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advances.sciencemag.org/cgi/content/full/4/3/eaap7970/DC1
Supplementary Materials for
In situ formation of molecular Ni-Fe active sites on heteroatom-doped
graphene as a heterogeneous electrocatalyst toward oxygen evolution
Jiong Wang, Liyong Gan, Wenyu Zhang, Yuecheng Peng, Hong Yu, Qingyu Yan, Xinghua Xia, Xin Wang
Published 9 March 2018, Sci. Adv. 4, eaap7970 (2018)
DOI: 10.1126/sciadv.aap7970
This PDF file includes:
fig. S1. High-resolution TEM images of HG-Ni.
fig. S2. SEM image of HG-Ni with EDX analysis.
fig. S3. TEM image of HG-Ni with EDX analysis.
fig. S4. FTIR spectra of Ni(acac)2, HG, and HG-Ni.
fig. S5. UV-visible spectra of Ni(acac)2, HG, and HG-Ni.
fig. S6. Schematic illustrations of electrochemical tests.
fig. S7. CVs of HG-NiFe in 1 M KOH before and after removal of FeCl3.
fig. S8. GC spectrum of O2 detection.
fig. S9. OER durability on HG-NiFe.
fig. S10. TEM image of HG-NiFe with EDX analysis.
fig. S11. TEM images of HG-NiFe.
fig. S12. XRD patterns of HG, HG-Ni, and HG-NiFe.
fig. S13. EDTA treatment of HG-NiFe.
fig. S14. CVs of HG in 1 M KOH containing FeCl3.
fig. S15. Comparisons of CVs of HG-NiFe and HG-Fe.
fig. S16. DFT model of Ni-Fe sites.
fig. S17. Analysis of HG-NiFe in Laviron equation.
fig. S18. Analysis of HG-NiFex in Laviron equation.
fig. S19. Analysis of HG-Ni in Laviron equation.
fig. S20. Pourbaix diagram of HG-Ni.
fig. S21. CO poisoning of HG-NiFe.
fig. S22. CV and TOF analysis of a control sample.
fig. S23. Analysis of a control sample in Laviron equation.
fig. S1. High-resolution TEM images of HG-Ni. High resolution TEM images of
HG-Ni, enlarged at the regions shown in the Fig. 1A, left.
fig. S2. SEM image of HG-Ni with EDX analysis. A SEM image of HG-Ni, and the
corresponding elemental mapping results analyzed by EDX spectrum.
fig. S3. TEM image of HG-Ni with EDX analysis. A TEM image of HG-Ni, and the
corresponding elemental mapping results by EDX analysis.
fig. S4. FTIR spectra of Ni(acac)2, HG, and HG-Ni.
fig. S5. UV-visible spectra of Ni(acac)2, HG, and HG-Ni. UV-visible spectra of
HG-Ni, HG and Ni(acac)2 collected in ethanol.
fig. S6. Schematic illustrations of electrochemical tests. Scheme illustrates the
electrochemical tests of HG-Ni performed in (A) 1 M KOH without any treatment,
corresponding to the CVs in Fig. 2A; (B) in purified 1 M KOH, a plastic vessel was
applied as the electrochemical cell, corresponding to the CVs in Fig. 2B; (C) in 1 M
KOH with addition of FeCl3, corresponding to the CVs in Fig. 2C and E.
fig. S7. CVs of HG-NiFe in 1 M KOH before and after removal of FeCl3. CVs of
HG-NiFe in 1 M KOH with the addition of 12 μM FeCl3 (black solid) and in the freshly
prepared 1 M KOH (red dashed), respectively.
fig. S8. GC spectrum of O2 detection. A representative GC spectrum for the detection
of O2 product of OER on HG-NiFe in 1 M KOH, potential: 1.58 V. Inset is the
corresponding digital photo during the OER measurement focusing on the anode.
fig. S9. OER durability on HG-NiFe. Current retention of HG-NiFe loaded on a
carbon fiber cloth in 1 M KOH at fixed potential, the initial current density was 10
mA cm-2.
fig. S10. TEM image of HG-NiFe with EDX analysis. A typical TEM image of
HG-NiFe with corresponding elemental mapping results by EDX analysis.
fig. S11. TEM images of HG-NiFe. TEM images of HG-NiFe at different
magnifications.
fig. S12. XRD patterns of HG, HG-Ni, and HG-NiFe.
fig. S13. EDTA treatment of HG-NiFe. (A) CV curves of HG-NiFe before and after
being treated with 2 mM EDTA solution for 12 h, 1 M KOH, scan rate: 50 mV s-1,
rotation rate: 2000 rpm. (B) UV-visible spectra of EDTA solution reacted with
HG-NiFe surface, Ni(acac)2, FeCl3, bulk Ni(OH)2 and Ni(OH)2 nanostructures. (C) The
electron microscopic images of Ni(OH)2 nanostructures, it showed the assembly of
nanosheets with edge sizes of about 5 nm.
