4 Catalyst Materials for Oxygen Reduction Reaction
159
Zheng et al. [402] prepared B, N-graphene by two-step method. Firstly, GO was
annealed at a lower temperature (500 °C) in an NH 3 atmosphere to form N-graphene,
and then the mixture of N-graphene and H3BO 3 was heat-treated at a high temperature (900 °C) to form B, N-graphene. B atom is further doped into N-graphene to
form B, N-graphene. The N content of B, N-graphene is 4.22% and the B content is
2.17%, in which the bond form of B is only B-C bond. Compared with the preparation
of single impurity atom doped N-graphene and B-graphene, the ORR performance
of B, N-graphene in 0.1 M kOH is significantly improved.
Density functional theory calculation shows that the synergistic effect caused
by the chemical coupling between B and N is the reason for the enhanced ORR
performance of B, N-graphene. In the benzene ring structure of B-C-N, 2p orbit,
and N of C atom located between N and B atoms produce polarization, providing
additional electrons to B atom nearby; 2p orbit of B atom is occupied by electrons, the
synergistic coupling effect of charge transfer can effectively improve the adsorption
and binding of HO 2 , thus promoting the occurrence of ORR. In this synergistic
effect, the functions of N and B with different doping forms are different. Unlike in
N-graphene, graphite nitrogen promotes the adsorption of HO 2 on the neighboring C
atom, in B, N-graphene, only pyridine nitrogen can promote the adsorption of HO 2
on the active B site [402].
Wang et al. [375] prepared a series of B/N Co-doped graphene (BCN) with
adjustable content by heat treating the mixture of go and boric acid in the atmosphere of NH 3 . The ORR activity of BCN was higher than that of Pt/C catalyst.
Wang et al. [404] prepared N and S Co-doped graphene (NSG) by one-step method:
using go and thiourea as precursors, NSG was obtained by heat treatment in argon
atmosphere, in which thiourea was used as both N source and S source, and the N
content decreased with the increase of heat treatment temperature, while the S content
increased with the increase of heat treatment temperature. In addition, thiourea also
partially reduced go during heat treatment. NSG showed good ORR activity in 0.1 M
kOH medium: high peak potential, high current density, and high stability. See Table
4.4 for ORR activity comparison of doped graphene non-metallic catalyst.
4.6.7 Other Doped Carbon Materials
The special structure of carbon material makes it rich in diversity. Carbon nanotubes
and graphene are two kinds of very special nanocarbon materials. Since Dai et al.
[334] found that VA -NCNTs as a non-metallic catalyst showed excellent ORR
activity, other forms of doped carbon nanomaterials have attracted a lot of attention
and research. Klaus et al. [406] have studied ordered nitrogen-doped mesoporous
graphite arrays with moderate nitrogen content (Nitrogen-Doped Ordered Mesoporous Graphitic Arrays, NOMGAs), The oxygen reduction activity, stability, and
anti-toxic ability of nomgas in 0.1 M kOH are higher than that of Pt/C catalyst. In
their research, they found that graphite-like nitrogen atoms play an important role in
the process of oxygen reduction, and pointed out that the catalyst with high graphite
159
Zheng et al. [402] prepared B, N-graphene by two-step method. Firstly, GO was
annealed at a lower temperature (500 °C) in an NH 3 atmosphere to form N-graphene,
and then the mixture of N-graphene and H3BO 3 was heat-treated at a high temperature (900 °C) to form B, N-graphene. B atom is further doped into N-graphene to
form B, N-graphene. The N content of B, N-graphene is 4.22% and the B content is
2.17%, in which the bond form of B is only B-C bond. Compared with the preparation
of single impurity atom doped N-graphene and B-graphene, the ORR performance
of B, N-graphene in 0.1 M kOH is significantly improved.
Density functional theory calculation shows that the synergistic effect caused
by the chemical coupling between B and N is the reason for the enhanced ORR
performance of B, N-graphene. In the benzene ring structure of B-C-N, 2p orbit,
and N of C atom located between N and B atoms produce polarization, providing
additional electrons to B atom nearby; 2p orbit of B atom is occupied by electrons, the
synergistic coupling effect of charge transfer can effectively improve the adsorption
and binding of HO 2 , thus promoting the occurrence of ORR. In this synergistic
effect, the functions of N and B with different doping forms are different. Unlike in
N-graphene, graphite nitrogen promotes the adsorption of HO 2 on the neighboring C
atom, in B, N-graphene, only pyridine nitrogen can promote the adsorption of HO 2
on the active B site [402].
Wang et al. [375] prepared a series of B/N Co-doped graphene (BCN) with
adjustable content by heat treating the mixture of go and boric acid in the atmosphere of NH 3 . The ORR activity of BCN was higher than that of Pt/C catalyst.
Wang et al. [404] prepared N and S Co-doped graphene (NSG) by one-step method:
using go and thiourea as precursors, NSG was obtained by heat treatment in argon
atmosphere, in which thiourea was used as both N source and S source, and the N
content decreased with the increase of heat treatment temperature, while the S content
increased with the increase of heat treatment temperature. In addition, thiourea also
partially reduced go during heat treatment. NSG showed good ORR activity in 0.1 M
kOH medium: high peak potential, high current density, and high stability. See Table
4.4 for ORR activity comparison of doped graphene non-metallic catalyst.
4.6.7 Other Doped Carbon Materials
The special structure of carbon material makes it rich in diversity. Carbon nanotubes
and graphene are two kinds of very special nanocarbon materials. Since Dai et al.
[334] found that VA -NCNTs as a non-metallic catalyst showed excellent ORR
activity, other forms of doped carbon nanomaterials have attracted a lot of attention
and research. Klaus et al. [406] have studied ordered nitrogen-doped mesoporous
graphite arrays with moderate nitrogen content (Nitrogen-Doped Ordered Mesoporous Graphitic Arrays, NOMGAs), The oxygen reduction activity, stability, and
anti-toxic ability of nomgas in 0.1 M kOH are higher than that of Pt/C catalyst. In
their research, they found that graphite-like nitrogen atoms play an important role in
the process of oxygen reduction, and pointed out that the catalyst with high graphite