Research ArticleSURFACE CHEMISTRY

Near-infrared–driven decomposition of metal precursors yields amorphous electrocatalytic films

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Science Advances  06 Mar 2015:
Vol. 1, no. 2, e1400215
DOI: 10.1126/sciadv.1400215
  • Fig. 1 Scheme of NIRDD.

    The NIRDD of a metal precursor (for example, FeCl3) on a substrate [for example, fluorine-doped tin oxide–coated glass (FTO)] leads to the formation of amorphous metal oxide (a-MOx) and reduced metal (a-M) films under air and nitrogen, respectively.

  • Fig. 2 Cyclic voltammograms for a-FeOx and a-Fe.

    (A and B) Cyclic voltammograms for thin films of (A) a-FeOx and (B) a-Fe on FTO. Values indicate the sequence of the cycles that were recorded. (A) The oxidative sweep of a-FeOx leads to a sharp rise in current coincident with catalytic water oxidation, and subsequent cycles led to superimposable traces. (B) The oxidative sweep for a-Fe featured a markedly different current profile for the first cycle; however, subsequent cycles indicated that a-Fe was converted to a-FeOx upon oxidation on the basis of the superimposable scans. The differences in the reductive behavior were more stark, and the cathodic peak at −0.25 V for (A) a-FeOx was not detected for (B) a-Fe before HER catalysis, indicating a more reduced form of iron for (B). Experimental conditions: counter electrode = Pt mesh; reference electrode = Ag/AgCl, KCl (sat’d); scan rate = 10 mV s−1; electrolyte = 0.1 M KOH (aq).

  • Fig. 3 FTIR spectra for thin films of Fe(eh)3.

    (A and B) FTIR spectra for thin films of Fe(eh)3 on FTO upon exposure to NIR radiation for (A) 0 min (black) and 4, 16, 32, and 64 min (blue) in air, and (B) 0 min (black) and 60 min (blue) under nitrogen. Arrows indicate trends in the intensities of the C-H and C-O vibrational modes of 2-ethylhexanoate (8). a.u., arbitrary units.

  • Fig. 4 XPS spectra of the copper 2p3/2 region.

    (A and B) Fitting of the copper 2p3/2 region of XPS recorded on thin films of Cu(eh)2 on FTO after being subjected to the NIRDD process under (A) air and (B) nitrogen, respectively. Sums of the fitting components are indicated (red traces). Fitting of the data used center-of-gravity peaks for (A) Cu(O) (green) and Cu(OH)2 (orange), and (B) Cu(I)/Cu(0) (green). Signature copper(II) satellite peaks present in (A), but not in (B), confirm a more reduced form of the film when prepared under nitrogen. The computed baselines are indicated in blue.

  • Table 1 Benchmarked OER activities of a-MOX films.

    All potentials in this article are expressed versus a reversible hydrogen electrode (RHE).

    Sample*Onset η
    (V versus RHE)
    Tafel slope
    (mV dec−1)
    η10 mA/cm2 (V)
    This workLiterature
    a-FeOx0.33380.240.40 (16)
    a-NiOx0.21620.360.36 (15)
    a-Fe2Ni3Ox0.19340.330.35§ (15)
    a-MnOx0.220.430.51 (16)
    a-IrOx0.10450.260.26 (15)

    *Ox is broadly defined as oxo/oxyl/hydroxo.

    †Overpotential required to reach 10 mA/cm2, unless otherwise indicated, without correcting for mass transport.

    ‡Overpotential required to reach 1 mA/cm2; this value may be affected by stability issues at this pH. A Tafel slope value is not provided due to film instability under steady-state conditions.

    §Corresponds to FeNiOx.

    ¶Recorded at pH 0; all other data in table recorded at pH 13.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/2/e1400215/DC1

      Fig. S1. Temperature profiles of substrates under the NIR lamp.

      Fig. S2. UV-vis absorption spectra on amorphous films.

      Fig. S3. Diffractograms of a-FeOx and a-Fe on FTO.

