4 Catalyst Materials for Oxygen Reduction Reaction
135
density of Fe-SPc is 7.4 times that of Fe-Pc, as shown in Fig. 4.35e-f. Fe-SPc’s high
ORR activity and stability stem from the insertion of its electron donor functional
groups and the isolation of active sites due to high steric hindrance. Robert et al.
[206] prepared CoHPX (cobalt hangman porphyrins) by a simple, fast, and highyield method, and then fixed CoHPX on multi-walled carbon nanotubes (MWCNTs)
to prepare CoHPX-MWCNTs. CoHPX-MWCNTs catalyze the reduction of O 2 to
H 2 O by a four-electron catalyst through a single co-plane center. Faubert et al. [208]
studied the catalytic process of Fe macrocyclic compounds to oxygen and found
that the simultaneous existence of Fe and N is necessary for the formation of active
center, but it is not certain whether they constitute active center. PEMFC test results
show that the open-circuit voltage of this battery is 0.926 V. At a voltage of 0.5 V
and a temperature of 50 °C, the output current density of the battery is equivalent to
1/3 of Pt, and this performance can be maintained for 300 h.
Although transition metal macrocyclic compounds have fairly good ORR activity,
their poor stability limits their application prospects of cathode catalysts in fuel cell.
In 1978, Bagotzky first proposed that non-precious metal electrocatalysts with stable
properties were prepared by treating macrocyclic compounds at high temperature
[209]. In this study, a macrocyclic compound (cobalt phthalocyanine, tetraphenylporphine, etc.) and a binder Teflon were uniformly mixed and coated on a carbon
electrode, and then an oxygen reduction reaction electrode was prepared by hightemperature treatment above 800°C in an inert atmosphere. Studies have shown that
the non-noble metal electrode exhibits high oxygen reduction activity and stability
in sulfuric acid electrolyte. After that, many research results also proved that the
proper heat-treatment process is not only conducive to the improvement of its ORR
activity, but also the stability of the catalyst has been greatly enhanced [210–213].
Gojkovics et al. [214] compared the ORR activity and stability of FeTPP/C catalysts
obtained by pyrolyzing FeTMPP–Cl (iron (III) tetramethoxyphenyl porphyrin chloride) to FeTPP/C catalysts at a temperature of 200 °C to 1000 °C. The performance
of the catalyst prepared under the conditions of 700–900 °C is the best, and the ORR
performance under alkaline conditions can be comparable to Pt/C. The improvement
of its stability makes it have a high practical application prospect. Further research
indicates that the ORR activity of Me/N/C catalysts obtained by pyrolysis depends
on different carbon sources (carbon support), nitrogen sources, metal sources, and
high-temperature treatment conditions [179, 215].
In 2009, ORR research on Me/N/C made a major breakthrough. Professor Dodelet
reported on Science that the ORR performance of Fe/N/C non-precious metal catalyst is very close to commercial Pt/C [216]. They mixed a high specific surface
area microporous carbon (BP2000), an iron source(ferrous acetate), and a pore filler
(3,4,9,10-fluorenetetracarboxylic dianhydride or 1,10-o-phenanthroline), Then treat
at high temperature in NH 3 atmosphere. Because the pore size of microporous carbon
is less than 2 nm, fillers and iron sources can form a large number of FeN 2+2 active
sites in the micropores. When performing the full-cell characterization on their ORR
performance, they found that when the cell voltage was ≥0.9 V, the best Fe/N/C
catalyst with a loading of 0.4 mg m
−2 were prepared by their method, which is
equivalent to commercial Pt/C. The best non-noble metal ORR catalyst prepared by
135
density of Fe-SPc is 7.4 times that of Fe-Pc, as shown in Fig. 4.35e-f. Fe-SPc’s high
ORR activity and stability stem from the insertion of its electron donor functional
groups and the isolation of active sites due to high steric hindrance. Robert et al.
[206] prepared CoHPX (cobalt hangman porphyrins) by a simple, fast, and highyield method, and then fixed CoHPX on multi-walled carbon nanotubes (MWCNTs)
to prepare CoHPX-MWCNTs. CoHPX-MWCNTs catalyze the reduction of O 2 to
H 2 O by a four-electron catalyst through a single co-plane center. Faubert et al. [208]
studied the catalytic process of Fe macrocyclic compounds to oxygen and found
that the simultaneous existence of Fe and N is necessary for the formation of active
center, but it is not certain whether they constitute active center. PEMFC test results
show that the open-circuit voltage of this battery is 0.926 V. At a voltage of 0.5 V
and a temperature of 50 °C, the output current density of the battery is equivalent to
1/3 of Pt, and this performance can be maintained for 300 h.
Although transition metal macrocyclic compounds have fairly good ORR activity,
their poor stability limits their application prospects of cathode catalysts in fuel cell.
In 1978, Bagotzky first proposed that non-precious metal electrocatalysts with stable
properties were prepared by treating macrocyclic compounds at high temperature
[209]. In this study, a macrocyclic compound (cobalt phthalocyanine, tetraphenylporphine, etc.) and a binder Teflon were uniformly mixed and coated on a carbon
electrode, and then an oxygen reduction reaction electrode was prepared by hightemperature treatment above 800°C in an inert atmosphere. Studies have shown that
the non-noble metal electrode exhibits high oxygen reduction activity and stability
in sulfuric acid electrolyte. After that, many research results also proved that the
proper heat-treatment process is not only conducive to the improvement of its ORR
activity, but also the stability of the catalyst has been greatly enhanced [210–213].
Gojkovics et al. [214] compared the ORR activity and stability of FeTPP/C catalysts
obtained by pyrolyzing FeTMPP–Cl (iron (III) tetramethoxyphenyl porphyrin chloride) to FeTPP/C catalysts at a temperature of 200 °C to 1000 °C. The performance
of the catalyst prepared under the conditions of 700–900 °C is the best, and the ORR
performance under alkaline conditions can be comparable to Pt/C. The improvement
of its stability makes it have a high practical application prospect. Further research
indicates that the ORR activity of Me/N/C catalysts obtained by pyrolysis depends
on different carbon sources (carbon support), nitrogen sources, metal sources, and
high-temperature treatment conditions [179, 215].
In 2009, ORR research on Me/N/C made a major breakthrough. Professor Dodelet
reported on Science that the ORR performance of Fe/N/C non-precious metal catalyst is very close to commercial Pt/C [216]. They mixed a high specific surface
area microporous carbon (BP2000), an iron source(ferrous acetate), and a pore filler
(3,4,9,10-fluorenetetracarboxylic dianhydride or 1,10-o-phenanthroline), Then treat
at high temperature in NH 3 atmosphere. Because the pore size of microporous carbon
is less than 2 nm, fillers and iron sources can form a large number of FeN 2+2 active
sites in the micropores. When performing the full-cell characterization on their ORR
performance, they found that when the cell voltage was ≥0.9 V, the best Fe/N/C
catalyst with a loading of 0.4 mg m
−2 were prepared by their method, which is
equivalent to commercial Pt/C. The best non-noble metal ORR catalyst prepared by