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Y. Li et al.
carbon source on a porous metal or nanoparticle surface by chemical vapor deposition (CVD) or heat treatment to form a three-dimensional structured graphene. It is
mainly synthesized by stereo porous metal catalysis or metal nanoparticle catalysis.
Recent studies have shown that three-dimensional graphene is also an excellent
catalyst material for oxygen reduction. Compared with two-dimensional graphene,
three-dimensional graphene not only maintains the intrinsic characteristics of
graphene, but also has unique self-supporting structure and porosity, which can
provide good three-dimensional electron transmission path and rapid mass transfer.
In addition, the three-dimensional graphene can also provide large specific surface
area, high mechanical strength, uniform dispersion of a large number of catalyst
nanoparticles, and high electrochemical stability [83, 84].
Three-dimensional graphene as a catalyst carrier for platinum loading has first
attracted attention [84]. Wang et al. [84] prepared Pt/3D graphene catalyst by
depositing platinum catalyst on the surface of three-dimensional graphene synthesized by CVD method. Compared with the carbon fiber carrier, the platinum catalyst
supported by the carrier has higher catalytic performance and service life. In addition,
non-noble metals supported by graphene with three-dimensional structure have also
attracted attention. Wu et al. [1] prepared a Fe 3 O 4 /N-GAs non-noble metal catalyst
by uniformly depositing Fe 3 O 4 on the surface of nitrogen-doped cubic graphene gel
(N-GAS). The preparation process is shown in Fig. 4.4. Firstly, GO solution, iron
acetate, and polypyrrole are ultrasonically dispersed to form a uniform and stable
suspension, and then the suspension is put into a hydrothermal reaction autoclave
and heated for 12 h at 180 °C to obtain a three-dimensional gel-like compound,
and then the solid gel-like compound is freeze-dried, and heat-treated for 3 h at
600 °C under nitrogen to finally obtain the sample. The preparation process promotes
Fe 3 O 4 nanoparticles to be deposited on the surface of graphene and is accompanied
by a nitrogen-doping process. Compared with the catalyst in which nanoparticles
are deposited on nitrogen-doped two-dimensional graphene and carbon black, the
Fe 3 O 4 /N-GAs catalyst has a more positive peaking potential and a higher current
density for oxygen reduction tests under alkaline conditions. This further proves
that the three-dimensional graphene can improve the electrocatalytic performance
of the oxygen reduction catalyst. In addition, the three-dimensional graphene is not
only used as a catalyst carrier to support platinum and non-noble metal catalysts,
but also used as a non-metal catalyst itself. For example, doped graphene with N,
P, S, B mono-, binary, or multi-component structure, which is used as an oxygen
reduction catalyst, exhibits catalytic activity close to or even better than commercial
Pt/C under acidic or alkaline conditions, while its stability and lifetime are far better
than commercial Pt/C [85–89].
Professor Shen Peikang’s research group of Guangxi University proposed a new
polymer pyrolysis method to prepare self-doped three-dimensional porous graphene
(3D HPG) with adjustable porosity and specific surface area [45]. The preparation
process is shown in Fig. 4.5. Firstly, the pretreated polymer is exchanged with metal
ions (such as Ni
2+ ), then the dried polymer exchanged with metal ions is added into
KOH/ethanol solution, evenly stirred, heated, and evaporated to dryness until a pasty
mixed solution is formed, then the pasty mixed solution is dried and pulverized at
Y. Li et al.
carbon source on a porous metal or nanoparticle surface by chemical vapor deposition (CVD) or heat treatment to form a three-dimensional structured graphene. It is
mainly synthesized by stereo porous metal catalysis or metal nanoparticle catalysis.
Recent studies have shown that three-dimensional graphene is also an excellent
catalyst material for oxygen reduction. Compared with two-dimensional graphene,
three-dimensional graphene not only maintains the intrinsic characteristics of
graphene, but also has unique self-supporting structure and porosity, which can
provide good three-dimensional electron transmission path and rapid mass transfer.
In addition, the three-dimensional graphene can also provide large specific surface
area, high mechanical strength, uniform dispersion of a large number of catalyst
nanoparticles, and high electrochemical stability [83, 84].
Three-dimensional graphene as a catalyst carrier for platinum loading has first
attracted attention [84]. Wang et al. [84] prepared Pt/3D graphene catalyst by
depositing platinum catalyst on the surface of three-dimensional graphene synthesized by CVD method. Compared with the carbon fiber carrier, the platinum catalyst
supported by the carrier has higher catalytic performance and service life. In addition,
non-noble metals supported by graphene with three-dimensional structure have also
attracted attention. Wu et al. [1] prepared a Fe 3 O 4 /N-GAs non-noble metal catalyst
by uniformly depositing Fe 3 O 4 on the surface of nitrogen-doped cubic graphene gel
(N-GAS). The preparation process is shown in Fig. 4.4. Firstly, GO solution, iron
acetate, and polypyrrole are ultrasonically dispersed to form a uniform and stable
suspension, and then the suspension is put into a hydrothermal reaction autoclave
and heated for 12 h at 180 °C to obtain a three-dimensional gel-like compound,
and then the solid gel-like compound is freeze-dried, and heat-treated for 3 h at
600 °C under nitrogen to finally obtain the sample. The preparation process promotes
Fe 3 O 4 nanoparticles to be deposited on the surface of graphene and is accompanied
by a nitrogen-doping process. Compared with the catalyst in which nanoparticles
are deposited on nitrogen-doped two-dimensional graphene and carbon black, the
Fe 3 O 4 /N-GAs catalyst has a more positive peaking potential and a higher current
density for oxygen reduction tests under alkaline conditions. This further proves
that the three-dimensional graphene can improve the electrocatalytic performance
of the oxygen reduction catalyst. In addition, the three-dimensional graphene is not
only used as a catalyst carrier to support platinum and non-noble metal catalysts,
but also used as a non-metal catalyst itself. For example, doped graphene with N,
P, S, B mono-, binary, or multi-component structure, which is used as an oxygen
reduction catalyst, exhibits catalytic activity close to or even better than commercial
Pt/C under acidic or alkaline conditions, while its stability and lifetime are far better
than commercial Pt/C [85–89].
Professor Shen Peikang’s research group of Guangxi University proposed a new
polymer pyrolysis method to prepare self-doped three-dimensional porous graphene
(3D HPG) with adjustable porosity and specific surface area [45]. The preparation
process is shown in Fig. 4.5. Firstly, the pretreated polymer is exchanged with metal
ions (such as Ni
2+ ), then the dried polymer exchanged with metal ions is added into
KOH/ethanol solution, evenly stirred, heated, and evaporated to dryness until a pasty
mixed solution is formed, then the pasty mixed solution is dried and pulverized at