Page 144 - Read Online

Chen et al. Microstructures 2023;3:2023025 https://dx.doi.org/10.20517/microstructures.2023.12 Page 13 of 31

of Pt/CeO /N-C only negatively shifted by 5 mV after a durability test for 10,000 cycles, while it is 43 mV for
2
Pt/C (as shown in Figure 6E). The enhanced ORR activity and durability of Pt/CeO /N-C can be attributed
2
to the abundance of oxygen vacancies present on the CeO surface, leading to a strong interaction between
2
the Pt-CeO interface.
2
Tungsten oxides (WO )
3
Tungsten oxide is another metal oxide with superior inherent properties and durability in acidic media.
Tungsten trioxide (WO ), as the most stable oxidation state, has been proposed as a promising support for
3
Pt-based electrocatalysts in the ORR due to its series of advantages, which include: (1) the W possesses
strong electronegativity, which can modify the electronic structure of Pt and tune the Pt-Pt distance, thereby
facilitating the ORR kinetic; (2) WO can introduce hydrogen spillover effect on Pt via the formation of
3
hydrogen tungsten bronze (H WO ), which speeds up the protonation of the O molecule and the rate of
2
x
3
oxygen reduction on Pt NPs; (3) the unusual structural defects and unique surface features of WO can
3
promote the high dispersion of the Pt NPs and narrow size distribution; (4) the synergistic effect and SMSI
effect between Pt and WO enable Pt/WO catalyst to achieve higher ORR activity and stability. Kim et al.
3
3
synthesized a Pt/black WO nanofiber (NF) catalyst with controlled oxygen deficiency and high electrical
3-x
conductivity (as shown in Figure 6F) . Their investigations revealed that the as-prepared Pt/black WO
[100]
3-x
NFs exhibited better ORR activity and durability in acidic media as compared to Pt/white WO NFs and
3-x
Pt/C catalysts. Combined with DFT calculations suggested that the high ORR performance was attributed to
plentiful ORR active sites facilitated by numerous oxygen vacancies on the black WO surface and the
3-x
excellent surface charge properties of the Pt NPs, and the enhanced stability is attributed to the SMSI effect
between Pt and oxygen-deficient WO (as shown in Figure 6G). In addition, Pt/WO -C system catalysts
3-x
3
have been reported to have high ORR activity and stability because of the combination of the excellent
electrical conductivity of carbon nanomaterials and the strong interaction at the Pt-W interface [101,102] .
Interestingly, besides as a support for Pt NPs or a modified part of the carbon substrate, the WO has also
3
been applied to modify the catalyst surface. For example, Mo et al. prepared a WO -surface modified PtNi
x
alloy nanowires (WO -PtNi NWs) catalyst with a high aspect ratio by a one-step solvothermal method,
x
-1
which showed a superior mass activity of 0.85 A mg at 0.9V than PtNi NWs (0.33 A mg ) and Pt/C
-1
pt
pt
-1 [103]
(0.14 A mg ) . Meanwhile, the mass activity of WO -PtNi NWs only dropped 23.89% after the 30 k
pt
x
cycles durability test, whereas it is 45.94% and 57.9% for PtNi NWs and Pt/C, respectively .
[104]
Besides TiO , CeO , and WO , other reducible oxide supports, such as NbO and Ta O 5 [105,106] , have also
[67]
2
2
2
2
3
been demonstrated to be capable of enhancing the ORR performance through the SMSI effect with Pt NPs.
Some newly published literature for Pt/TMO catalysts with the performance of ORR is given in Table 2.
However, in a three-electrode system, a high-speed rotating disc electrode can eliminate the influence of
mass transfer and conductivity on the performance of oxide-supported Pt-based catalysts due to the limited
conductivity and low specific surface area of oxide supports, however, in practical applications, thicker
catalyst layers will require higher mass transfer and conduction capabilities of the catalyst. As a result, there
are few reports of Pt-based catalysts supported by oxide carriers for hydrogen fuel cells or metal-air
batteries.
Nitrides-based materials
TMNs, especially titanium nitride (TiN), niobium nitride (NbN), etc., are used as electrocatalysts because of
their excellent electronic conductivity, electrochemical and thermal stability, and corrosion resistance
compared with TMOs. In addition, TMNs inherit the characteristics of TMOs in terms of wide source and
low price since their synthesis is mainly using TMOs as precursors and roasted under ammonia
atmosphere. The excellent corrosion resistance and SMSI facilitate the high catalytic stability and a
prolonged lifetime of TMNs-supported catalysts. More importantly, the high electronic conductivity of