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Active site formation mechanism of carbon-based oxygen reduction catalysts derived from a hyperbranched iron phthalocyanine polymer.

Hiraike Y, Saito M, Niwa H, Kobayashi M, Harada Y, Oshima M, Kim J, Nabae Y, Kakimoto MA - Nanoscale Res Lett (2015)

Bottom Line: The properties of the HB-FePc catalyst are compared with those of a catalyst with high oxygen reduction reaction (ORR) activity synthesized from a mixture of iron phthalocyanine and phenolic resin (FePc/PhRs).Electrochemical measurements demonstrate that the HB-FePc catalyst does not lose its ORR activity up to 900°C, whereas that of the FePc/PhRs catalyst decreases above 700°C.Consequently, effective doping of active nitrogen species into the sp (2) carbon network of the HB-FePc catalysts may occur up to 900°C.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan ; Current address: Toray Industries, Incorporated, Nihonbashi-Muromachi 2-chome, Tokyo, Japan.

ABSTRACT
Carbon-based cathode catalysts derived from a hyperbranched iron phthalocyanine polymer (HB-FePc) were characterized, and their active-site formation mechanism was studied by synchrotron-based spectroscopy. The properties of the HB-FePc catalyst are compared with those of a catalyst with high oxygen reduction reaction (ORR) activity synthesized from a mixture of iron phthalocyanine and phenolic resin (FePc/PhRs). Electrochemical measurements demonstrate that the HB-FePc catalyst does not lose its ORR activity up to 900°C, whereas that of the FePc/PhRs catalyst decreases above 700°C. Hard X-ray photoemission spectra reveal that the HB-FePc catalysts retain more nitrogen components than the FePc/PhRs catalysts between pyrolysis temperatures of 600°C and 800°C. This is because the linked structure of the HB-FePc precursor has high thermostability against nitrogen desorption. Consequently, effective doping of active nitrogen species into the sp (2) carbon network of the HB-FePc catalysts may occur up to 900°C.

No MeSH data available.


Fe 2p HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. Solid, dashed, and dotted lines show the binding energies of Fe metal, Fe2+, and Fe3+, respectively. The arrows indicate satellite peaks of Fe2O3 2p3/2 and 2p1/2, which emerge approximately 8 eV above pristine peaks [31]. In the spectrum of the FePc/PhRs precursor, a peak from In 3p1/2 is observed.
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Fig6: Fe 2p HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. Solid, dashed, and dotted lines show the binding energies of Fe metal, Fe2+, and Fe3+, respectively. The arrows indicate satellite peaks of Fe2O3 2p3/2 and 2p1/2, which emerge approximately 8 eV above pristine peaks [31]. In the spectrum of the FePc/PhRs precursor, a peak from In 3p1/2 is observed.

Mentions: Fe 2p HXPES spectra of the FePc/PhRs and HB-FePc catalysts are illustrated in Figure 6. Solid, dashed, and dotted lines show the binding energies of Fe metal (706.5 and 719.7 eV), FeO (709.6 and 722.9 eV), and Fe2O3 (711.6 and 725.1 eV), respectively [31]. The FePc/PhRs precursor shows two peaks at 709.5 and 723.0 eV. These values are about 1 eV higher than those reported previously for FePc (708.8 eV at Fe 2p3/2) [30,32] and similar to those of FeO. However, because we did not observe Fe oxides in the XRD pattern of the FePc/PhRs precursor (see Figure 4), the 1 eV shift could be caused by a chemical interaction between PhRs and FePc. In both catalysts pyrolyzed below 600°C, the main iron components are oxidized species. The peaks in the spectrum of Fe600 correspond to a mixture of FePc and Fe metal. In contrast, the peaks in the spectra of HB550 and HB600 can be mostly assigned to Fe2O3, consistent with the XRD results as already discussed. Reduced Fe metal peaks appear in the spectra of the HB-FePc catalysts pyrolyzed at temperatures at least 50°C higher than the FePc/PhRs catalysts, in good agreement with the XRD results. In both catalysts, the oxidized moieties are completely reduced to a metallic state (Fe°) at higher pyrolysis temperatures.Figure 6


Active site formation mechanism of carbon-based oxygen reduction catalysts derived from a hyperbranched iron phthalocyanine polymer.

