131
which corresponds to approximately 2–4 monolayers of Pt. A two-dimensional
image overlapping Fe EELS signals (blue) on Pt signals (red)) also clearly demonstrates the formation of core-shell structure with Pt shell on PtFe core (Fig. 8.22b).
Segregation of Pt on the surfaces takes place while Fe nitride cores are formed during thermal annealing in NH 3 as the nitrogen precursor [39].
A PtFeN catalyst is composed of Pt shell with a core of Fe 4 N nitride, in which Fe
atoms are partially substituted by Pt. The PtFeN/C catalyst structure is analogous
with the PtNiN catalyst, which consists of Ni 4 N-based core and 2–4 monolayerthick Pt shell. The X-Ray diffraction (XRD) pattern from PtCoN/C shows three
major peaks shifted to higher angles compared with those of PtFeN/C. This is
caused by greater contraction in the Pt-Pt bonds on the Co nitride cores.
The half-wave potential of 892 mV for the PtFeN core-shell catalyst is 42 mV
higher than that of Pt/C catalyst. The kinetic currents, for PtFeN/C and PtCoN/C
catalysts show 3–4 times higher mass activities and 3–7 times higher specific activities than those of Pt/C.
The long-term ORR polarization curve shows only a 5 mV decrease in its halfwave potential, and the voltammetry exhibited nearly no loss in hydrogen adsorption/
1 2 3 4 5 6 7 8
Distance (nm)
Normalized intensity (a.u.)
Pt
Pt
Ni
Ni
(C)
(b)
(a)
5 nm
2 n m
Fig. 8.20 (a) HAADF-STEM image of a PtNiN core–shell nanoparticle with its corresponding
two-dimensional EELS mapping of Pt M and Ni L signals (dotted lines for visualization purpose
only). (b) STEM image of PtNiN core–shell nanoparticles. (c) EELS line-scan profiles of Pt and
Ni in a single nanoparticle along with schematic representation of a single PtNiN nanoparticle
(blue, Pt; gray, Ni; purple, N) [40]. Reproduced with permission with American Chemical Society
8.1 Oxygen Reduction Reaction (ORR)
which corresponds to approximately 2–4 monolayers of Pt. A two-dimensional
image overlapping Fe EELS signals (blue) on Pt signals (red)) also clearly demonstrates the formation of core-shell structure with Pt shell on PtFe core (Fig. 8.22b).
Segregation of Pt on the surfaces takes place while Fe nitride cores are formed during thermal annealing in NH 3 as the nitrogen precursor [39].
A PtFeN catalyst is composed of Pt shell with a core of Fe 4 N nitride, in which Fe
atoms are partially substituted by Pt. The PtFeN/C catalyst structure is analogous
with the PtNiN catalyst, which consists of Ni 4 N-based core and 2–4 monolayerthick Pt shell. The X-Ray diffraction (XRD) pattern from PtCoN/C shows three
major peaks shifted to higher angles compared with those of PtFeN/C. This is
caused by greater contraction in the Pt-Pt bonds on the Co nitride cores.
The half-wave potential of 892 mV for the PtFeN core-shell catalyst is 42 mV
higher than that of Pt/C catalyst. The kinetic currents, for PtFeN/C and PtCoN/C
catalysts show 3–4 times higher mass activities and 3–7 times higher specific activities than those of Pt/C.
The long-term ORR polarization curve shows only a 5 mV decrease in its halfwave potential, and the voltammetry exhibited nearly no loss in hydrogen adsorption/
1 2 3 4 5 6 7 8
Distance (nm)
Normalized intensity (a.u.)
Pt
Pt
Ni
Ni
(C)
(b)
(a)
5 nm
2 n m
Fig. 8.20 (a) HAADF-STEM image of a PtNiN core–shell nanoparticle with its corresponding
two-dimensional EELS mapping of Pt M and Ni L signals (dotted lines for visualization purpose
only). (b) STEM image of PtNiN core–shell nanoparticles. (c) EELS line-scan profiles of Pt and
Ni in a single nanoparticle along with schematic representation of a single PtNiN nanoparticle
(blue, Pt; gray, Ni; purple, N) [40]. Reproduced with permission with American Chemical Society
8.1 Oxygen Reduction Reaction (ORR)