4 Catalyst Materials for Oxygen Reduction Reaction
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the nanoparticles loaded on its surface have large size and poor dispersibility, thus
greatly reducing the catalytic activity of the electrocatalyst [1]. In order to uniformly
support metal catalyst nanoparticles on CNTs surface, there are usually two treatment
methods, one is covalent method, i.e., chemical oxidation of CNTs surface with some
strong acid or strong oxidant. This method will reduce the conductivity and stability
of CNTs. Another non-covalent method is to modify its surface with some surfactants or polymers to form a large number of uniform surface groups on its surface,
so that the metal catalyst nanoparticles can be loaded on it in a large number and
uniformly. The advantage of this method is that the original physical and chemical
properties of CNTs can be maintained, but the stability and electrochemical activity
of the prepared catalyst are directly affected by the surfactant or polymer structure.
Zhang et al. [18] modified positively charged poly (allylamine hydrochloride, PAH)
on the surface of CNTs, then adsorbed negatively charged PtCl 6
2− on the surface of
CNTs through electrostatic action, and then PtCl 6
2− was then reduced in situ with
ethylene glycol, so that Pt nanoparticles were uniformly loaded on the surface of
CNTs, thus obtaining Pt/PAH-CNTs catalyst, which showed high electrochemical
activity area. More importantly, in 0.5 mol·L
−1 H 2 SO 4 solution, the catalytic activity
of Pt/PAH-CNTs catalyst for oxygen reduction is 1.85 times that of Pt/COOH-CNTs
(acid-treated CNTs), which is mainly due to the high Pt electrocatalytic activity area
and good conductivity of Pt/PAH-CNTs catalyst. Pt nanoparticles were deposited on
the surface of graphitized CNT by a similar non-covalent method, and the prepared
electrocatalyst showed high oxygen reduction electrocatalytic activity and stability.
4.1.1.3 Mesoporous Carbon
Mesoporous carbon (MPC) is a kind of porous carbon material which pore diameter
is mainly distributed in 2–50 nm. According to its internal structure and preparation
method, it can be divided into two types [19]: one is ordered mesoporous carbon
(OMC) and the other is disordered mesoporous carbon (DOMC). Although DOMC
is rich in mesopores, the mesopores it contains are disordered and connected irregularly, so compared with OMC, DOMC has relatively poor conductivity and relatively
wide pore size distribution. OMC, as a catalyst carrier material, is more conducive
to improving the catalytic activity of the catalyst because of its large specific surface
area, high conductivity, and easy mass transfer. MPC has been widely studied as a
carrier material for oxygen reduction catalysts. Compared with traditional carbon
materials, MPC has more advantages as a carrier material for oxygen reduction
catalysts because of its single three-dimensional interconnected mesopores. In addition, Pt [20, 21] or Pt alloy [22, 23] supported by MPC all exhibit good electrocatalytic performance for oxygen reduction, which is mainly attributed to the good
dispersibility of metal catalyst, the high conductivity of MPC, and its characteristic
of special pore structure and easy mass transfer [24]. As is known to all, a highperformance oxygen reduction electrocatalyst needs an effective reaction region on
a nanometer scale, such as a three-phase interface. In this region, when the electrochemical reaction is carried out, it is easy to transport materials (reactants and
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the nanoparticles loaded on its surface have large size and poor dispersibility, thus
greatly reducing the catalytic activity of the electrocatalyst [1]. In order to uniformly
support metal catalyst nanoparticles on CNTs surface, there are usually two treatment
methods, one is covalent method, i.e., chemical oxidation of CNTs surface with some
strong acid or strong oxidant. This method will reduce the conductivity and stability
of CNTs. Another non-covalent method is to modify its surface with some surfactants or polymers to form a large number of uniform surface groups on its surface,
so that the metal catalyst nanoparticles can be loaded on it in a large number and
uniformly. The advantage of this method is that the original physical and chemical
properties of CNTs can be maintained, but the stability and electrochemical activity
of the prepared catalyst are directly affected by the surfactant or polymer structure.
Zhang et al. [18] modified positively charged poly (allylamine hydrochloride, PAH)
on the surface of CNTs, then adsorbed negatively charged PtCl 6
2− on the surface of
CNTs through electrostatic action, and then PtCl 6
2− was then reduced in situ with
ethylene glycol, so that Pt nanoparticles were uniformly loaded on the surface of
CNTs, thus obtaining Pt/PAH-CNTs catalyst, which showed high electrochemical
activity area. More importantly, in 0.5 mol·L
−1 H 2 SO 4 solution, the catalytic activity
of Pt/PAH-CNTs catalyst for oxygen reduction is 1.85 times that of Pt/COOH-CNTs
(acid-treated CNTs), which is mainly due to the high Pt electrocatalytic activity area
and good conductivity of Pt/PAH-CNTs catalyst. Pt nanoparticles were deposited on
the surface of graphitized CNT by a similar non-covalent method, and the prepared
electrocatalyst showed high oxygen reduction electrocatalytic activity and stability.
4.1.1.3 Mesoporous Carbon
Mesoporous carbon (MPC) is a kind of porous carbon material which pore diameter
is mainly distributed in 2–50 nm. According to its internal structure and preparation
method, it can be divided into two types [19]: one is ordered mesoporous carbon
(OMC) and the other is disordered mesoporous carbon (DOMC). Although DOMC
is rich in mesopores, the mesopores it contains are disordered and connected irregularly, so compared with OMC, DOMC has relatively poor conductivity and relatively
wide pore size distribution. OMC, as a catalyst carrier material, is more conducive
to improving the catalytic activity of the catalyst because of its large specific surface
area, high conductivity, and easy mass transfer. MPC has been widely studied as a
carrier material for oxygen reduction catalysts. Compared with traditional carbon
materials, MPC has more advantages as a carrier material for oxygen reduction
catalysts because of its single three-dimensional interconnected mesopores. In addition, Pt [20, 21] or Pt alloy [22, 23] supported by MPC all exhibit good electrocatalytic performance for oxygen reduction, which is mainly attributed to the good
dispersibility of metal catalyst, the high conductivity of MPC, and its characteristic
of special pore structure and easy mass transfer [24]. As is known to all, a highperformance oxygen reduction electrocatalyst needs an effective reaction region on
a nanometer scale, such as a three-phase interface. In this region, when the electrochemical reaction is carried out, it is easy to transport materials (reactants and