Research ArticleELECTROCHEMISTRY

Conformation-modulated three-dimensional electrocatalysts for high-performance fuel cell electrodes

See allHide authors and affiliations

Science Advances  21 Jul 2021:
Vol. 7, no. 30, eabe9083
DOI: 10.1126/sciadv.abe9083
  • Fig. 1 Geometric control of 3D PtNAs via nTP.

    (A) A schematic illustration of the fabrication process for the 3D Pt electrocatalysts using the nTP process. Scanning electron micrography images of (B) a monolayer, (C) double layers, and (D) multilayers of PtNAs (left: pitch, 50 nm/width, 20 nm; center: pitch, 200 nm/width, 50 nm; and right: pitch, 1.2 μm/width, 200 nm). (E) Complex PtNAs stacked with a 45°, 30°, and freestanding nanostructure.

  • Fig. 2 Characterization of fabricated PtNAs by TEM.

    (A) A schematic illustration shows dense PtNWs (pitch, 200 nm/width, 50 nm). (B) High-resolution TEM image of the Pt nanowire and corresponding (C) FFT of the whole HRTEM image (yellow box). (D and E) In situ TEM-ASTAR crystal orientation mapping of dense PtNWs along z directions during thermal treatment at 600°C. The inset indicates a color-coded inverse pole figure. The mapping time required to obtain an image is about 40 min, and it was observed in the same sample although not in the same position because of the change in position during the thermal treatment and mapping process. The lower part shows the corresponding crystalline orientation distribution diagram.

  • Fig. 3 Characterization of fabricated PtNAs by XPS and XAFS.

    (A) XPS of Pt (4f) and (B) the ratio of Pt and Pt oxidation products in Pt/C and dense PtNA. (C) Pt L3-edge x-ray adsorption near-edge structure spectra of Pt/C and dense PtNA. (D) The coordination number for Pt-Pt and (E) Fourier transform magnitude spectra are shown for the Pt L3 edge of Pt/C and dense PtNA.

  • Fig. 4 Liquid half-cell test.

    (A) The transfer process for fabricated PtNA on glassy carbon or membrane substrates to prepare samples for electrochemical evaluation. (B) The ORR and (C) CV curves of Pt/C and dense PtNA are compared. The inset indicates the corresponding Tafel plot. (D) Mass and specific activities of Pt/C and dense PtNA. The ORR curves during the accelerated degradation test (ADT) (0.6 to 1.1 V, 6000 cycles) for (E) Pt/C and (F) dense PtNA. (G) ECSA retention rate of Pt/C and dense PtNA during the ADT. The ORR curves were acquired in a solution of O2-saturated 0.1 M HClO4, and the CV and ADT tests were conducted in a solution of Ar-saturated 0.1 M HClO4.

  • Fig. 5 Multiscale PtNA and single-cell test.

    (A) A schematic illustration showing a multiscale PtNA. Polarization curves of Pt/C and various PtNA-based MEAs are shown under an atmosphere of H2/air (B) without outlet pressure and (C) with a total outlet pressure of 150 kPa. (D) Oxygen gains were calculated using the potential difference observed upon exposure to oxygen or air, respectively. (E) The differences in power density between Pt/C and various PtNAs MEAs are shown for a H2/air atmosphere with a total outlet pressure of 150 kPa. CV curves of (F) Pt/C and (G) multiscale PtNA are shown before and after ADT (1.0 to 1.5 V, 5000 cycles).

  • Fig. 6 Numerical simulations based on computational fluid dynamics.

    (A) Comparison of simulated (lines) and measured (symbols) polarization curves under an operating pressure of 1 atm, (B) individual voltage losses due to ORR kinetic polarization and ohmic polarization across the cathode catalyst layer, (C) the average oxygen concentrations in the cathode catalyst layer as a function of operating current density, and (D) comparison of through-plane liquid saturation profiles for three different cathode catalyst layer designs at 1.0 A cm−2.

