98
Y. Li et al.
Pt/C performance. Its superior performance is mainly due to the fact that Pt is evenly
distributed on the tungsten carbide surface of the carbon support, which results in
the formation of more electrochemically active areas. In addition, tungsten carbide
has a synergistic effect not only with platinum, but also with other metal catalysts
(such as Au, Pd, etc.). For example, Shen et al. [108] prepared AuPd-WC/C catalysts
by depositing AuPd alloys onto WC by alternating microwave method. This electrocatalyst exhibits much better electrocatalytic performance for oxygen reduction
than commercial Pt/C catalysts. In addition, tungsten carbide also shows good longterm stable performance [111, 112]. Tungsten carbides mainly exist in two forms of
WC and W 2 C, while W 2 C is thermodynamically unstable at room temperature, but
WC thermodynamics is very stable [113]. In order to confirm that WC also has good
stability under electrocatalytic conditions, Zellner et al. [114] tested the prepared WC
film in 0.5 mol·L
–1 H 2 SO 4 medium. The results confirm that the WC film exhibits a
stable electrochemical performance at a potential below 0.6 V. There is an unstable
region for W 2 C, which is mainly caused by the oxidation of W 2 C in the air during the
electrocatalytic process to produce the intermediate product W x O y [2]. Chhina et al.
[115] used a multi-potential step method (constant 20 s at 1.8 V and 60 s at 0.6 V
for one cycle) to perform accelerated aging tests on Pt/WC and WC. After 30 cycles,
Stability is only reduced by 20 and 10%, respectively; however, commercial Pt/C
decays completely after only 10 turns. For the WC stability test, a small amount of
WO x will be generated, which is a short-bandwidth semiconductor material and has
a certain electron conductivity. Therefore, when the WC is oxidized, the structure of
the carrier is partially changed, and the Pt load on the WC surface becomes Pt load
on the WO x -coated WC surface [115]. This mechanism is not like a carbon support,
which will be oxidized to CO or CO 2 , which will cause Pt to fall off and agglomerate
from the surface of the support, which will greatly reduce the effective utilization
area of Pt, which will cause the oxygen reduction performance of the catalyst to
decrease sharply [111]. Although carbides have so many advantages, for carbides, as
catalyst supports, further improvements are needed [115]. For example, the specific
surface area of WC is very low, so it is necessary to further increase the effective
utilization area of Pt by reducing the size of Pt nanoparticles (e.g., the size of Pt
nanoparticles is optimized from 30 to 3 nm) to achieve higher mass activity [115].
4.1.2.3 Nitride
Nitrides, especially transition metal nitrides, have been widely used in coatings, such
as cutting tools and refractory materials, due to their unique physical and chemical
properties, such as strong hardness and good wear resistance. Because transition
metal nitrides have an electronic structure similar to that of precious metals [116],
they are considered as alternatives in various heterogeneous catalysis such as isomerization reactions [117], hydrodesulfurization reactions, hydrogenation reactions, etc.
Best candidate for platinum catalyst [116]. Recently, as nitrides are considered to
have better electrical conductivity, thermal and electrochemical stability, corrosion
resistance, and good synergistic effects, they have also been widely used as oxygen
Y. Li et al.
Pt/C performance. Its superior performance is mainly due to the fact that Pt is evenly
distributed on the tungsten carbide surface of the carbon support, which results in
the formation of more electrochemically active areas. In addition, tungsten carbide
has a synergistic effect not only with platinum, but also with other metal catalysts
(such as Au, Pd, etc.). For example, Shen et al. [108] prepared AuPd-WC/C catalysts
by depositing AuPd alloys onto WC by alternating microwave method. This electrocatalyst exhibits much better electrocatalytic performance for oxygen reduction
than commercial Pt/C catalysts. In addition, tungsten carbide also shows good longterm stable performance [111, 112]. Tungsten carbides mainly exist in two forms of
WC and W 2 C, while W 2 C is thermodynamically unstable at room temperature, but
WC thermodynamics is very stable [113]. In order to confirm that WC also has good
stability under electrocatalytic conditions, Zellner et al. [114] tested the prepared WC
film in 0.5 mol·L
–1 H 2 SO 4 medium. The results confirm that the WC film exhibits a
stable electrochemical performance at a potential below 0.6 V. There is an unstable
region for W 2 C, which is mainly caused by the oxidation of W 2 C in the air during the
electrocatalytic process to produce the intermediate product W x O y [2]. Chhina et al.
[115] used a multi-potential step method (constant 20 s at 1.8 V and 60 s at 0.6 V
for one cycle) to perform accelerated aging tests on Pt/WC and WC. After 30 cycles,
Stability is only reduced by 20 and 10%, respectively; however, commercial Pt/C
decays completely after only 10 turns. For the WC stability test, a small amount of
WO x will be generated, which is a short-bandwidth semiconductor material and has
a certain electron conductivity. Therefore, when the WC is oxidized, the structure of
the carrier is partially changed, and the Pt load on the WC surface becomes Pt load
on the WO x -coated WC surface [115]. This mechanism is not like a carbon support,
which will be oxidized to CO or CO 2 , which will cause Pt to fall off and agglomerate
from the surface of the support, which will greatly reduce the effective utilization
area of Pt, which will cause the oxygen reduction performance of the catalyst to
decrease sharply [111]. Although carbides have so many advantages, for carbides, as
catalyst supports, further improvements are needed [115]. For example, the specific
surface area of WC is very low, so it is necessary to further increase the effective
utilization area of Pt by reducing the size of Pt nanoparticles (e.g., the size of Pt
nanoparticles is optimized from 30 to 3 nm) to achieve higher mass activity [115].
4.1.2.3 Nitride
Nitrides, especially transition metal nitrides, have been widely used in coatings, such
as cutting tools and refractory materials, due to their unique physical and chemical
properties, such as strong hardness and good wear resistance. Because transition
metal nitrides have an electronic structure similar to that of precious metals [116],
they are considered as alternatives in various heterogeneous catalysis such as isomerization reactions [117], hydrodesulfurization reactions, hydrogenation reactions, etc.
Best candidate for platinum catalyst [116]. Recently, as nitrides are considered to
have better electrical conductivity, thermal and electrochemical stability, corrosion
resistance, and good synergistic effects, they have also been widely used as oxygen