Research ArticleCHEMICAL ENGINEERING

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy

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Science Advances  18 Mar 2016:
Vol. 2, no. 3, e1501602
DOI: 10.1126/sciadv.1501602
  • Fig. 1 Underpotential deposited hydrogen (Hupd) desorption peak potential as a function of pH.

    (A to D) Hupd desorption peak potentials from CVs of (A) Pt/C, (B) Ir/C, (C) Pd/C, and (D) Rh/C as a function of pH.

  • Fig. 2 Exchange current density of HOR/HER as a function of pH.

    (A to D) Exchange current densities (i0) of HOR/HER on (A) Pt/C, (B) Ir/C, (C) Pd/C, and (D) Rh/C as a function of the pH of electrolytes. HOR/HER polarization curves were measured using the RDE method in H2-saturated electrolytes at a scanning rate of 1 mV/s and a rotation speed of 1600 rpm at 293 K. Gray stars represent HOR/HER exchange current densities at 293 K estimated from the Arrhenius plot of Durst et al. (24), in which all activities were measured using an H2-pump configuration.

  • Fig. 3 Correlation between the exchange current density of HOR/HER and Hupd desorption peak potential.

    Exchange current densities of HOR/HER on Pt/C, Ir/C, Pd/C, and Rh/C as a function of the lowest underpotential-deposited hydrogen (Hupd) desorption peak potential (Epeak) from CVs. The gray dashed line represents linear fitting of all data points.

  • Fig. 4 CO onset potential as a function of pH.

    CO stripping onset potentials as a function of pH on Pt/C (magenta squares), Ir/C (red diamonds), Pd/C (olive up triangles), and Rh/C (blue down triangles).

  • Table 1 Summary of β and A.

    β and A from fitting i0 to Epeak using the expression Embedded Image, activation energy (Ea) measured using the RDE method in 0.1 M KOH from this work and an H2-pump configuration from the study of Durst et al. (24), difference in Hupd desorption peak potentials (ΔEpeak) in 0.1 M KOH and acid with pH 0, and βEa calculated as [Ea (0.1 M KOH) − Ea (H2 pump)]/FΔEpeak.

    Embedded ImageEa (kJ/mol)ΔEpeak (V)βEa
    βA0.1 M KOHH2 pump (pH 0) (24)
    Pt/C0.55929.6 ± 0.416 ± 20.170.8
    Ir/C0.86832.8 ± 0.419 ± 30.200.7
    Pd/C0.63738.9 ± 3.031 ± 20.140.6
    Rh/C0.63626.6 ± 0.728 ± 1

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/3/e1501602/DC1

    Derivation of relationship between i0 and Epeak

    Cyclic voltammograms of Pt/C, Ir/C, Pd/C, and Rh/C at different pH values

    CVs and HOR/HER polarization curves at different pH values

    Cyclic voltammograms (CVs)

    Correlation of exchange current densities with Epeak

    Arrhenius plot

    CO stripping in electrolytes with different pH values

    Effect of anions on HOR/HER activities

    TEM images of supported metal electrocatalysts

    Procedure for calculating pH for buffer solutions and comparison between calculated and experimental values

    HOR/HER polarization curves on Vulcan XC-72 in electrolytes with different pH values

    Fig. S1. CVs of Pt/C, Ir/C, Pd/C, and Rh/C at different pH values.

    Fig. S2. CVs and HOR/HER polarization curves at different pH values on Pt/C.

    Fig. S3. CVs and HOR/HER polarization curves at different pH values on Ir/C.

    Fig. S4. CVs and HOR/HER polarization curves at different pH values on Pd/C.

    Fig. S5. CVs and HOR/HER polarization curves at different pH values on Rh/C.

    Fig. S6. CVs of Pt/C, Ir/C, Pd/C, and Rh/C in 0.1 M KOH.

    Fig. S7. Correlation of exchange current densities with Epeak.

    Fig. S8. Arrhenius plots of HOR/HER activities.

    Fig. S9. CO stripping profiles on Pt/C at different pH values.

    Fig. S10. CO stripping profiles on Ir/C at different pH values.

    Fig. S11. CO stripping profiles on Pd/C at different pH values.

    Fig. S12. CO stripping profiles on Rh/C at different pH values.

    Fig. S13. Effect of anions on HOR/HER activities.

    Fig. S14. TEM images and histograms of Pt, Ir, Pd, and Rh/C.

    Fig. S15. Comparison of calculated and electrochemically measured pH of the electrolytes.

    Fig. S16. HOR/HER polarization curves on Vulcan XC-72.

    Table S1. Particle size and surface area of Pt/C, Ir/C, Pd/C, and Rh/C.

    Table S2. Effect of anions on Hupd peak potentials and HOR/HER exchange current densities.

  • Supplementary Materials

    This PDF file includes:

    • Derivation of relationship between i0 and Epeak
    • Cyclic voltammograms of Pt/C, Ir/C, Pd/C, and Rh/C at different pH values
    • CVs and HOR/HER polarization curves at different pH values
    • Cyclic voltammograms (CVs)
    • Correlation of exchange current densities with Epeak
    • Arrhenius plot
    • CO stripping in electrolytes with different pH values
    • Effect of anions on HOR/HER activities
    • TEM images of supported metal electrocatalysts
    • Procedure for calculating pH for buffer solutions and comparison between calculated and experimental values
    • HOR/HER polarization curves on Vulcan XC-72 in electrolytes with different pH values
    • Fig. S1. CVs of Pt/C, Ir/C, Pd/C, and Rh/C at different pH values.
    • Fig. S2. CVs and HOR/HER polarization curves at different pH values on Pt/C.
    • Fig. S3. CVs and HOR/HER polarization curves at different pH values on Ir/C.
    • Fig. S4. CVs and HOR/HER polarization curves at different pH values on Pd/C.
    • Fig. S5. CVs and HOR/HER polarization curves at different pH values on Rh/C.
    • Fig. S6. CVs of Pt/C, Ir/C, Pd/C, and Rh/C in 0.1 M KOH.
    • Fig. S7. Correlation of exchange current densities with Epeak.
    • Fig. S8. Arrhenius plots of HOR/HER activities.
    • Fig. S9. CO stripping profiles on Pt/C at different pH values.
    • Fig. S10. CO stripping profiles on Ir/C at different pH values.
    • Fig. S11. CO stripping profiles on Pd/C at different pH values.
    • Fig. S12. CO stripping profiles on Rh/C at different pH values.
    • Fig. S13. Effect of anions on HOR/HER activities.
    • Fig. S14. TEM images and histograms of Pt, Ir, Pd, and Rh/C.
    • Fig. S15. Comparison of calculated and electrochemically measured pH of the electrolytes.
    • Fig. S16. HOR/HER polarization curves on Vulcan XC-72.
    • Table S1. Particle size and surface area of Pt/C, Ir/C, Pd/C, and Rh/C.
    • Table S2. Effect of anions on Hupd peak potentials and HOR/HER exchange current densities.

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