Photochemical Route for Accessing Amorphous Metal Oxide Materials for Water Oxidation Catalysis

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Science  05 Apr 2013:
Vol. 340, Issue 6128, pp. 60-63
DOI: 10.1126/science.1233638

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  1. Fig. 1

    SEM cross-section and top-down surface images of a-Fe2O3 films prepared by PMOD, followed by a 1-hour annealing step in air at Tanneal = 100°, 400°, or 600°C.

  2. Fig. 2

    XRD powder patterns acquired on as-prepared (i.e., no annealing step) and annealed (Tanneal indicated) Fe2O3 films. Bragg reflections for hematite are observed for films annealed at Tanneal > 500°C). Patterns for hematite [Joint Committee on Powder Diffraction Standards (JCPDS) card 33-664] and SnO2 (JCPDS card 41-1445) are also shown.

  3. Fig. 3

    Electrochemical behavior for oxide thin films prepared from 15% w/w precursor solutions by the PMOD technique, followed by annealing at 100°C. (A) Cyclic voltammograms for films of a-Fe2O3 (blue) and hematite (gray), and a blank fluorine-doped tin oxide (FTO) substrate. (B) Tafel plot showing the higher catalytic activity of a-Fe2O3 relative to hematite. Comparison of electrochemical behavior for thin films of a-Fe2O3, a-Fe50Ni50Ox, a-Fe50Co50Ox, and a-Fe33Co33Ni33Ox films: (C) cyclic voltammograms; (D) Tafel plots; (E) onset potentials (Ecat) and potentials required to reach j = 0.5 mA cm−2; and (F) Tafel slopes for the various catalyst films. Electrochemistry conditions: counterelectrode = Pt mesh; reference electrode = Ag/AgCl, KCl(sat’d); scan rate = 10 mV s−1; electrolyte = 0.1 M KOH(aq); current densities were corrected for uncompensated resistance. Dashed red lines correspond to the thermodynamic potential for water oxidation (26). Error bars indicate the SD between multiple electrodes (three minimum).