  • Table 1 Kinetic, physiochemical, and transport properties.
    DescriptionValueRef.
    Exchange current density (i0ref)Anode CL2350 A m−2(47)
    Cathode CL6.0 × 10−4 A m−2(47)
    Reference H2/O2 molar concentration (Cref)40.88 mol m−3(48)
    Transfer coefficients (α)Anode CLαa = αc = 1(48)
    Cathode CLαc = 1
    Activation energy (Ea)Anode CL10 kJ mol−1(47)
    Cathode CL70 kJ mol−1(49)
    Reaction order in the electrode (r)Anode CL1/2(48)
    Cathode CL3/4
    Porosity of the GDL (𝜀GDL)0.6Assumed
    Porosity of the anode CL (𝜀CL)0.5Assumed
    Porosity and permeability of the dense PtNA (Kna)50%, 1.0 × 10−12 m2Estimated
    Porosity and permeability of the sparse PtNA (Ksp)86.9%, 3.0 × 10−11 m2Estimated
    Permeability of the anode CL (KaCL)1.0 × 10−13 m2Assumed
    Permeability of the GDL (KGDL)5.0 × 10−13 m2Assumed
    ECSA per catalyst layer volume of dense PtNA catalyst layer (ana)6.0 × 107/mEstimated
    ECSA per catalyst layer volume of sparse PtNA catalyst layer (asp)5.038 × 106/mEstimated
    ECSA per catalyst layer volume of multiscale PtNA catalyst layer (amul)1.114 × 107/mEstimated
    Dry membrane density (ρdry, mem)2000 kg m−3(50)
    Equivalent weight of electrolyte in membrane (EW)1.1 kg mol−1(50)
    Faraday constant (F)96,487 C mol−1
    Universal gas constant (R)8.314 J mol−1 K−1
    Catalyst coverage coefficient (nc)1.5
    Effective electronic conductivity in the narrow and sparse PtNA (σPtNA)1.2 × 105 S m−1Estimated
    Effective electronic conductivity in the Pt/C (σCL)1000 S m−1(48)
    Effective electronic conductivity in the GDL (σGDL)10,000 S m−1(48)
    Effective electronic conductivity in the graphite BP (σGraphite)20,000 S m−1(48)
    Surface tension (σ)0.0625 N m−1(48)
    Contact angle of GDL, CL (θ)92°, 92°
    Liquid water density (ρl at 65°C)980 kg m−3
    Liquid water viscosity (μl)3.5 × 10−4 N s m−2(48)
    Thermal conductivity of the hydrogen (kH2)0.2 W m−1 K−1(50)
    Thermal conductivity of the oxygen (kO2)0.0296 W m−1 K−1(50)
    Thermal conductivity of the water vapor (kH2O)0.0237 W m−1 K−1(50)
    Thermal conductivity of the nitrogen (kN2)0.0293 W m−1 K−1(50)
    Thermal conductivity of membrane (kmem)0.95 W m−1 K−1(48)
    Thermal conductivity of GDL/CL5.0/1.0 W m−1 K−1(48)
    Thermal conductivity of graphite20 W m−1 K−1(48)

Supplementary Materials

  • Supplementary Materials

    Conformation-modulated three-dimensional electrocatalysts for high-performance fuel cell electrodes

    Jong Min Kim, Ahrae Jo, Kyung Ah Lee, Hyeuk Jin Han, Ye Ji Kim, Ho Young Kim, Gyu Rac Lee, Minjoon Kim, Yemin Park, Yun Sik Kang, Juhae Jung, Keun Hwa Chae, Eoyoon Lee, Hyung Chul Ham, Hyunchul Ju, Yeon Sik Jung, Jin Young Kim

    Download Supplement

    This PDF file includes:

    • Supplementary Text
    • Figs. S1 to S25
    • Tables S1 and S2
    • References

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article