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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.


C 1s HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. (c) Plot of FWHM of C 1s HXPES spectra as a function of pyrolysis temperature.
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Fig5: C 1s HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. (c) Plot of FWHM of C 1s HXPES spectra as a function of pyrolysis temperature.

Mentions: Figure 5a,b shows the C 1s HXPES spectra of the FePc/PhRs and HB-FePc catalysts, respectively. All of the pyrolyzed samples show a single peak in the range from 284.3 to 284.9 eV, indicating that the catalysts predominantly consist of typical sp2 carbon networks [7,10,28,29]. The FePc/PhRs precursor shows two main peaks at 284.9 and 286.2 eV corresponding to C-C and C-N bonds, respectively, and a small shake-up satellite at 288.1 eV (the same profile as in ref. [30]). The full width at half-maximum (FWHM) of the single peak was estimated by a rough fitting with a single Voigt function, which can be used to represent the degree of sp2 carbon network formation [28,29]; i.e., a smaller FWHM indicates more development of the sp2 carbon network. Figure 5c plots the FWHM of the single peak as a function of pyrolysis temperature. For the FePc/PhRs catalysts, the FWHMs increase by 0.2 eV from 550°C to 600°C, indicating decomposition of the Fe-N4 centers of FePc [7,14] and appearance of disordered carbon structure. In contrast, the FWHMs of the HB-FePc catalysts exhibit a very slight (0.02 eV) increase from 550°C to 600°C, suggesting that the HB-FePc catalysts do not decompose or graphitize as much as the FePc/PhRs catalysts in this temperature range because of their higher thermostability. Details of the correlation between the active site formation mechanism and carbon structure of these catalysts will be discussed in the last section.Figure 5


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)

C 1s HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. (c) Plot of FWHM of C 1s HXPES spectra as a function of pyrolysis temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401482&req=5

Fig5: C 1s HXPES spectra. (a) FePc/PhRs and (b) HB-FePc catalysts. (c) Plot of FWHM of C 1s HXPES spectra as a function of pyrolysis temperature.
Mentions: Figure 5a,b shows the C 1s HXPES spectra of the FePc/PhRs and HB-FePc catalysts, respectively. All of the pyrolyzed samples show a single peak in the range from 284.3 to 284.9 eV, indicating that the catalysts predominantly consist of typical sp2 carbon networks [7,10,28,29]. The FePc/PhRs precursor shows two main peaks at 284.9 and 286.2 eV corresponding to C-C and C-N bonds, respectively, and a small shake-up satellite at 288.1 eV (the same profile as in ref. [30]). The full width at half-maximum (FWHM) of the single peak was estimated by a rough fitting with a single Voigt function, which can be used to represent the degree of sp2 carbon network formation [28,29]; i.e., a smaller FWHM indicates more development of the sp2 carbon network. Figure 5c plots the FWHM of the single peak as a function of pyrolysis temperature. For the FePc/PhRs catalysts, the FWHMs increase by 0.2 eV from 550°C to 600°C, indicating decomposition of the Fe-N4 centers of FePc [7,14] and appearance of disordered carbon structure. In contrast, the FWHMs of the HB-FePc catalysts exhibit a very slight (0.02 eV) increase from 550°C to 600°C, suggesting that the HB-FePc catalysts do not decompose or graphitize as much as the FePc/PhRs catalysts in this temperature range because of their higher thermostability. Details of the correlation between the active site formation mechanism and carbon structure of these catalysts will be discussed in the last section.Figure 5

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.