II International Symposium on Carbon for Catalysis ABSTRACTS

KL-2
samples have a very high specific surface area (1000-3100 m 2 /g) and a large fraction of
micropores - over 70%. The effect of the nature of the precursor and the preparation
conditions on nitrogen content and NAC properties were studied. It was shown that the BET
area and pore volume generally decrease and the N content increases with lowering of the
temperature.
The state of nitrogen species in N-doped carbon supports was studied by XPS. The
results showed that two types of N are predominant in both types of supports: with binding
energies of 398.5 eV and 400.8 eV. According to literature, these signals correspond to
pyridine-like N and bridgehead-type N incorporated into graphitic network, respectively. The
predominance of the former favors the coordination of Co ions and formation of the active
sites for oxygen reduction. In addition a weak signal at 400.0 eV was observed in NAC
samples, which may be assigned to amino or -C≡N groups.
Cobalt catalysts were prepared by treatment of suspension of NCNF or NAC in water
with cobalt acetate taken in quantity to provide 1.5% Co content in the catalyst, followed by
water evaporation, drying and subsequent heat treatment in different atmospheres (Ar or
NH 3 +H 2 +Ar) at temperatures 600 and 900°C.
TEM study revealed the presence of metal cobalt particles in the initial catalysts. There
are two groups of particles: with a size of 10-50 nm and with a size about 300 nm. After
catalyst washing with sulfuric acid, the larger particles are removed and only small cobalt
particles encapsulated into the support structure remain on the surface.
The study of the states of surface nitrogen atoms in the catalysts supported on NAC
showed that there are three types of nitrogen atoms: pyridinic-type nitrogen atoms (398.6 eV
to bridgehead-type N incorporated into graphitic network (400.9 eV) and nitrogen atoms in
the composition of amino or -C≡N groups (400.0 eV). The XPS study in the Co 2p region
showed the presence of signals belonging to Co 2+ cations bound to nitrogen and to cobalt
cations in surface cobalt oxides on metal cobalt particles.
The catalyst activity of the prepared samples with different nitrogen and cobalt contents
was studied by the method of rotating disk. It was shown that oxygen reduction activities of
the catalysts depend mostly on the N-bound cobalt content, and enhance with its increase.
Thus, the developed N-doped materials can be considered as prospective materials for
preparation of non-Pt PEFC catalysts because they contain pyridinic type N atoms capable of
binding Co 2+ and forming active sites for oxygen reduction.
Acknowledgments: The authors gratefully acknowledge the NEDO support in frame of
the project «Development of high-performance N-doped carbon materials for non-platinum
PEFC electrocatalysts” and Dr. I.Ismagilov for INTAS Young Scientist Postdoctoral
Fellowship 03-55-1568 (2004-2006).
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