      Fig. S4. Diffractograms of a-FeOx on glass.

      Fig. S5. Chronoamperometric measurements of a-FeOx.

      Fig. S6. Cyclic voltammograms for thin films of a-FeOx.

      Fig. S7. Diffractograms of thin films of a-IrOx, a-NiOx, and a-MnOx.

      Fig. S8. Cyclic voltammograms for thin films of a-IrOx, a-NiOx, and a-MnOx.

      Fig. S9. TGA and DSC profiles for FeCl3 and Fe(eh)3.

      Fig. S10. TGA and DSC profiles for FeCl3 and Fe(eh)3.

      Fig. S11. FTIR spectra of independent samples of Fe(eh)3/FTO.

      Fig. S12. FTIR spectra of thin films of Ir(acac)3/FTO, Ni(eh)2/FTO, and Mn(eh)3/FTO.

      Fig. S13. X-ray photoelectron spectra for a-FeOx and a-Fe on FTO.

      Fig. S14. X-ray photoelectron spectra detailing the Fe 2p3/2 region.

      Fig. S15. XPS data for a-CuOx and a-Cu on FTO.

      Fig. S16. Images of solid copper samples.

      Fig. S17. Diffractograms of a-CuOx and a-Cu.

      Fig. S18. FTIR spectra of Fe2Ni3(eh)3/FTO.

      Fig. S19. Diffractograms on a-Fe2Ni3Ox and a-Fe2Ni3.

      Fig. S20. Cyclic voltammograms for thin films of a-Fe2Ni3Ox and a-Fe2Ni3.

      Fig. S21. Cyclic voltammograms for thin films of a-IrOx/membrane.

      Fig. S22. FTIR spectra of Ir(acac)3/membrane.

      Table S1. Elemental analysis of amorphous metal oxide films determined by EDX.

    • Supplementary Materials

      This PDF file includes:

      • Fig. S1. Temperature profiles of substrates under the NIR lamp.
      • Fig. S2. UV-vis absorption spectra on amorphous films.
      • Fig. S3. Diffractograms of a-FeOx and a-Fe on FTO.
      • Fig. S4. Diffractograms of a-FeOx on glass.
      • Fig. S5. Chronoamperometric measurements of a-FeOx.
      • Fig. S6. Cyclic voltammograms for thin films of a-FeOx.
      • Fig. S7. Diffractograms of thin films of a-IrOx, a-NiOx, and a-MnOx.
      • Fig. S8. Cyclic voltammograms for thin films of a-IrOx, a-NiOx, and a-MnOx.
      • Fig. S9. TGA and DSC profiles for FeCl3 and Fe(eh)3.
      • Fig. S10. TGA and DSC profiles for FeCl3 and Fe(eh)3.
      • Fig. S11. FTIR spectra of independent samples of Fe(eh)3/FTO.
      • Fig. S12. FTIR spectra of thin films of Ir(acac)3/FTO, Ni(eh)2/FTO, and Mn(eh)3/FTO.
      • Fig. S13. X-ray photoelectron spectra for a-FeOx and a-Fe on FTO.
      • Fig. S14. X-ray photoelectron spectra detailing the Fe 2p3/2 region.
      • Fig. S15. XPS data for a-CuOx and a-Cu on FTO.
      • Fig. S16. Images of solid copper samples.
      • Fig. S17. Diffractograms of a-CuOx and a-Cu.
      • Fig. S18. FTIR spectra of Fe2Ni3(eh)3/FTO.
      • Fig. S19. Diffractograms on a-Fe2Ni3Ox and a-Fe2Ni3.
      • Fig. S20. Cyclic voltammograms for thin films of a-Fe2Ni3Ox and a-Fe2Ni3.
      • Fig. S21. Cyclic voltammograms for thin films of a-IrOx/membrane.
      • Fig. S22. FTIR spectra of Ir(acac)3/membrane.
      • Table S1. Elemental analysis of amorphous metal oxide films determined by EDX.

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