Research ArticleELECTROCHEMISTRY

A physical catalyst for the electrolysis of nitrogen to ammonia

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Science Advances  27 Apr 2018:
Vol. 4, no. 4, e1700336
DOI: 10.1126/sciadv.1700336
  • Fig. 1 Aberration-corrected scanning transmission electron microscopy (STEM) images of CNSs.

    (A) The pristine nanospikes exhibit layers of folded graphene with some structural disorder due to nitrogen incorporation in the basal plane. (B) O-etched CNS retains the layered graphene structure but exhibits a much larger radius at the tip, thereby lowering the local electric field present at the tips.

  • Fig. 2 The partial current densities and formation rate of ammonia normalized by the ECSA at various potentials in a range from −1.29 to −0.79 V using 0.25 M LiClO4 electrolyte.

    (A) The CNS electrode in the presence of N2 produced significant ammonia compared to O-etched CNS and glassy carbon controls or to an argon gas experiment, which produced no ammonia. The formation rate increased to −1.19 V, above which hydrogen formation outcompeted ammonia formation. The partial current densities and formation rate of ammonia were normalized by the ECSA. (B) The Faradaic efficiencies reflect the formation rates, with the highest efficiency of 11.56 ± 0.85% at −1.19 V. For both (A) and (B), error bars represent the SD of all measurements at that potential.

  • Fig. 3 Comparison of electrolyte counterion effect of Li+ (gray), Na+ (red), and K+ (blue).

    (A) The formation rate and partial current density are in the order of Li+ > Na+ > K+. (B) FE follows the same order of Li+ > Na+ > K+. Data are shown for polarization potentials at −1.19, −0.99, and −0.79 V versus RHE.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/e1700336/DC1

    Modeling and simulation details

    table S1. Elemental analysis of C, N, O, and Si in original CNS, O-etched CNS, and glassy carbon by energy dispersive x-ray spectrometry elemental mapping.

    table S2. Partial current densities (mA cm−2) for CNS, oxygen-etched CNS, glassy carbon, and CNS with argon gas.

    table S3. Comparison of open-circuit potentials and polarizations of original CNS, O-etched CNS, and glassy carbon in 0.25 M KClO4.

    fig. S1. Representative TEM images of the CNS electrode.

    fig. S2. The variation of surface electric field Es calculated along the normal direction at the tip of a CNS for different tip radii in the case of desolvated Li+ counterion and of solvated Li+ counterion.

    fig. S3. Molecular dynamics simulation of electric double layers near a carbon nanosphere immersed in LiCl solution.

    fig. S4. Regression curves for ammonia quantification.

    fig. S5. SEM micrographs of CNS surface.

    fig. S6. SEM micrographs for the side view of CNS.

    fig. S7. XPS spectra of CNS.

    fig. S8. The overall current density (red curve) and formation rate (blue dots) with time at −1.19 V versus RHE.

    fig. S9. CP experiment to investigate stability of the electrode during the initial 5 hours of the reaction, using a larger (4.8 cm2) electrode to observe changes with respect to electrolyte composition.

    fig. S10. Oxygen-etched CNS showing smoother texture compared to unetched CNS.

    fig. S11. Correlated orbital levels calculated for three outer valence orbitals and three virtual orbitals at the level of EPT/aug-cc-pVTZ as a function of electric field strength.

    fig. S12. Ultraviolet photoelectron spectroscopy and work functions of emersed CNS.

    fig. S13. Ultraviolet photoelectron spectroscopy of pristine, unemersed CNS.

    fig. S14. Ultraviolet photoelectron spectroscopy of O-etched CNS and glassy carbon.

    fig. S15. Mass spectra of double-silylated product for ammonia from electrochemical N2 reduction.

    fig. S16. Mass spectra of 14N and 15N products in the mass region of the molecular ion.

    References (4454)

  • Supplementary Materials

    This PDF file includes:

    • Modeling and simulation details
    • table S1. Elemental analysis of C, N, O, and Si in original CNS, O-etched CNS, and glassy carbon by energy dispersive x-ray spectrometry elemental mapping.
    • table S2. Partial current densities (mA cm−2) for CNS, oxygen-etched CNS, glassy carbon, and CNS with argon gas.
    • table S3. Comparison of open-circuit potentials and polarizations of original CNS, O-etched CNS, and glassy carbon in 0.25 M KClO4.
    • fig. S1. Representative TEM images of the CNS electrode.
    • fig. S2. The variation of surface electric field Es calculated along the normal direction at the tip of a CNS for different tip radii in the case of desolvated Li+ counterion and of solvated Li+ counterion.
    • fig. S3. Molecular dynamics simulation of electric double layers near a carbon nanosphere immersed in LiCl solution.
    • fig. S4. Regression curves for ammonia quantification.
    • fig. S5. SEM micrographs of CNS surface.
    • fig. S6. SEM micrographs for the side view of CNS.
    • fig. S7. XPS spectra of CNS.
    • fig. S8. The overall current density (red curve) and formation rate (blue dots) with time at −1.19 V versus RHE.
    • fig. S9. CP experiment to investigate stability of the electrode during the initial 5 hours of the reaction, using a larger (4.8 cm2) electrode to observe changes with respect to electrolyte composition.
    • fig. S10. Oxygen-etched CNS showing smoother texture compared to unetched CNS.
    • fig. S11. Correlated orbital levels calculated for three outer valence orbitals and three virtual orbitals at the level of EPT/aug-cc-pVTZ as a function of electric field strength.
    • fig. S12. Ultravoilet photoelectron spectroscopy and work functions of emersed CNS.
    • fig. S13. Ultraviolet photoelectron spectroscopy of pristine, unemersed CNS.
    • fig. S14. Ultraviolet photoelectron spectroscopy of O-etched CNS and glassy carbon.
    • fig. S15. Mass spectra of double-silylated product for ammonia from electrochemical N2 reduction.
    • fig. S16. Mass spectra of 14N and 15N products in the mass region of the molecular ion.
    • References (44–54)

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