (H) Proton conductivities of D521 and ND membrane coupons obtained in deionized water as a function of temperatures. Each coupon was thermally treated at 140°C for 1 hour. a.u., arbitrary units.

  • Fig. 3 Surface morphologies and pore distributions of MEAs with conventional D521 ionomer and ND ionomer.

    SEM results of (A to C and G) MEA with conventional D521 ionomer and (D to F and H) MEA with ND ionomer. (I) MIP results of MEA with conventional D521 ionomer (blue) and ND ionomer (red). The inset is an enlarged graph showing the pore distribution near 0.1 to 10 μm.

  • Fig. 4 Polarization curves and EIS results of MEAs with conventional D521 ionomer and ND ionomer before and after AST.

    Fuel cell performances of MEAs before and after AST. (A) MEA with conventional D521 ionomer. (B) MEA with ND ionomer in air. EIS results for MEAs before and after AST. (C) MEA with conventional D521 ionomer. (D) MEA with ND ionomer in air.

  • Table 1 Basic characteristics of D521 and ND in dispersed and membrane states.

    UnitD521ND
    Mn*(kDa)6695
    Mw*(kDa)193.7293.5
    PDI*(−)2.932.15
    Density(g cm−3)1.932.32
    Water uptake(%)35.226.7
    Crystallinity(%)25.841.8

    *GPC measurement using an N-methyl-2-pyrrolidinone (NMP) column. Each ionomer sample was dissolved in NMP containing 0.05 M LiCl.

    †Before the measurements, each ionomer dispersion was converted to membrane coupons after thermally drying at 60°C for 8 hours and 140°C for 1 hour.

    • Table 2 Mechanical strengths of D521 and ND ionomers after thermal treatment.

      Thermal
      treatment
      temperature*
      Tensile
      strength
      Elongation
      (°C)(MPa)(%)
      ND608.760.9
      12013.568.5
      14023.1180.8
      D521140
      22019.5199.1

      *All thermal treatments were performed in a vacuum oven under N2 atmosphere for 1 hour.

      †Not applicable.

      Supplementary Materials

      • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/5/eaaw0870/DC1

        Fig. S1. Polarization curves for MEAs containing D521 and ND ionomers with different contents.

        Fig. S2. Polarization curves and EIS results of MEAs before and after AST in O2.

        Fig. S3. Polarization curves and tabulated results of MEAs with different ionomer loadings before and after AST in air.

        Fig. S4. Cyclic voltammograms of MEAs before and after AST.

        Fig. S5. TEM images and particle distribution of Pt/C catalysts before and after AST.

        Table S1. Current densities at 0.6 V and maximum power densities of MEA-0, MEA-10, MEA-20, and MEA-30 in O2 and air.

        Table S2. Influence of AST on current densities at 0.6 V and maximum power densities of MEA-0 and MEA-20.

        Table S3. EIS results for MEA-0 and MEA-20 after AST.

      • Supplementary Materials

        This PDF file includes:

        • Fig. S1. Polarization curves for MEAs containing D521 and ND ionomers with different contents.
        • Fig. S2. Polarization curves and EIS results of MEAs before and after AST in O2.
        • Fig. S3. Polarization curves and tabulated results of MEAs with different ionomer loadings before and after AST in air.
        • Fig. S4. Cyclic voltammograms of MEAs before and after AST.
        • Fig. S5. TEM images and particle distribution of Pt/C catalysts before and after AST.
        • Table S1. Current densities at 0.6 V and maximum power densities of MEA-0, MEA-10, MEA-20, and MEA-30 in O2 and air.
        • Table S2. Influence of AST on current densities at 0.6 V and maximum power densities of MEA-0 and MEA-20.
        • Table S3. EIS results for MEA-0 and MEA-20 after AST.

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