4 Catalyst Materials for Oxygen Reduction Reaction
161
nitrogen content has higher oxygen reduction activity. Yang et al. [407] prepared
porous nitrogen-doped carbon with high surface area using silicon nanoparticles
as template. The specific surface area of the material reached 1500 m
2 g
−1 , and it
had narrow mesoporous distribution (12 nm), and its oxygen reduction performance
was discussed. They found that the oxygen reduction activity of these materials was
close to that of commercial Pt/C catalyst, and that the porous nitrogen-doped carbon
with high specific surface area obtained by carbonizing base materials had better
performance.
Han et al. [408] prepared hollow carbon hemispheres (HCHs) with nitrogen
content of 10.9 wt% by template method: (1) using silicon spheres with diameter
of about 300 nm as template, 3-MBP-dca (3-metal-1-butylpyridine Dicya nide), or
CMIM-Cl (3 - (3-cyanopropyl) - 1-methyl-1 h-imida-zol-3-iumchloride) is coated on
the silicon ball; (2) the coated silicon ball is carbonized; (3) the template is removed
with NH 4 HF 2 ; (4) the high-temperature (900 °C) annealing treatment is carried out
to form the structure of porous hemisphere, as shown in Fig. 4.48a-d. The ORR
performance of the obtained nitrogen-doped HCHs is close to that of Pt/C catalyst,
as shown in Fig. 4.48e.
BO et al. [409] prepared ordered mesoporous boron-doped carbons (BOMCs)
using SBA-15 as template, 4- hydroxyphenylboronic acid as carbon source and
boron source. The specific surface area of BOMCs can reach 900 m
2 g
−1 , the average
pore diameter is 6.4 nm, and the nitrogen content is 1.3%. The ORR performance
test results in 0.1 M KOH solution show that its peak potential reaches 0.16 (VS.
Ag/AgCl), and the electron transfer number obtained by K-L equation is 3.86, indicating that the ORR process of BOMCs is mainly a direct four-electron process.
There are many forms of B doping into C structure, including BC 3 , BC 4 , BC 2 O,
BCO 2 , etc. Among them, BC 3 and BC 4 are considered to play a key role in ORR
process, and their content also directly affects the performance of ORR. The higher
the content, the greater the ORR activity [410].
The P atom has the same valence electrons and similar chemical properties as
N, but because the larger atomic radius and stronger electronegativity of the P atom
are weaker than that of C, the combination of P and C will make C have positive
charge, thus promoting ORR like N-doping. Yang et al. [411] prepared P-doped
ordered mesoporous carbon (POMC) using SBA-15 as a template and a method
of co-splitting P source and C source under the condition of not using any metal:
firstly, using P-containing carbon source triphenylphosphine, (TPP) and initial carbon
source (phenol) are immersed in template SBA-15 at room temperature, then cracked
at 900 °C under argon atmosphere, and finally the template is removed by HF treatment, as shown in Fig. 4.49a. Under the same conditions, the ORR performance of
POMC is very close to Pt/C, as shown in Fig. 4.49e. Their research shows that the
ORR activity of POMC with different lengths prepared from templates of different
sizes will be different. The shorter the length, the better the ORR activity, because
the shorter the length, the smaller the charge transfer resistance.
Wu et al. [412] first use resorcinol and formaldehyde as c sources and Co(NO 3 ) 2
as catalyst precursors, first prepare Co–C precursors by sol–gel method, then add
H 3 PO 4 (P source), heat treat at 800 oC for 1 h, and then treat with 1 M HCl solution
161
nitrogen content has higher oxygen reduction activity. Yang et al. [407] prepared
porous nitrogen-doped carbon with high surface area using silicon nanoparticles
as template. The specific surface area of the material reached 1500 m
2 g
−1 , and it
had narrow mesoporous distribution (12 nm), and its oxygen reduction performance
was discussed. They found that the oxygen reduction activity of these materials was
close to that of commercial Pt/C catalyst, and that the porous nitrogen-doped carbon
with high specific surface area obtained by carbonizing base materials had better
performance.
Han et al. [408] prepared hollow carbon hemispheres (HCHs) with nitrogen
content of 10.9 wt% by template method: (1) using silicon spheres with diameter
of about 300 nm as template, 3-MBP-dca (3-metal-1-butylpyridine Dicya nide), or
CMIM-Cl (3 - (3-cyanopropyl) - 1-methyl-1 h-imida-zol-3-iumchloride) is coated on
the silicon ball; (2) the coated silicon ball is carbonized; (3) the template is removed
with NH 4 HF 2 ; (4) the high-temperature (900 °C) annealing treatment is carried out
to form the structure of porous hemisphere, as shown in Fig. 4.48a-d. The ORR
performance of the obtained nitrogen-doped HCHs is close to that of Pt/C catalyst,
as shown in Fig. 4.48e.
BO et al. [409] prepared ordered mesoporous boron-doped carbons (BOMCs)
using SBA-15 as template, 4- hydroxyphenylboronic acid as carbon source and
boron source. The specific surface area of BOMCs can reach 900 m
2 g
−1 , the average
pore diameter is 6.4 nm, and the nitrogen content is 1.3%. The ORR performance
test results in 0.1 M KOH solution show that its peak potential reaches 0.16 (VS.
Ag/AgCl), and the electron transfer number obtained by K-L equation is 3.86, indicating that the ORR process of BOMCs is mainly a direct four-electron process.
There are many forms of B doping into C structure, including BC 3 , BC 4 , BC 2 O,
BCO 2 , etc. Among them, BC 3 and BC 4 are considered to play a key role in ORR
process, and their content also directly affects the performance of ORR. The higher
the content, the greater the ORR activity [410].
The P atom has the same valence electrons and similar chemical properties as
N, but because the larger atomic radius and stronger electronegativity of the P atom
are weaker than that of C, the combination of P and C will make C have positive
charge, thus promoting ORR like N-doping. Yang et al. [411] prepared P-doped
ordered mesoporous carbon (POMC) using SBA-15 as a template and a method
of co-splitting P source and C source under the condition of not using any metal:
firstly, using P-containing carbon source triphenylphosphine, (TPP) and initial carbon
source (phenol) are immersed in template SBA-15 at room temperature, then cracked
at 900 °C under argon atmosphere, and finally the template is removed by HF treatment, as shown in Fig. 4.49a. Under the same conditions, the ORR performance of
POMC is very close to Pt/C, as shown in Fig. 4.49e. Their research shows that the
ORR activity of POMC with different lengths prepared from templates of different
sizes will be different. The shorter the length, the better the ORR activity, because
the shorter the length, the smaller the charge transfer resistance.
Wu et al. [412] first use resorcinol and formaldehyde as c sources and Co(NO 3 ) 2
as catalyst precursors, first prepare Co–C precursors by sol–gel method, then add
H 3 PO 4 (P source), heat treat at 800 oC for 1 h, and then treat with 1 M HCl solution