fig. S14. CVs of HG in 1 M KOH containing FeCl3. (A) Scheme illustrates the
electrochemical tests of HG in 1 M KOH with the addition of FeCl3. (B) CV curves of
HG before and after addition of 12 μM FeCl3, scan rate: 50 mV s-1, rotation rate: 2000
rpm.
fig. S15. Comparisons of CVs of HG-NiFe and HG-Fe. (A) Comparisons of CVs of
HG-NiFe (up) and HG-Fe (bottom) in 1 M KOH, 50 mV s-1, 2000 rpm. (B)
Corresponding OER assessments of HG-Fe. In this control experiment, we tried to have
a rough estimation on the redox potential of Fe2+/3+ couple at the HG based environment.
The HG-Fe was synthesized using the same strategy as the synthesis of HG-Ni. Namely,
mixing the HG with 0.1 M Fe(acac)3 in DMF at 80 oC for 12 h. By such efforts, it was
still difficult to conjugate Fe3+ ions to HG as suggested by the low redox currents. But it
was found that the redox potential of Fe2+/3+ couples could be close to that of Ni2+/3+
couple. For OER, the catalytic currents on HG-Fe were very low with high
overpotentials, which could be assigned to the low coverage of electroactive Fe sites
(i.e., ~6×10-9 mol cm-2; in contrast, the electroactive Ni-Fe sites of HG-NiFe were
~2.6×10-7 mol cm-2). The HG-Fe exhibited instability that serious degradation of
anodic current was observed. We roughly estimated the TOFs of Fe site on HG-Fe at
high overpotentials based on the first LSV curves. It was found that the TOF of Fe sites
could reach 0.57 s-1 at an overpotential of 0.38 V (1.12 s-1 for HG-NiFe, and 0.18 s-1 for
HG-NiFex). Such a result might imply that the Fe sites were at least more OER active
than the Ni sites, so that it could further supply an implication that in the configurations
of Ni-Fe dual sites, the Fe sites could be more responsible for proceeding the OER
catalysis.
fig. S16. DFT model of Ni-Fe sites. A DFT calculation derived model for indicating
the formation of dual Ni-Fe clusters. The gray, white and green spheres represent C, H
and Cl atoms, respectively. The dark-blue and blue spheres represent Ni and Fe atoms
respectively.
fig. S17. Analysis of HG-NiFe in Laviron equation. (A) CVs of HG-NiFe with scan
rates from 5, 10, 20, 50, 100, 200, 300, 400, 500, 600 to 700 mV s-1, 1 M KOH. (B) The
plot of the redox peak currents densities versus the square root of scan rates. (C) The
plot of the redox peak potentials versus the logarithm of scan rates.
fig. S18. Analysis of HG-NiFex in Laviron equation. (A) CVs of HG-NiFex with scan
rates from 5, 10, 20, 50, 100, 200, 300, 400, 500, 600 to 700 mV s-1, 1 M KOH. (B) The
plot of the redox peak currents densities versus the square root of scan rates. (C) The
plot of the redox peak potentials versus the logarithm of scan rates.
fig. S19. Analysis of HG-Ni in Laviron equation. (A) CVs of HG-Ni with scan rates
from 5, 10, 20, 50, 100, 200, 300, 400, 500, 600 to 700 mV s-1, purified 1 M KOH. (B)
The plot of the redox peak currents densities versus the square root of scan rates. (C)
The plot of the redox peak potentials versus the logarithm of scan rates.
fig. S20. Pourbaix diagram of HG-Ni. Pourbaix diagram of HG-Ni collected in the
plastic cell, formal potentials of redox (E1/2) versus pH values of purified KOH
solutions.
fig. S21. CO poisoning of HG-NiFe. CV polarization curves of HG-NiFe before and
after being treated with CO for 4 h, 1 M KOH, scan rate: 50 mV s-1, rotation rate: 2000
rpm.
fig. S22. CV and TOF analysis of a control sample. (A) CVs of HG-Ni in absence of
OER polarization, 1 M KOH with the addition of 12 μM FeCl3, 50 mV s-1 scan rate,
2000 rpm. (B) LSV and TOFs, collected at the steady state, fresh 1 M KOH, 5 mV s-1
scan rate, 2000 rpm.
fig. S23. Analysis of a control sample in Laviron equation. (A) CVs of the above
steady electrode (fig. S22) with scan rates from 5, 10, 20, 50, 100, 200, 300, 400, 500,
600 to 700 mV s-1, fresh 1 M KOH. (B) The plot of the redox peak currents densities
versus the square root of scan rates. (C) The plot of the redox peak potentials versus the
logarithm of scan rates.