Research ArticleMATERIALS SCIENCE

Exceptional oxygen evolution reactivities on CaCoO3 and SrCoO3

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Science Advances  09 Aug 2019:
Vol. 5, no. 8, eaav6262
DOI: 10.1126/sciadv.aav6262
  • Fig. 1 The structure of ACoO3 (A = Ca, Sr).

    (A) Observed, calculated, and difference patterns for the Rietveld refinement from the XRD of cubic ACoO3. a.u., arbitrary units. (B and C) TEM images of ACoO3 (A = Ca, Sr).

  • Fig. 2 OER performance of ACoO3 (A = Ca, Sr), RuO2, LaCoO3, and Co3O4.

    (A) Linear sweep voltammograms at 1600 rpm in 0.1 M KOH. (B) Overpotential required at 10 mA cm−2. (C) Tafel slopes. (D) Chronoamperometric curves in an O2-saturated 0.1 M KOH electrolyte at 1.6 V versus RHE.

  • Fig. 3 Magnetic and transport properties of ACoO3 (A = Ca, Sr).

    (A) Temperature dependence of resistivity measured at zero field [CaCoO3 (red curve), SrCoO3 (blue curve digitized from (20)] temperature dependence of magnetization in both zero-field cooling (ZFC) and field cooling (FC). (B) Electronic spin states of the octahedral site Co ions of ACoO3 (A = Ca, Sr) and Co3O4. (C) Schematic band diagrams of ACoO3 (A = Ca, Sr). IS, intermediate spin.

  • Fig. 4 OER performance of ACoO3 (A = Ca, Sr) in alkaline solutions with different pH.

    (A to D) CV measurements in O2-saturated KOH with pH 12.5 to 14, showing the pH-dependent OER activity of ACoO3 (A = Ca, Sr) on the RHE scale.

  • Fig. 5 The durability of ACoO3 (A = Ca, Sr).

    (A to D) XRD, Raman spectra, and TEM results of ACoO3 (A = Ca, Sr) after OER testing.

  • Fig. 6 Possible OER mechanisms in ACoO3 (A = Ca, Sr).

    (A) Conventional OER mechanism involving four proton-electron transfer steps on the active surface metal sites. (B) OER mechanism with surface lattice oxygen activated for OER to form peroxide and evolve O2. (C and D) Two proposed OER mechanisms based on the Co4+─O2− bond; the deprotonation process by OH is finished by a chemical step (step 5) rather than a proton/electron-coupled transfer step.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaav6262/DC1

    Fig. S1. SEM images and particle size distribution of CaCoO3 and SrCoO3.

    Fig. S2. Elemental distribution of CaCoO3 and SrCoO3.

    Fig. S3. CV curves of Co-based catalysts.

    Fig. S4. Double-layer capacitance measurement to determine the electrochemically active surface area of CaCoO3 and RuO2.

    Fig. S5. The impedance plots and cycling stability of the catalysts studied in this work.

    Fig. S6. Response of charge transfer resistance (Rct) to applied potential of the catalysts studied in this work to applied potential in the solution of pH 12.5, 13, 13.5, and 14.

    Fig. S7. The intermediate spin state of CoIII in LaCoO3 (t4e1, S = 1) at 25°C.

    Fig. S8. pH-dependent OER activity of RuO2 in O2-saturated KOH with pH 12.5 to 14.

    Table S1. Structural refinements of CaCoO3 and SrCoO3 obtained at room temperature.

    Table S2. OER activity and ECSA of all studied catalysts.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. SEM images and particle size distribution of CaCoO3 and SrCoO3.
    • Fig. S2. Elemental distribution of CaCoO3 and SrCoO3.
    • Fig. S3. CV curves of Co-based catalysts.
    • Fig. S4. Double-layer capacitance measurement to determine the electrochemically active surface area of CaCoO3 and RuO2.
    • Fig. S5. The impedance plots and cycling stability of the catalysts studied in this work.
    • Fig. S6. Response of charge transfer resistance (Rct) to applied potential of the catalysts studied in this work to applied potential in the solution of pH 12.5, 13, 13.5, and 14.
    • Fig. S7. The intermediate spin state of CoIII in LaCoO3 (t4e1, S = 1) at 25°C.
    • Fig. S8. pH-dependent OER activity of RuO2 in O2-saturated KOH with pH 12.5 to 14.
    • Table S1. Structural refinements of CaCoO3 and SrCoO3 obtained at room temperature.
    • Table S2. OER activity and ECSA of all studied catalysts.

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