Research ArticleAPPLIED SCIENCES AND ENGINEERING

Toward digitally controlled catalyst architectures: Hierarchical nanoporous gold via 3D printing

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Science Advances  31 Aug 2018:
Vol. 4, no. 8, eaas9459
DOI: 10.1126/sciadv.aas9459
  • Fig. 1 3DP-hnp-Au exhibits control over structure that spans over seven orders of magnitude in length scales, from centimeters to nanometers.

    (A to C) Schematic illustrations of (A) 3D printing inks composed of mixtures of Au and Ag microparticles, polymer binder, and solvent (binder and solvent are represented as a green color). (B) The annealing step alloys the Au and Ag phases and removes the polymer binder to yield microscale porosity. (C) The dealloying step selectively removes the Ag phase, yielding the nanoscale porosity. Optical images of the 1-mm scale for multilayer woodpile-like architectures for printing (D), annealing and alloying (E), and dealloying steps (F). Scanning electron microscopy (SEM) images are shown depicting the structural evolution after the printing, annealing (and alloying), and dealloying steps for the 100-μm scale (G to I), 10-μm scale (J to L), 1-μm scale (M to O), and 100-nm scale (P to R). (S and T) Coarsening of the nanostructure after reannealing. Scale bars, 1 mm (D to F), 100 μm (G to I), 10 μm (J to L), 1 μm (M to O and S), and 100 nm (P to R and T).

  • Fig. 2 Fracture surfaces show that the structure is uniform throughout the dealloyed filaments.

    (A) SEM image showing fracture surface of a dealloyed filament. The large grains and faceted surfaces were formed during annealing. (B) Higher-resolution SEM image of the fracture surface and (C) highest-resolution SEM image of the fracture surface showing that nanoscale ligament and pore morphology extend throughout the volume of the printed filaments. Scale bars, 10 μm (A), 1 μm (B), and 100 nm (C).

  • Fig. 3 3D-printed Ag-Au structures with different macroscale geometries and microscale architectures.

    (A) Optical image of a single-layer array of parallel linear filaments. Optical images of multilayer high–aspect ratio (B) spiral, (C) honeycomb, (D) hollow pillar array, (E) linear simple cubic lattice, and (F) circular radial lattice structures. (A), (B), (C), and (E) shown as-printed, and (D) and (F) shown after annealing. Scale bars, 200 μm (A) and 2 mm (B to F).

  • Fig. 4 Electrochemical measurements for evaluation of the electrochemically accessible surface area and electric field–driven ion transport in np-Au and 3DP-hnp-Au.

    (A) Cyclic voltammograms (scan rate of 10 mV/s in 0.5 M H2SO4) collected from np-Au (60 mg) and 3DP-hnp-Au (59 mg) samples showing the Au reduction peaks used to calculate the surface area. (B) Capacitance versus frequency behavior from EIS data. (C) Charging kinetics of np-Au and 3DP-hnp-Au in response to potential jumps from Ei = 0 V to EF = 0.6 V (versus Ag/AgCl). The time (t1/2) where the current decreases to its half-maximum value, I/I0 = 0.5, is used to evaluate the charging kinetics. Dashed line indicates I/I0 = 0.5.

  • Fig. 5 Transport and catalytic reactions in np-Au and 3DP-hnp-Au.

    (A) Schematic illustration of the liquid flow cell. (B) Calculated and experimental plots of pressure drop versus flow speed show that the hierarchical structure of 3DP-hnp-Au reduces the pressure drop by >105 times compared to np-Au. (C) Schematic illustration of the gas flow through the catalytic fixed bed reactor. GC-MS, gas chromatography–mass spectrometry. (D) Plot of reaction rate versus time that compares the gravimetric reaction rate of 3DP-hnp-Au (80 mg) and np-Au (160 mg) catalysts for methanol oxidation to form methyl formate and carbon dioxide at elevated temperature.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/8/eaas9459/DC1

    Fig. S1. Rheology of the Ag and Au starting materials and composite inks.

    Fig. S2. Ligament size distribution.

    Fig. S3. Nyquist plot of np-Au and 3DP-hnp-Au at open-circuit potential.

    Fig. S4. Computational fluid dynamics (CFD) simulation of the velocity field of a square duct with a square orifice.

    Fig. S5. Pressure drop calculations in the square duct.

    Fig. S6. Methanol oxidation to methyl formate and carbon dioxide at 150°C.

    Fig. S7. Compressive stress-strain curve of 3DP-hnp-Au.

    Table S1. Methanol oxidation under different reaction conditions for np-Au and 3DP-hnp-Au.

    Movie S1. 3D printing Ag-Au inks to pattern a lattice structure.

    References (4043)

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Rheology of the Ag and Au starting materials and composite inks.
    • Fig. S2. Ligament size distribution.
    • Fig. S3. Nyquist plot of np-Au and 3DP-hnp-Au at open-circuit potential.
    • Fig. S4. Computational fluid dynamics (CFD) simulation of the velocity field of a square duct with a square orifice.
    • Fig. S5. Pressure drop calculations in the square duct.
    • Fig. S6. Methanol oxidation to methyl formate and carbon dioxide at 150°C.
    • Fig. S7. Compressive stress-strain curve of 3DP-hnp-Au.
    • Table S1. Methanol oxidation under different reaction conditions for np-Au and 3DP-hnp-Au.
    • References (4043)

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). 3D printing Ag-Au inks to pattern a lattice structure.

    Files in this Data Supplement:

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