Research ArticleELECTRICAL ENGINEERING

Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting

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Science Advances  18 Nov 2016:
Vol. 2, no. 11, e1600690
DOI: 10.1126/sciadv.1600690
  • Fig. 1 Schematic of applications of PEMECs and PEM fuel cells coupled with sustainable energy sources.
  • Fig. 2 Microscale electrochemical reactions in PEMECs.

    (A) Front-view image of electrochemical reactions in the PEMEC microchannel (movie S1). (B) Triangular opening (600 μm; movie S2). (C) Triangular opening (400 μm; movie S3). (D) Circular opening (500 μm; movie S4). (E) Circular opening (50 μm; movie S5).

  • Fig. 3 Schematic of opening-scale electrochemical reactions occurring in the anode of a PEMEC.

    (A) True electrochemical reaction phenomena as revealed in this study. (B) Conventional perception of electrochemical reactions. (C) TPB electrochemical reaction. (D) Phenomena demonstrated in preclusive experiments described in this paper [white wire, thin tungsten wire as conductive material (movie S6); yellow wire, plastic microfiber as nonconductive material (movie S7)]. (E) Suggested future design for CLs in PEMECs: the catalyst is only deposited on the lands of LGDLs.

  • Fig. 4 Comparison of different catalyst loading methods and substrates in the cathode of a PEMEC (one is on the membrane and the other one is on the LGDL).

    (A) Schematic of an LGDL and a conventional catalyst-coated membrane (CCM). (B) Schematic of a catalyst sputter-coated on LGDL. (C) Secondary electron scanning transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy (inset) images of a catalyst structure on a conventional CCM. (D) Secondary electron scanning transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy (inset) images of a catalyst sputter-coated on LGDL. (E) Performance comparison of cells with a conventional CCM and a catalyst sputter-coated on LGDL. (F) Comparison of mass activities of the catalyst between a conventional CCM and a sputter-coated catalyst on LGDL.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/11/e1600690/DC1

    Sequence of photos of electrochemical reactions in PEMEC micro-openings

    Preliminary results for the new catalyst fabrication method

    fig. S1. Schematic of a PEMEC.

    fig. S2. Schematic of the transparent, reaction-visible PEMEC and LGDLs with highly tunable and straight holes throughout.

    fig. S3. Schematic of a developed nanofabrication process for the titanium thin LGDL with highly tunable micro-openings.

    fig. S4. A sequence images of electrochemical reactions in a triangle micro-opening of the thin, highly tunable titanium LGDL.

    movie S1. Phenomena of electrochemical reaction occurring at microchannel scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; channel size, 1 mm height; triangle opening size, 600 μm; duration, 0.058 s).

    movie S2. Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 600 μm; duration, 0.058 s).

    movie S3. Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 400 μm; duration, 0.069 s).

    movie S4. Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; circular opening size, 500 μm; duration, 0.121 s).

    movie S5. Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; circular opening size, 50 μm; duration, 0.112 s).

    movie S6. Phenomena of electrochemical reaction occurring in a triangle opening with a thin tungsten wire as conductive wire (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 600 μm).

    movie S7. Phenomena of electrochemical reaction occurring in a triangle opening with a plastic microfiber as nonconductive wire (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 600 μm).

  • Supplementary Materials

    This PDF file includes:

    • Sequence of photos of electrochemical reactions in PEMEC micro-openings
    • Preliminary results for the new catalyst fabrication method
    • fig. S1. Schematic of a PEMEC.
    • fig. S2. Schematic of the transparent, reaction-visible PEMEC and LGDLs with well-tunable and straight holes throughout.
    • fig. S3. Schematic of a developed nanofabrication process for the titanium thin LGDL with well-tunable micro-openings.
    • fig. S4. A sequence images of electrochemical reactions in a triangle micro-opening of the thin, highly tunable titanium LGDL.
    • Legends for movies S1 to S7

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). Phenomena of electrochemical reaction occurring at microchannel scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; channel size, 1 mm height; triangle opening size, 600 μm; duration, 0.058 s).
    • movie S2 (.avi format). Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 600 μm; duration, 0.058 s).
    • movie S3 (.avi format). Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 400 μm; duration, 0.069 s).
    • movie S4 (.avi format). Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; circular opening size, 500 μm; duration, 0.121 s).
    • movie S5 (.avi format). Phenomena of electrochemical reaction occurring at micro-opening scale (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; circular opening size, 50 μm; duration, 0.112 s.
    • movie S6 (.avi format). Phenomena of electrochemical reaction occurring in a triangle opening with a thin tungsten wire as conductive wire (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 600 μm).
    • movie S7 (.avi format). Phenomena of electrochemical reaction occurring in a triangle opening with a plastic microfiber as nonconductive wire (operation current density, 2 A/cm2; DI water flow rate, 20 ml/min; triangular opening size, 600 μm).

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