Hiraike Y, Saito M, Niwa H, Kobayashi M, Harada Y, Oshima M, Kim J, Nabae Y, Kakimoto MA - Nanoscale Res Lett (2015)

Fe 2p HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. Solid, dashed, and dotted lines show the binding energies of Fe metal, Fe2+, and Fe3+, respectively. The arrows indicate satellite peaks of Fe2O3 2p3/2 and 2p1/2, which emerge approximately 8 eV above pristine peaks [31]. In the spectrum of the FePc/PhRs precursor, a peak from In 3p1/2 is observed.
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Related In: Results  -  Collection

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Fig6: Fe 2p HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. Solid, dashed, and dotted lines show the binding energies of Fe metal, Fe2+, and Fe3+, respectively. The arrows indicate satellite peaks of Fe2O3 2p3/2 and 2p1/2, which emerge approximately 8 eV above pristine peaks [31]. In the spectrum of the FePc/PhRs precursor, a peak from In 3p1/2 is observed.
Mentions: Fe 2p HXPES spectra of the FePc/PhRs and HB-FePc catalysts are illustrated in Figure 6. Solid, dashed, and dotted lines show the binding energies of Fe metal (706.5 and 719.7 eV), FeO (709.6 and 722.9 eV), and Fe2O3 (711.6 and 725.1 eV), respectively [31]. The FePc/PhRs precursor shows two peaks at 709.5 and 723.0 eV. These values are about 1 eV higher than those reported previously for FePc (708.8 eV at Fe 2p3/2) [30,32] and similar to those of FeO. However, because we did not observe Fe oxides in the XRD pattern of the FePc/PhRs precursor (see Figure 4), the 1 eV shift could be caused by a chemical interaction between PhRs and FePc. In both catalysts pyrolyzed below 600°C, the main iron components are oxidized species. The peaks in the spectrum of Fe600 correspond to a mixture of FePc and Fe metal. In contrast, the peaks in the spectra of HB550 and HB600 can be mostly assigned to Fe2O3, consistent with the XRD results as already discussed. Reduced Fe metal peaks appear in the spectra of the HB-FePc catalysts pyrolyzed at temperatures at least 50°C higher than the FePc/PhRs catalysts, in good agreement with the XRD results. In both catalysts, the oxidized moieties are completely reduced to a metallic state (Fe°) at higher pyrolysis temperatures.Figure 6

Bottom Line: The properties of the HB-FePc catalyst are compared with those of a catalyst with high oxygen reduction reaction (ORR) activity synthesized from a mixture of iron phthalocyanine and phenolic resin (FePc/PhRs).Electrochemical measurements demonstrate that the HB-FePc catalyst does not lose its ORR activity up to 900°C, whereas that of the FePc/PhRs catalyst decreases above 700°C.Consequently, effective doping of active nitrogen species into the sp (2) carbon network of the HB-FePc catalysts may occur up to 900°C.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan ; Current address: Toray Industries, Incorporated, Nihonbashi-Muromachi 2-chome, Tokyo, Japan.

ABSTRACT
Carbon-based cathode catalysts derived from a hyperbranched iron phthalocyanine polymer (HB-FePc) were characterized, and their active-site formation mechanism was studied by synchrotron-based spectroscopy. The properties of the HB-FePc catalyst are compared with those of a catalyst with high oxygen reduction reaction (ORR) activity synthesized from a mixture of iron phthalocyanine and phenolic resin (FePc/PhRs). Electrochemical measurements demonstrate that the HB-FePc catalyst does not lose its ORR activity up to 900°C, whereas that of the FePc/PhRs catalyst decreases above 700°C. Hard X-ray photoemission spectra reveal that the HB-FePc catalysts retain more nitrogen components than the FePc/PhRs catalysts between pyrolysis temperatures of 600°C and 800°C. This is because the linked structure of the HB-FePc precursor has high thermostability against nitrogen desorption. Consequently, effective doping of active nitrogen species into the sp (2) carbon network of the HB-FePc catalysts may occur up to 900°C.

No MeSH data available.