6 Application of Oxygen Reduction Catalysts
217
pyridine as the precursor to prepare nitrogen-doped carbon nanocage by magnesium
oxide template method. The peak potential of oxygen reduction of nitrogen-doped
carbon nanocage in 0.1 mol/L potassium hydroxide solution was close to that of
Pt/C catalyst under the same experimental conditions. However, in acidic media, the
oxygen reduction peak potential of nitrogen-doped carbon catalyst is much lower
than that of Pt under the same experimental conditions. In 2011, Xueliang Sun’s
research group in Canada prepared nitrogen-doped carbon nanotubes (CNx) with
controllable nitrogen content by floating catalyst chemical vapor deposition [11],
nitrogen-doped carbon nanotubes (CNx) with surface nitrogen content (atomic ratio)
of 7.7 at.% have an oxygen reduction threshold potential of 0.705 V (vs. SHE) in
0.5 mol/L sulfuric acid solution saturated with oxygen. In 2014, Keiko Waki of Japan
reported that nitrogen-doped carbon nanotubes only had a peak potential of about
0.73 vs RHE in acidic media [6]. The author further pointed out that the activity was
caused by the reconstruction of carbon atoms and the formation of local defects. The
nitrogen-doped carbon nanotubes and graphene composite (NT-G) catalyst prepared
by professor Hongjie Dai of Stanford university in 2012 [12] showed a very positive peak potential in acidic media, and the peak potential of oxygen reduction was
as high as 0.89 V (vs. SHE) in 0.1 mol/L perchloric acid solution. The oxygen
reduction electrocatalytic activity of nitrogen-doped carbon materials has aroused
great interest in recent years. Researchers used a lot of experiments and theoretical
calculations to analyze the production of its catalytic activity. Some scholars believe
that carbon atoms with high positive charge are formed by doping nitrogen atoms
with strong electrophilic properties. This carbon atom can effectively bind O 2 [13,
14] through side adsorption of oxygen molecules, thus generating oxygen reduction
activity. However, there is no strong evidence on the generation of oxygen reduction
activity of nitrogen-doped carbon materials in the literature, and the real activity site
and its causes of nitrogen-doped carbon materials still need to be further studied.
Another widely studied non-noble metal catalyst for high activity oxygen reduction is transition metal/nitrogen-carbon material M-N x /C (M = Fe or Co). Early
M-N x /C catalysts were transition metal complexes of nitrogen-containing macromolecules such as phthalocyanine and porphyrin with coordination number of four
[15, 16]. The metal ions coordinate with the four nitrogen atoms in these macromolecular heterocyclic compounds to form the planar MN 4 structure (M is the transition
metal, N is the coordination nitrogen atom in the chelating heterocyclic compound),
it is generally considered as the active point of oxygen reduction in catalysts [17,
18]. However, recent studies by J. P. Dodelet showed that FeN 2 /C also has oxygen
reduction activity, and MN 2 structure may also be an oxygen reduction activity point
[17]. Therefore, the “general structural formula” of M-N x /C electrocatalyst activity
is often expressed as: M-N x /C (M refers to transition metals such as Co, Fe, Ni, etc.;
N is the nitrogen atom of the chelating agent; X = 2 or 4; C is generally sp
2 carbon).
In 1964, Jasinski [15] first discovered that phthalocyanine cobalt (CoPc) has electrocatalytic performance of oxygen reduction in alkaline solutions. In 1978, Bagotzky
et al. [19] improved the electrocatalytic activity and stability of the original M-Nx/C
catalyst in acidic solution by using high-temperature heat treatment in an inert atmosphere such as porfin and cobalt phthalocyanine. In 1989, Yeager et al. [20] prepared
217
pyridine as the precursor to prepare nitrogen-doped carbon nanocage by magnesium
oxide template method. The peak potential of oxygen reduction of nitrogen-doped
carbon nanocage in 0.1 mol/L potassium hydroxide solution was close to that of
Pt/C catalyst under the same experimental conditions. However, in acidic media, the
oxygen reduction peak potential of nitrogen-doped carbon catalyst is much lower
than that of Pt under the same experimental conditions. In 2011, Xueliang Sun’s
research group in Canada prepared nitrogen-doped carbon nanotubes (CNx) with
controllable nitrogen content by floating catalyst chemical vapor deposition [11],
nitrogen-doped carbon nanotubes (CNx) with surface nitrogen content (atomic ratio)
of 7.7 at.% have an oxygen reduction threshold potential of 0.705 V (vs. SHE) in
0.5 mol/L sulfuric acid solution saturated with oxygen. In 2014, Keiko Waki of Japan
reported that nitrogen-doped carbon nanotubes only had a peak potential of about
0.73 vs RHE in acidic media [6]. The author further pointed out that the activity was
caused by the reconstruction of carbon atoms and the formation of local defects. The
nitrogen-doped carbon nanotubes and graphene composite (NT-G) catalyst prepared
by professor Hongjie Dai of Stanford university in 2012 [12] showed a very positive peak potential in acidic media, and the peak potential of oxygen reduction was
as high as 0.89 V (vs. SHE) in 0.1 mol/L perchloric acid solution. The oxygen
reduction electrocatalytic activity of nitrogen-doped carbon materials has aroused
great interest in recent years. Researchers used a lot of experiments and theoretical
calculations to analyze the production of its catalytic activity. Some scholars believe
that carbon atoms with high positive charge are formed by doping nitrogen atoms
with strong electrophilic properties. This carbon atom can effectively bind O 2 [13,
14] through side adsorption of oxygen molecules, thus generating oxygen reduction
activity. However, there is no strong evidence on the generation of oxygen reduction
activity of nitrogen-doped carbon materials in the literature, and the real activity site
and its causes of nitrogen-doped carbon materials still need to be further studied.
Another widely studied non-noble metal catalyst for high activity oxygen reduction is transition metal/nitrogen-carbon material M-N x /C (M = Fe or Co). Early
M-N x /C catalysts were transition metal complexes of nitrogen-containing macromolecules such as phthalocyanine and porphyrin with coordination number of four
[15, 16]. The metal ions coordinate with the four nitrogen atoms in these macromolecular heterocyclic compounds to form the planar MN 4 structure (M is the transition
metal, N is the coordination nitrogen atom in the chelating heterocyclic compound),
it is generally considered as the active point of oxygen reduction in catalysts [17,
18]. However, recent studies by J. P. Dodelet showed that FeN 2 /C also has oxygen
reduction activity, and MN 2 structure may also be an oxygen reduction activity point
[17]. Therefore, the “general structural formula” of M-N x /C electrocatalyst activity
is often expressed as: M-N x /C (M refers to transition metals such as Co, Fe, Ni, etc.;
N is the nitrogen atom of the chelating agent; X = 2 or 4; C is generally sp
2 carbon).
In 1964, Jasinski [15] first discovered that phthalocyanine cobalt (CoPc) has electrocatalytic performance of oxygen reduction in alkaline solutions. In 1978, Bagotzky
et al. [19] improved the electrocatalytic activity and stability of the original M-Nx/C
catalyst in acidic solution by using high-temperature heat treatment in an inert atmosphere such as porfin and cobalt phthalocyanine. In 1989, Yeager et al. [20] prepared